october 2014 - power systems design · extending battery life in wireless medical devices (pg 12 )...

October 2014

Special Report: Health Medical & Mobility (pg 33)

VIEWpoint

Let’s change the keyboard!By Alix Paultre, Editorial Director, Power Systems Design

POWERline

Keithley’s Model 2657A-PM-200 protection module

POWERplayer

Investing in tomorrow’s engineersBy Phil Scotcher, TDK-Lamba

MARKETwatch

Medical market driven by emerging regionsBy Jonathan Eykyn, IHS Technology

DESIGNtips

Source interaction with board-mount converters

By Dr. Ray Ridley, Ridley Engineering

COVER STORY

Extending battery life in wireless

medical devices

By Jehangir Parvereshi, SiTime

TECHNICAL FEATURES

Battery Charging & Management

Get a constant output switching with a +5v input and a single-cell batteryBy Don Corey, Maxim Integrated

Serving the Grid

Automating ecological energy generationBy Scott Ludwig, Progea

Power Semiconductors

A 4.5kV IGBT/Diode Chip set for HVDC transmission appsBy Thomas Schütze, Infineon Technologies

Power Supplies

Smart PFC and DC/DC converter system offers optimum efficiencyBy Dr. Bernhard Strzalkowski,

Analog Devices

SPECIAL REPORT:HEALTH MEDICAL & MOBILITY

Dell Children’s Medical Center

saves power with LED lighting

By Karyn Gayle, Acuity Brands

Proper ESD protection is key to

ensuring reliability of medical

wearables

By James Colby, Littelfuse

Compact regulator speeds digital

endoscopy adoption

By Afshin Odabaee, Linear Technology

2

PODCASThighlights

PSD multimedia highlightsBy Alix Paultre, Editorial Director, Power Systems Design

GREENpage

The new luddites By Alix Paultre, Editorial Director, Power Systems Design

Dilbert

48

44

7

6

37

4

Highlighted Products News, Industry News and

more web-only content, to:

www.powersystemsdesign.com

POWER SYSTEMS DESIGN 2014OCTOBER

1WWW.POWERSYSTEMSDESIGN.COM

40

13

13

8

48

COVER STORY

Extending battery life in wireless medical devices (pg 12 )

34

12

18

20

25

29

300 Watts.Zero Wait.

We’ve packed a lot of performance into our new compact planar transformers. Rated for 300 Watts, the PL300 Series offers DCR as low as 7.2 mOhms and leakage induc-tance down to 0.25 µH.

They are AEC-Q200 Grade 1 qualified for automotive applications and provide 1500 Vrms primary-to-secondary isolation.

Coilcraft PL300 Series planar transformers. Stacked with performance. Available from stock.

WWW.COILCRAFT.COM

Best of all, these Coilcraft planars are available from stock, so order your free evaluation samples today!

Learn more about the PL300 and its 160 Watt companion, the PL160, by visiting us online at www.coilcraft.com/PL.

Coilcraft also offers the 160 W rated PL160 Series

®

4

VIEWpoint

WWW.POWERSYSTEMSDESIGN.COM

POWER SYSTEMS DESIGN

As we hurtle into the future, literally making it up as we go along, it is sometimes useful to re-examine some of the primary tools we use to see if modern technology can enhance them, modified their original purpose, or has superseded them. In this case we’ll look at the keyboard, one of our primary interfaces between ourselves as well as our technology.

The first printersThe typewriter was the first (semi)portable printing device, and it contin-ued the acceleration of change first set into motion by Gutenberg centuries ago. The shift in ability from being able to create typeset (“type” being the individual sculpted letter first created by Gurenberg, and “set” meaning to place it into frames as blocks of text) documents, greatly enhancing both the speed, reproducibility, clarity, and uniformity (a singular font is easier to read) of correspondence.

As technology progressed, the typewriter helped spawn the computer while still retaining its utility as a portable printing device. It is only now that we are entering a true paperless age that it has fallen out of favor. Unfortu-nately the dead hand of technology inertia keeps us shackled to the

There is a Wikipedia debate going on about the true origin of the QWERTY keyboard, but it doesn’t matter where it came from if it isn’t appropriate for the way we use keyboards now. There are two aspects to keyboard modern-ization: the letters, and the other keys.

Keyboard letter orderAs mentioned, it doesn’t really matter where the QWERTY keyboard came from, the issue is should we retain it? The number of people who can touch-type is a sadly shrinking number (myself included), and are our feelings important enough to hold back the future? How about the Dvorak keyboard, at least there is a hard fan base to aid the transition. Once could almost make a case for an “ABCD” keyboard just to ensure that potentially functionally-illiterate (or New Americanish) kids in the future know the dang proper order of the letters.

In the case of the other keys, I have one primary target: the caps lock key. Long, long past its utility, the overly-large (originally so you could put

Let’s change the

keyboard!Power Systems Corporation146 Charles Street Annapolis, MD 21401 USATel: +410.295.0177Fax: +510.217.3608 www.powersystemsdesign.com Editorial Director Alix Paultre, Editorial Director,Power Systems Design [email protected]

Contributing EditorsLiu Hong, Editor-in-Chief, Power Systems Design [email protected] Ryan Sanderson, IMS Research [email protected]

Dr. Ray Ridley, Ridley [email protected]

Publishing Director Jim [email protected]

PublisherJulia [email protected]

Production ManagerChris [email protected]

Circulation ManagementSarah [email protected]

Sale’s Team Marcus Plantenberg, [email protected]

Sydele Starr, North [email protected]

Registration of copyright: January 2004ISSN number: 1613-6365

Power Systems Corporation and Power Systems Design Magazine assume and hereby disclaim any liability to any person for any loss or damage by errors or ommissions in the material contained herein regardless of whether such errors result from negligence, accident or any other cause whatsoever.

Free Magazine Subscriptions, go to: www.powersystemsdesign.com

Volume 06, Issue 08

Fuji Electric’s Automotive Power Module for Hybrid and Electric Vehicles utilizes an Aluminum cooling solution, with a cooling fin that features an innovative structural design for a dramatic reduction in thermal resistance and a 70% reduction in weight compared to traditional Copper cooling structures. This lower cost alternative to Copper means higher performance and better fuel efficiency. We thought you’d like that.

For more information please visit our website: www.americas.fujielectric.com

Fuji Electric Corp. of America www.americas.fujielectric.com [email protected]

Using aluminum for superior cooling? What a refreshing concept.

Just another brilliant development by Fuji Electric.

6

POWERline


Semiconductor devices capable of handling higher levels of power are finding their way

into increasingly higher power ap-plications. To validate these new designs, researchers, fabricators and end-product designers need to be able to test experimental de-vices at higher power levels that increase their risk of exposure to electric shock and fire.

When Keithley Instruments in-troduced a source measure unit (SMU) instrument capable of sourcing up to 3000 V, its de-signers had to figure out a way to protect both users and other instruments in the test setup. Although the Model 2657A High Power System SourceMeter SMU instrument is designed to handle this level of power safely, other instruments configured into the test system typically are not. If a device under test faults to another terminal, a high voltage output could easily destroy a lower-volt-age SMU instrument. Figure 1 shows the Model 2657A-PM-200 Protection Module, designed to protect lower-voltage source measure unit (SMU) in-struments that are part of a test-ing configuration from damage by voltage sources that are greater than 220V. Keithley Instruments’

Keithley’s Model 2657A-PM-200 protection module

engineers designed this protection mod-ule for use in applica-tions where a device breakdown or other potential failure could connect the high volt-age output of an SMU instrument capable of sourcing up to 3000V to a lower voltage SMU instrument.

The connectors on the module’s high voltage side are rated for 3000 V, high enough for most power device testing, which typically is performed at 3x the rated voltage. The high-voltage triax connector has a special design that prevents a user from being exposed to high voltage. Additionally, unlike a typi-cal through-hole or surface mount connector, the high voltage triax connector is mounted in a routed channel in the PC board. This type of in-board mounting is necessary to ensure sufficient high voltage spacing and low leakage. The high voltage connectors are spread as far apart as possible and employ a driven guard concept that reduces both leakage and settling time.

The residual leakage current is less than 10pA, even at the full rated low voltage of 200V. Every terminal of the low voltage side

is protected from overvoltage, including the HI force and sense lines, and the LO force and sense lines. Solid-state protection de-vices shunt current away from the load in response to a surge that exceeds the breakdown voltage.

Grounding is critical. Safety standards require providing a sep-arate ground connection, because the shields of the triax cables are not considered a safe ground. The module’s case is constructed of metal and serves as chassis ground. The module comes with two grounding cables; both must be used. It must be able to sink more power to ground than the system could ever see from the instrumentation.

www.keithley.com

Best-in-class power density and reliability for highest performance

Infineon‘s PrimePACK™ high power module family presents a new member with best in class power density. The 1400A/1700V half bridge module offers a specially optimized concept for integration in wind turbine converter and solar applications. The most important benefits are improved thermal properties, low stray inductance and longest lifetime. With the introduction of the PrimePACK™ housing, Infineon established a standard for high power IGBT modules worldwide. Under permanent load in daily demanding use of renewable energy applications in rough environment with high humidity and salt content in the air the PrimePACK™ modules convince with their high reliability and robustness.

Key features: � Highest power density � Low stray inductance � Extended lifetime � Creepage and clearance distances made for 3.3kV modules � Complete portfolio with chopper and half bridge modules � RoHS compliant

Infineon Technologies Industrial Power · 1050 Route 22 · Lebanon · NJ 08833 Phone: 908-236-5600 · [email protected]

www.infineon.com/highpower

8

POWERplayer


By: Phil Scotcher, TDK-Lambda

Large organizations, particularly within the engineering and manufacturing sector,

are continuing to prove that investing time and money by offering placements to young and talented individuals is essential for a company’s economic growth. Apprenticeship schemes are an extremely effective way of helping companies and individuals achieve their goals.

TDK-Lambda UK has been offering paid career development work placements in the United Kingdom for several years. Providing a chance to employees, who might otherwise miss out on career progression, apprenticeship and trainee programs are two major cornerstones of our training and development processes.

One of our many successful engineers is Daniel Lawson; he began his career as an apprentice, gained a degree in electrical engineering in 2011 and even went on to be nominated for the National Apprenticeship Champion of the Year Awards in 2012. About his successful career development and progression,

Investing in tomorrow’s engineers

he expressed that it was the opportunity to ‘earn while you learn’ combined with the guaranteed career at the end that confirmed his decision to begin the course.

Another noteworthy story is the pupils of Blundell’s school wind tunnel project, who were last year announced the winner of the South West Engineering Education Scheme (EES) competition. Three students, with the help and guidance of Adrian Irwin, project performance manager, built the award winning real-life project. As a result, the students gained a high level of skills and technical knowledge, which can be used and built upon during the rest of their careers.

Most recently, continuing our investment in ‘tomorrow’s engineers’, we announced our involvement with the EDT’s (Engineering Development Trust) Year in Industry (YINI) scheme. This scheme is organized by the EDT, who run a range of work related STEM (science, technology, engineering and mathematics) courses and offer enrichment activities for 11-21

year olds across the UK.

Students participating in the scheme gain the chance to take part in industry led projects, industrial placements and specialized courses. With the help and expertise of professionals within the field, students are given a great opportunity, not only to gain knowledge and learn about an industry that is of interest to them but to attain skills that can be transferred into a career in science, technology, engineering or math.

Osamah Bayati, a student studying Computer Networks and Communications who completed his YINI program with TDK-Lambda in July 2013 offers another particularly successful story. Bayati investigated the potential impact of introducing Desktop Virtualization into the company. He worked with a number of providers and conducted various experiments that involved active employees working in a ‘virtualized’ environment.

www.tdk-lambda.com

By: Jonathan Eykyn, IHS Technology

The world market for power supplies that are used in medical applications continues

to grow strongly, thanks to continuing development in emerging regions as healthcare facilities are upgraded and expanded. Demand for medical equipment in Western Europe and North America remains lower, especially for medical imaging products but is projected to pick up in the coming years. Increasing demand for home health care solutions continues to help accelerate growth. Overall, the market for power supplies in medical applications is forecast to grow by $95 million from 2014 to 2018 with unit shipments growing by an average of 7.5% per year.

The market for power supplies used in clinical care devices such as ventilators, neonatal incubators and infusion pumps remains the largest segment of the medical equipment market. Investment remains high in this area, especially from the BRIC (Brazil, Russia, India and China) countries, as healthcare facilities are upgrade and expanded. A second wave of growth from Latin America and South East Asia is

Medical market driven by emerging regions

providing further expansion to the market. As a result, power supplies in clinical care devices are projected to account for almost two-thirds of the total medical power supply market in 2014. Owing to continued investment, demand in this sector is projected to remain high with market revenues calculated to grow by an average of more than 4% per year from 2014 to 2018.

The market for medical imaging devices (ultrasound, X-ray, CT and MRI scanners) is a relatively smaller portion of the total medi-cal power supply market in terms of unit shipments. This is due to the high cost of the equipment (an MRI scanner can cost upwards of $1 million) and the smaller ad-dressable market. The continuing pressure on healthcare budgets, especially in the developed mar-kets in Western Europe and North America as spending gets cut or frozen. There is a trend towards healthcare providers extending the replacement cycles of medi-cal imaging devices to increase cost saving. Demand for medical imaging devices from developing regions is increasing but remains low in relation to other medical equipment markets.

The positive of this is that due to the high price of the equipment and the complex power demands, there is less price pressure for the power supply solutions than in many other markets with high av-erage selling prices. As a result of this, the medical imaging sector is projected to account for a third of the medical power supply market revenues in 2014. The market is projected to grow by just over 3% per year on average from 2014 to 2018, again driven predominately by the BRIC regions as spending in developed regions remains low.

Finally, there is an increasing trend towards home healthcare, especially in developed regions as an attempt to reduce pressure on healthcare facilities. Whilst project-ed growth for medical equipment is high, many of these devices are battery powered, often with disposable batteries, reducing the power supply opportunity. Never-theless, there is a small but grow-ing market for power supplies for consumer medical devices, typi-cally for low power, power adapter solutions.

www.ihs.com

MARKETwatch


1110

DESIGN t ips

WWW.POWERSYSTEMSDESIGN.COM WWW.POWERSYSTEMSDESIGN.COM


By: Dr. Ray Ridley, President, Ridley Engineering

Board-mount power supplies use multilayer ceramics for both their input and output

capacitors. The inherently low ESR values lead to transfer functions with higher Q than converters using electrolytic capacitors, and this can lead to interesting effects when making measurements.

Many newcomers to the field of power supply design are very well trained in running simulations of their power supplies, and it is often a surprise to them to see how much the real world deviates from even the best thought-out models. More seasoned designers are less surprised by this, as they have long been aware that predictions of transfer functions must always be supported by good lab data. Figure 1 shows the schematic of a boost converter designed for a 13 V, 2 A load. The input source for testing the converter was a 20 A adjustable bench power supply connected via about 50 cm of cable to the input of the boost converter.

A large amount of capacitance for a boost converter, 88 uF, was

Source interaction with board-mount converters

used to provide a stiff voltage source at the input to the boost. Normally board-mount designers

will use much less than this since the ripple current into a boost converter is quite low.

Boost Converter Control Transfer FunctionsFigure 2 shows the measured transfer function of the boost converter from the control input of Figure 1 to the power supply output. An AP300 frequency response analyzer was used to make the measurements [1], and the design program POWER 4-5-6 was used to provide predictions of the transfer functions [2].

The measurements shown in red have a significant deviation from the predicted results. At first glance, it looks like something in the power stage components is making the Q of the measured boost filter resonance significantly lower than expected. The resonant frequency itself is also lower than expected. Moreover, the curve looks distorted. This is often indicative of too much drive at

the resonance, but adjusting the drive level did not make any difference to the measurement.

Figure 3 shows another measurement of the power stage transfer function, this time with a large electrolytic bulk capacitor added at the input of the boost converter. The new curve, shown in green, is much closer to the blue prediction. The filter is still more damped in the measurement, but this is to be

expected since the prediction does not include switching loss and other known loss mechanisms in the small-signal model.

Boost Converter Interaction with SourceMany years ago, Dr. Middlebrook showed how a converter would react with its input filter, or source, if the output impedance of the filter becomes higher than the open-loop input impedance of the converter itself. This is exactly what is occurring in the system of Figure 1. To assess the interaction properly, impedances

should be measured at the point shown to the left of the inductor in Figure 1. Measurement of these impedances using the AP300 analyzer is described in [1].

The measurement of the output impedance of the input source is shown in the red curve of Figure 4. The boost converter input impedance, also measured with the AP300, is shown in green. Clearly the two impedances violate the Middlebrook criteria,

Figure 1: Boost Power Converter with Lab Supply.

Figure 2: Measured and Predicted Control-to-Output Transfer Function for the Boost Converter

Figure 3: Measured and Predicted Control-to-Output Transfer Function for the Boost Converter with Large Bulk Capacitor Added.

Figure 4: Power Source and Connection Output Impedance Plotted Versus Boost Input Impedance

12

DESIGN t ips


and significant modifications to the control transfer function can be expected. The area of overlap of the impedances between 3 and 4 kHz is circled in yellow in the figure.

It is coincidental that the peak in impedance of the input source, cable, and input capacitor occurs right around the dip in impedance of the boost filter itself. This is not an uncommon event, though, and it is very important to remember that this interaction can easily happen with high-Q power stages. The low ESR of the MLC capacitors creates a sharp dip in the input impedance of the power stage, and avoiding overlap of the

impedances can be almost impossible.

The blue curve of Figure 4 shows the impedance of the source modified by the presence of a very large 10,000µF capacitor. The green curve is now well above the output impedance of the source, clearly showing why the measured transfer function in Figure 3 is very close to the prediction.

Notice that there is about 12 dB of separation between the blue and the green curves of Figure 4. This means that interaction could have been avoided by adding a capacitor about 4x smaller (12 dB), or 2500µF. This

is an amazingly large value of capacitance needed for a low ripple converter like a boost. Most designers do not have the luxury of adding this kind of value, and they have to just accept a more complex system model.

The interaction of impedances does not mean that the system will be unstable -- that only happens if the output impedance of the source exceeds the closed-loop input impedance of the boost converter. The point of this article is not to suggest that the system may go unstable for board-mount converters, but to show that interactions between converters and filters in the system are quite likely to occur. Simple two-state models of the individual converters will not suffice to explain the observed measurements, and these effects should be included when trying to optimize feedback design.

Observing Interactions from Other Transfer Functions. Sometimes it is simply impossible to break circuit paths to get at the needed impedance measurements. If you suspect this kind of interaction, however, there are other ways to observe problems. Figure 5 shows how to set up the AP300 to measure the control-to-input voltage transfer function. If there is an overlap of impedances, a significant peak of this transfer function will be observed as shown in the green curve. In some systems, such

Figure 5: Control-to-Input Voltage Transfer Function Showing Significant Peaking at 3 kHz.

as current-mode control for a buck, this is the only place that the interaction can be observed, by that is a deeper topic which is too involved to present here.

The power of interactionIn this article, is has been shown that board-mount power supplies can have a strong possibility of interacting with their power sources and other components around them. While this may not necessarily lead to instability in the system, you should at least be on the alert for observing significant modifications to the expected transfer functions. Regardless of how simple your

power supply seems to be, or how much a chip vendor insists it is not necessary for their part, you should always make measurements of the loop of your power system to guarantee stability.

www.ridleyengineering.com

References1. AP300 Application Notes

and Videos, http://www.ridleyengineering.com/analyzer.html

2. POWER 4-5-6 Design Software, http://www.ridleyengineering.com/software.html

3. Join our LinkedIn group titled “Power Supply Design Center”. Noncommercial site with over 4800 helpful members with lots of theoretical and practical experience.

4. See our videos on loop testing and power supply design at http://www.youtube.com/channel/UC4fShOOg9sg_SIaLAeVq19Q

5. For power supply hands-on training, please sign up for our workshops at http://www.ridleyengineering.com/workshops.html

8 Channels, 12 Bits

Who’s doin’ that!teledynelecroy.com/8channel

High Definition Oscilloscopes

TLEC_halfpage-green-product7.5x5.5.indd 1 9/22/14 4:05 PM


1514

COVER STORY



Extending battery life in wireless medical devices

By: Jehangir Parvereshi, SiTime

Key to the rapid growth of wearables is reduced device size and longer battery life

Wireless medical devices are becoming increasingly

more prevalent for remotely monitoring and logging vital signs to assist in the detection and treatment of diseases and medical anomalies. An example is shown in Figure 1. Wireless body sensors upload vitals via an Internet hub or personal server such as the patient’s smart phone. To continuously monitor and upload vital data, wireless medical devices need to maintain long-term connectivity to the cloud. Key to continued rapid growth of medical wearables is reduced device size, longer battery life and ubiquity of smart phones.

Wearable medical monitoring devices are designed to collect and compress data (metadata), send it to the cloud via Internet hub devices in short bursts, and then go to sleep to conserve power. Battery life depends in part on the power consumption of the wireless radio and interface protocol deployed in the

design. Designers of wearable sensor devices can choose from the following PAN (Personal Area Network) low power wireless communication standards:• ANT• ZigBee• Bluetooth® low energy

(BLE)

Which wireless protocol should the designers of such wireless medical devices deploy? See the sidebar for more information on how these protocols meet wireless requirements.

Which Wireless Standard has the Lowest Power?Independent studies comparing the top three wireless standards have shown that BLE has the lowest power consumption in a cyclic sleep scenario typical of a network of wireless body sensors [1], [2]. The cyclic sleep scenario is a typical use case of these battery powered devices wherein the device core is shut down for a pre-set time called “sleep time” typically in the range of 2 to 10 seconds and “woken” when it needs to transmit vitals

during a short burst lasting a few milliseconds. This translates to a low duty cycle activity scenario, which leads to lower average power consumption.

In one experiment, average power consumption was measured across various sleep intervals on three wireless modules [1]. The results of the power consumed across the various RF modules, shown in Figure 2, indicate that the BLE protocol consumes the least amount of power compared to ANT and ZigBee irrespective of sleep intervals. The data also show power consumption scales inversely with sleep interval across all three RF standards in a cyclic sleep activity scenario.

Given the ubiquity of the smart phone and its native support for Bluetooth 4.0, BLE is ideally suited for wearable medical devices. In certain medical environments, where smart

phone use is prohibited, the use of a BLE-to-Internet bridge may be used as an alternative. BLE in a Medical Device A typical wireless medical device comprises a low power 32-bit MCU interfacing to biometric sensors and a RF front-end SoC (system on chip) as shown in Figure 3. The low power MCU

typically serving as sensor data aggregator sends vitals to the BLE RF front-end via an I2C or UART interface, and runs off the following clock sources:-12 MHz crystal-Frequency tolerance: +/- 30 ppm for 0 to 70°C-Used for clocking ARM Cortex-M3 core and peripherals-32.768 kHz crystal-Frequency tolerance: -200 ppm for 0 to 70°C-Used for real-time clock(RTC) and watch-dog timer

The BLE RF front-end implements

the Bluetooth-4.0 PHY layer and BLE Link-layer including GATT profiles (glucose, temperature, blood pressure, etc.) and runs off of two clock sources: -24 MHz crystal -Frequency tolerance: +/- 20 ppm for 0 to 70°C-Used for base-band processing and RF 2.5 GHz synthesis -32.768 kHz crystal

Figure 1: U-Healthcare system overview

Figure 2: Power consumption of the three wireless standards vs. sleep interval

Figure 3 Block diagram of a wireless medical device

1716

COVER STORY



-Frequency tolerance: -200 ppm for 0 to 70°C-Used for sleep clock timing

Empirical measurements have shown power consumption of a BLE medical device is inversely proportional to the time it spends in the “sleep” state, and the sleep clock accuracy (SCA) of the 32 kHz clock used to time this “sleep” state has a direct impact on the battery life of the device. To understand this, let’s briefly review how a BLE slave (patient’s medical device) and a “paired” BLE master (internet hub) establish a connection event. A scope capture of the dynamic IDD timing of a BLE

slave is representative of the connection event timing profile of a BLE device as shown in Figure 4.

Note that the BLE standard calls out “sleep time” by the term “connection interval”; range: 7.5 ms to 4s. The connection event is the “ON” time during which certain functional blocks of the device wake up and stay active for short periods in the range from 0.08 ms to 1.3 ms.

The following link parameters are negotiated by the BLE slave with the BLE master during every connection event:-Connection interval (sleep time)

-Sleep latency-Supervisory timeout

A sleep latency value of N (N < 500) extends the sleep time by N connection intervals. Example: connection interval = 2 s and sleep latency = 5 extends the sleep time to 2 x 5 = 10 seconds. The link parameter, supervisory timeout is used by the master to terminate the connection if a “paired” slave does not respond within an agreed upon time period; range: 100 ms to 32 s.

To further understand the impact of the 32 kHz sleep clock accuracy (SCA) let’s review the link-layer (LL) messages

exchanged between a “paired” master and slave device while establishing a connection event.

During every connection event, the master sleep clock accuracy (master SCA) is communicated to the slave. The slave

determines when to wake up during consecutive connection events based on a combination of the following:-Last negotiated connection interval -Master SCA -Its own sleep clock accuracy

(slave SCA)

Due to inaccuracies of the sleep clocks involved, there’s a certain level of uncertainty in the time when the slave wakes up from sleep to listen to packets from the master. Due to this uncertainty, the slave wakes up and starts listening (receiver turned ON) earlier – a process called “window widening”. As per the Bluetooth 4.0 specification volume 6, this window widening or early turn on time, ΔT is given by the following formula:ΔT = windowWidening = ((masterSCA + slaveSCA)/1000000)*(last connection interval))Where: -masterSCA is sleep accuracy of the master 32 kHz sleep clock in

Figure 4: Connection event Timing Profile of a TI CC2541 BLE SoC with IDD current scope measurements

Figure 5: Measuring RX Window width on a BLE Slave with varying sleep clock accuracies

Table 1: Impact of sleep clock accuracy (SCA) on the width of slave RX window

1918

COVER STORY



ppm-slavesSCA is sleep accuracy of the slave 32 kHz sleep clock in ppm-last connection interval is the last successful established connection interval in seconds

This “window widening” directly translates to the width widening of the slave RX window shown in Figure 5. In order to quantify the RX window width across various SCA settings, we measured the current profile of a BLE slave in a test setup similar to the one referenced in the TI BLE Application Note [3].

The link parameters programmed

in to the slave:-Connection Interval = 2 s-Latency = 0-Supervisory timeout = 32 s

The 32 kHz crystal on the BLE slave was replaced with a high accuracy 32 kHz 5 ppm TCXO (SiT1552 from SiTime); slaveSCA = 5 ppm. A vendor provided GUI was used on the host PC to sweep the masterSCA values: 20 to 500 ppm in eight steps. For each masterSCA setting, the RX width during a connection event (ON time) was measured.

The RX width measurements listed in Table 1 correlate with the equation for window widening –

Table 2 Tighter slave clock accuracy reduces early ON time

width increases proportionately as the combined SCAs.

Extending Battery Life Due to the use of micro-power MCUs which turn on during short bursts of a few milliseconds, most of the system power during ON time is dictated by the BLE RF front-end in a wireless medical device. As explained earlier, 32 kHz sleep clock inaccuracies cause the BLE radio receiver (RX) to turn on earlier and stay on longer to avoid missing packets from the master whereby increasing the power penalty.

Table 2 shows that tighter slave clock accuracy reduces early ON time, ΔT thereby reducing power consumption. Let’s compute battery life extension ratios for two distinct 32 kHz sleep clock accuracies.-TON = 3 ms (typical)-for 5 ppm sleep clock (SCA = 5) and 20 seconds sleep time, ΔT1 = 0.1 ms -for 200 ppm sleep clock (SCA = 200) and 20 seconds sleep time, ΔT2 = 4.0 ms

Device power dissipation is directly proportional to total ON time (ΔT + TON). Battery life extension ratio is inversely proportional to device power dissipation:P2/P1 = (ΔT2 + TON)/(ΔT1 + TON) = 2.26 times

The plot in Figure 6 shows the achievable battery life extension

Figure 6: Battery life extension ratio with a 5 ppm 32KHz TCXO over a 100 ppm and 200 ppm XO Figure 7: Optimized architecture of a medical device using SIT1552 TCXO in lieu of

traditional 32 kHz crystals

with a 5 ppm sleep clock over a 70 ppm and 200 ppm 32 kHz clock source. For instance, for a sleep interval = 20 seconds a 5 ppm 32 kHz sleep clock can achieve > 2x battery life extension over a 200 ppm sleep clock.

Power Optimized Medical DevicesDesigners of wearable medical devices now have an alternative higher accuracy 32 kHz sleep clock to accurately wake-up after extended sleep times with optimized radio RX window widths.

In practice, a small form factor

(1.5 x 0.8 mm) 32.768 kHz TCXO, such as SiTime’s MEMS-based SiT1552 with a +/- 5 ppm frequency tolerance across -40° to 85°C is available as an alternative to the 200 ppm 32 kHz crystal-based sleep clock sources used in past designs[4]. An optimized version of the medical device architecture using the SiT1552 TCXO is shown in Figure 7. The SiT1552 TCXO can drive multiple CMOS loads and is shown eliminating both the bulky BLE sleep clock crystal and the MCU RTC 32 kHz crystal, saving precious board real estate. Designers can now leverage compression and transmit

vitals in short bursts only when requested while keeping the device in its lowest power sleep state for extended periods and potentially achieving up to twice the battery life extension.

www.sitime.com

References

1. A. Dementeyev, S. Hodges, S. Taylor and J. Smith, "Power Consumption Analysis of Bluetooth Low Energy, ZigBee, and ANT Sensor Nodes in Cyclic Sleep Scnerio," in IWIS, Austin, 2013. 2. R. Tabishi, M. B. Adel and F. G. A. Taouti, "A Comparative

Analysis of BLE and 6LoWPAN for U-healthcare Applications," IEE GCC, Quatar, 2013.

3. Texas Instruments, "AN092 : Measuring Bluetooth® Low Energy Power Consumption," TI, Dallas, 2012.

4. SiTime Corp, "SiT1552 Data Sheet," http://www.sitime.com/products/datasheets/sit1552/SiT1552-datasheet.pdf SiTime Corp, Sunnyvale, 2014.

2120

BATTERY CHARGING & MANAGEMENT



Get a constant output switching with a +5V input and a single-cell battery

By: Don Corey, Maxim Integrated

Powering portable devices often involves switching between sources

Some portable applications need to be powered up from an external +5V wall

adapter supply and still require a +5V system voltage when in battery-backup mode. This design provides a simple method of switching between the external +5V supply and a rechargeable single-cell Lithium-ion (Li+) battery. The design will still maintain uninterrupted +5V to the application circuitry.

Three key circuit functions are needed:1. An efficient Li+ battery charger2. An efficient boost converter to convert the battery voltage to +5V3. A low-loss switchover circuit that automatically switches between the main DC power and the backup Li+ battery

As shown in Figure 1, U1 is a high-performance battery charger (MAX8903) capable of supplying up to 2A to charge a single-cell battery. Resistors RIDC and RISET set the DC-input current limit and charge-current set points,

respectively. Since the SYS output (pins 23 and 24) is not used, the charge current will be constant and not dictated by the load current.

Q1 and Q2 are dual PNP transistors, available in an SC74 package. These transistors are used with the p-channel FETs, Q4a and Q4b, to form ideal low-loss ORing diodes. The output of

the ORing diode configuration is then fed to a high-efficiency boost converter, U2 (MAX8815A). When the +5V input voltage is present, U1 is charging the battery. Q4a conducts, as the voltage on R2 provides a negative bias with respect to Q4a source voltage. The voltage on the base of Q2b is higher than the voltage on the emitter of Q2a transistor. Consequently, Q2a is turned off

and Q2b is turned on because enough base current flows thru R3 to ground. Since Q2b is now fully on, the voltage at the Q2b collector is very close to the output voltage. Q4b is also biased off as the voltage difference between its gate and source pins are close to zero. When the +5V source is removed or lower than the battery voltage, circuit operation is identical to the above description for Q4b, Q1a, Q1b, R4, and R1.

U2 is a highly efficient boost converter that delivers over 1A of continuous current. As the input voltage to U2 has a range of 3.0V to 5V, U2 still provides a highly regulated 5V output even when the input is +5V.1

Figure 1: This design switches between the external +5V supply and a rechargeable single-cell Li+ battery to provide a constant +5V output.

Figure 2: This design also switches between the external +5V supply and a rechargeable single-cell Li+ battery to provide a constant +5V output.

There are advantages and disadvantages to placing the boost in the power path of the +5V wall adapter. The disadvantage is with the efficiency. The boost converter will incur more power losses versus a circuit that simply uses a FET switchover circuit to switch between the wall adapter voltage and the boosted battery voltage. There is, however, a nice advantage of using a boost at the output: it will regulate the +5V output and account for IR drops in the adapter cable. Additionally, placing the MAX8815A at the output provides short-circuit protection. Figure 2 shows a way to implement this circuit with fewer parts. This approach uses the

SYS output of the MAX8903 as the input to the MAX8815A boost converter. This method eliminates transistors Q1 and Q2 as the switching elements, and uses the internal switchover circuit of the MAX8903.

Lowering the part count comes with trade-offs. The main performance drawback to this approach is lower efficiency. When the main input is connected, the MAX8903 regulates the output to 4.4V or 4.325V depending on the part variant. When the battery voltage is at the VCHG point, the voltage regulates the SYS output to one of these voltages. Refer to Figure 4 from the MAX8903 data sheet for the VSYS voltage curve when the battery is charging. A second trade-off is with the battery charge current—it is load dependent. This means that the charge current is the difference between the input current limit, which is settable up to 2A, and the load current. As such, at full output load it will take a longer time to charge the battery versus when the output is lightly loaded.

There is, finally, a good advantage to this approach: the input operating range of the MAX8903. The input voltage range is specified 4.5 to 16V with 20V input protection. The circuit in Figure 1 is limited by the 5.5V maximum operating input voltage of the MAX8815A.

www.maximintegrated.com

2322

SERVING THE GRID



Automating ecological energy generation

By: Scott Ludwig, Progea

Eco-sustainable projects that get the most out of resources are at the basis of modern energy policies

Agip’s Italian electric energy production uses fuel obtained from the mineral

oil extraction process that takes place in the Oil Center of Torrente Tona di Rotello, in the province of Campobasso. The electric energy produced here is used to advantage in the national electricity distribution main controlled by ENEL (the Italian Electricity Board).

The Agip plant has been extracting mineral oil for several years. This oil is subsequently used in refining processes. Extraction leads to the presence of well gas, which is usually unsuitable for use as it is unless specially designed machines are employed to enable combustion. The gases at the well outlet are a mixture of natural gas, other fuel gases, water vapor and so forth. Until only a short while ago, these gases were burnt in torches. They were dispersed and wasted in those flames that we often see burning at the top of gigantic pylons near extraction plants.

It was evident that sooner or later the Agip managers would have wanted to find out how this potential could be utilized particularly in times like these, when energy is precious and its recovery goes hand in glove with those environmental policies about which public and private sectors are finally becoming aware. In cases like these, the experience and skill of partners when research is carried out to identify the best solution is of fundamental importance. This is why Cefla Scrl was contacted as this group works in various industrial fields, amongst which the energy and co-generation sectors.

For the technicians in Cefla’s Plant Division, the target was to use the extracted fuel gases, filter them and make them fit to fuel the largest possible number of generators and create a profitable power station. Cefla proved that it was able to provide Agip with the “turnkey” project, covering the building works to the generators, the automation and monitoring software to plant management

and the actual staff members.

The fully successful results obtained now allow Agip to use a 20,000 kW power station where electricity is produced by a system formed by 8 generators driven by engines powered by the very same gas that was previously “burnt” in the atmosphere. The power station is run by an avant-garde automation system based on a PLC network in Profibus FMS and two PC stations based on the Scada Movicon system for supervision and monitoring purposes.

Structure of the power stationThe power station designed, built and run by Cefla includes a network of eight 16-cylinder engines manufactured by the Norwegian company Bergen. Each one is connected to a generator, which produces around 2,600 kW. The engines are the internal combustion Otto type and are fuelled with the well gas extracted at the same time as the oil, plus the process gas, i.e. the gas from the three-phase separators in the Agip plant.

The utilities correlated to each electricity production unit need to be monitored. These utilities include the engine oil feeding circuit, the cooling circuit using water with glycol additive, the air compressors, the filtering system, the ventilation circuit of the engine room, the gas and gas vent on-off valves, the safety devices, the automatic engine stopping and starting mecha-nisms (see Figure 1). Besides monitoring the generating plants as they operate, the system also automatically controls the electric energy produced and conveyed to the ENEL network, operating the IG circuit-breakers on each generator and the IR mains circuit breaker on the backbone line that links to ENEL’s national distribution network. Besides

being conveyed to this latter, the energy is also used in the power station itself where it powers the electrical users of the plant auxiliaries.

Automation architectureEach of the eight generating plants is monitored by an equal number of graphic synoptics like the one shown in Figure 2. The architecture of the automatic system that controls the entire production plant has been designed to ensure reliable operation and to integrate the components.Cefla Impianti chose two partners for these automation techniques: Progea with the Movicon software system for the Scada platform and Siemens for the programmable logic systems.

The following factors were considered as fundamental when

the system was planned: • easy maneuvering for the

controls and adjustments;• easily identified alarms;• separated circuit equipment

or various systems to

Figure 1: Main page of AGIP’s mineral oil extraction plant in Torrente Tona. Special objects called “Embedded synoptics” are used to represent the real status of the project.

Figure 2: Each of the eight generating plants is monitored by an equal number of graphic synoptics

2524

SERVING THE GRID



prevent maneuvering and/or interpreting errors;

• correct and immediate identification of the emergency equipment plus their protection to avoid maneuvering errors;

• easy operation when it comes to servicing and replacing components.

The monitoring system of the electricity main provides the following functions:• Acquisition and control of

the signals to and from the field;

• Display and historic cataloguing of the alarms;

• Management of local and remote controls;

• Communication with external units;

• Functional calculations (compensated measurements, etc.);

• Adjustment;• Monitoring and management

of the electricity main;• Autodiagnosis.

The PLC-based monitoring systemsCefla Impianti uses a network of Siemens PLCs in a mixed configuration, featuring a main network based on the PROFIBUS-FMS standard with redundant loop cable in optic fiber and a secondary network of the Siemens MPI type to connect the self-standing monitoring devices of the generating units.

An S5-155H PLC with redundant configuration installed in the main control room handles the common functions of the entire power station plus the functions that interface with ENEL’s network. An S7-400 PLC handles the operation of the auxiliary

users and monitors the electricity production part for each generator. Moreover, each engine has its own S7-315 monitoring unit.

The main monitoring PLC consists of 5 racks, 2 main ones and 3 extensions. Two CPUs, one for each main rack, guarantee operating redundancy. Both CPUs control the process together while the user program, the data blocks and the contents of the process images are kept up to date by the coupling lines. The system conducts the self-test functions every 5 ms. If one of the CPUs breaks down, the system continues to operate correctly with the other processor.

The redundancy concept also applies to all the critical I/O of the system, where two outputs (one for each partial central device) or three inputs (one for each partial central device and one for the extension device) are used for each signal. If faults occur in one of the redundant boards, they are localized and passivated until successive replacement, thus guaranteeing continuous service. The less critical I/O signals are handled in the shared mode by means of the boards installed in the extension device.

Main PROFIBUS-FMS networkEach generating plant is provided with a series of users, each of which is centralized and common to all plants (see Figure

3). As hardware backup, optic fiber cable is used (62.5-125) in the redundant loop configuration with PROFIBUS FMS protocol at a speed of 1.5 Mbaud.

The communication processors in the PLCs, the communication boards in the PCs and the optic connection module are an integral part of the communication network.

The communication system provides monitoring procedures for the information in the network in order to prevent this from being subjected to alterations as it transits. The network architecture is the Master/Master type and the network traffic is handled by a “token” that passes from one participant to the other in cycles. The participant that possesses the “token” is enabled

to transmit information to the others.

A network of electric parameter indicators connects the modules that acquire the electrical parameters located in the various monitoring panels and the main monitoring PLC that acts as a Master. RS 485 communication with MODBUS-RTU protocol at a speed of 9.6 kbaud is used as hardware backup. The information obtained from the individual modules is send to the respective engine monitoring PLCs.

SupervisionPlant supervision is based on a Scada Movicon software platform. Cefla has been using Movicon as software platform for its automation applications for quite a long time, both in the Plant Division and in

Figure 3: Each generating plant is flanked by its auxiliary users, and all the functional parameters are represented by animated objects

Figure 4: The synoptic that represents the electricity network of each individual generating plant

other operating sectors of the group. The decision to do this was based on Windows NT being used as standard for the automation systems and this led to selection of a SCADA platform able to provide potential, flexibility and compliance with the Microsoft standards (thus assuring reliability and easy use).

Flexibility and the ability to inter-operate with the Microsoft Office line of products was particularly appreciated. When it comes to the methods applied in Cefla’s software planning departments, all this considerably speeds up the time it takes to develop new applications. Movicon also proved to be fully satisfactory in a critical configuration like the Agip plant in the Torre Tona Oil Center, a configuration with around 20,000 Tags to supervise.

Plant supervision thus includes two redundant PC stations, each of which is connected to the plant by the Profibus FMS optic fiber network able to display the process parameters and allow the operator to control the system. One station is installed in the control room of the electric energy generating building while the other is in the control room of Agip’s Oil Center. All the parameters and electricity values produced by the plant are monitored and historically catalogued (see Figure 4).

In addition to the two supervision

26

SERVING THE GRID


stations, each monitoring board has an Operator Panel for local display of the alarms and analogue values in the PLCs.The supervising system provides the following functions:• It displays the operating

statuses of the plant;• It acquires the commands

given by the operator;• It displays alarms;• It displays trends;• It manages historic archives.The system software carries out all the monitoring, diagnostic and control functions, thus providing the operator with everything he needs to operate the plant on a continuous yet simple basis.

Connections to the supervising system can also be made from remote stations since the operator station, which is located in the control room of the electricity generating building, is linked via modem to the telephone line.

Graphic SynopticsParticular care was taken when the synoptic masks were created as the operators to run the plant use them. Here, the strategy was based on simple use for the operators while speeding up the development phase. The planning engineers in Cefla’s Plant Division decided to use the standard tool bar for surfing through the synoptics of the supervisor. Each page consists of two synoptic windows, one with graphic representation of the

area in question and the other with the tool bar for surfing the system which self-configures to suit the synoptic selected.

There is a page with the general layout of the plant in simplified form. This has been divided into zones characterized by the main components of each and linked together by the main connection lines (electric cables, ducts and pipes). This mask allows the operator to switch to the next synoptic masks by simply selecting the corresponding zone with the mouse. A large number of synoptics allow the plant values to be analyzed. The Historic Trends enable an accurate analysis to be made of all the basic parameters of both the utilities and electricity users.

The other graphic masks represent the synoptics animated with the process lines and equipment, plus the relative instruments. Each of these has been set up so that it displays the values of the measurements of each individual analogue variable, the status of the equipment (pumps, valves, electric lines, etc.) and the alarms concerning analogue or digital variables.

AlarmsAlarms are displayed in chronological order. The operator has a command so he can recall already identified

alarms that are still activated (from the less recent to the most recent). All the events are recorded and stored in Historic Log files that the operator and service engineer can analyze with the selection criteria desired (by date, by priority, by event, etc.).

A synoptic with Operating Messages shows the status of the most important signals in the plant by displaying their corresponding messages in text format. Along with an indication as to the date and time, these operating messages are memorized in the Historic Log files whenever the status changes.

Plant Time synchronizingThe Movicon supervising system handles and synchronizes the time settings of the system for all network participants. In particular, one of the two Scada stations acts as master and, thanks to the integrated functions, sets the time and date of the operating system of the second station and of all the PLCs and Operator Panels. Thanks to Roberto Sentimenti (Cefla) and to Dr. Bortolato (Agip Petrols)

www.progea.com

A 4.5kV IGBT/Diode chip set for HVDC transmission apps

By: Thomas Schütze, Infineon Technologies

The device combines very low on-state voltage losses with fast turn-on behavior

The latest 4.5kV IGBT/diode chip set from Infineon has been developed and

optimized for HVDC applications. It features very low on state voltage losses combined with fast turn on behavior for high current, high voltage and high robust short circuits behavior. High robustness will be demonstrated using HDR technologies for IGBT and diode. The 4.5kV class supplements the already existing high voltage classes of 3.3 kV and 6.5 kV. The chip set will be available in two different housings.

The first is a highly insulated 6.5kV module housing, offering 10.2kV isolation capability and corresponding creepage distance and clearance distance as requested by the harsh environment of traction applications with DC link voltages in the range of 2500-3000V. The second chip set is designed for the IHV-B housing, the successor of the well-known and worldwide applied IHV-A module. This module addresses industrial applications like medium voltage drives and the wide field of

High Voltage Direct Current (HVDC) as well as flexible-AC-transmission-system (FACTS) applications. The module is shown in Figure 1.

These IGBT-based voltage source converters (VSC) will play an important role for future HVDC systems – in contrast to the well-known thyristor-based grid-commutated high-voltage DC transmission. IGBT-based solutions are independent active- and reactive-current control due to the turn-on and turn-off capability of the IGBT. Additionally, they show a superior performance in case of AC-grid faults.

For high voltage applications a large number of semiconductors used to be connected in series and simultaneous switching with high accuracy had to be ensured. In order to facilitate this demanding design a multi-level VSC – Modular Multilevel Converter MMC – for high voltage applications like HVDC

and FACTS was proposed. The switching frequency of individual IGBT modules can be reduced in HVDC applications. Therefore low on-state losses are of special interest in order to reduce the overall power consumption.

IGBT and diode structureThe IGBT trench technology provides low on-state losses due to the carrier accumulation effect between the cells together with an optimized cell pitch, and an optimized channel length as well as channel width designed for high blocking voltages. As a result, the trench technology offers a feasible way to influence the charge carrier concentration below the cell within a wide range compared to the standard planar technology. Figure 2

Figure 1: The 4.5kV FZ1200R45HL3 module


POWER SEMICONDUCTORS

28



Amongst others, the channel width is one possible IGBT parameter for adapting the turn-on behavior to a predictable failure event. In case of an

increased channel width a rapid turn-on performance can be achieved. At the same time, however, the increased channel width is suffering from short circuit capability due to an increased short circuit current. Hence, a compromise between turn-on performance and short circuit capability has to be found. Alternatively, the vertical structure of the IGBT is enhanced to fulfill both of these requirements.

Short circuit capabilityIn order to prove the short circuit type 1 capability of the IGBT tough conditions such as VCE=3000V, VGE=17V and T=125°C have been applied. 9500A, nearly 8 times of the nominal current, have been switched off. The vertical IGBT structure has been optimized to prolong the lower limit of short-circuit time until device failure. In Figure 4 a short-circuit waveform is shown. The short-circuit event can be handled by the IGBT

module FZ1200R45HL3 and a reliable turn-off is granted even after a short-circuit duration of 10µs.Figure 3A

Figure 3B

Figure 3cFigure 3: Typical waveforms at 2800V / 1200A, 150µH, 150°Cturn-off: VCE=400V/div, IC=150A/div, Rgoff=5.1Ω, VGE=5V/divtu rn -on : V CE=350V/d i v, I C=300 A/d i v, Rgon=1.2Ω, VGE=5V/divreverse recovery: VCE=500V/div, IC=500A/div, Rgon=1.2Ω

depicts the schematic cross sections of the 4.5kV IGBT/diode. For the edge termination for both devices a VLD structure (varied lateral doping) has been applied. In combination with the vertical HDR structure this leads to an extreme high turn-off robustness of the IGBT and commutation robustness of the diode, respectively, due to the reduction of dynamic avalanche phenomena during the switching sequence.

Electrical performance - Static characteristicsTo realize low on-state voltages for the 4.5kV IGBT the well-known trench technology from the 6.5kV device platform has been adapted. This includes a suitable base material, an adapted field stop and an optimized cell design that results in the best-in-class on-state characteristic for 4.5kV devices. At 1200A, the nominal current of the FZ1200R45HL3 module, a typical VCE(sat)=2.35 V at 25°C, VCE(sat)=2.9 V at

125°C and VCE(sat)=3.0V at 150°C temperature are realized. The EC diode exhibits an almost neutral temperature coefficient at nominal current of 1200A and a typical forward voltage drop in the range of Vf≤2.5V in the temperature range of 25°C ≤ T ≤ 150°C.

Dynamic characteristicsSwitching waveforms at nominal conditions, i.e. VCE=2.8kV, IC=1200A and T=150°C are shown in Figure 3. Under these conditions a soft turn-off behavior for a commutation inductance of 150 nH can be seen. The VCE does not exceed 3.4kV. A soft turn-off is also ensured for harsher conditions, i.e. higher stray inductances, higher currents and operation temperatures down to -40°C. Typical turn-on and reverse recovery waveforms are

depicted as well. They reveal a very smooth IF tail gradient.

Switching at high voltage and high currentFor HVDC applications it is important that in case of a failure event the IGBT shows a rapid turn-on behavior at high voltage and high current in time. The device’s ruggedness under such conditions beyond the RBSOA limits has been evaluated.

Figure 2: Schematic cross section of the IGBT (left) and EC diode (right) with HDR and VLD edge termination

How stable is yourpower supply?

Easily determine stability using the Vector Network Analyzer Bode 100 in combination with the Wideband-Injection Transformer B-WIT 100.

Measure loop gain, plant transfer function, phase margin and gain margin from 1 Hz to 40 MHz.

Gm

𝜑𝜑𝜑𝜑m

Smart Measurement Solutions®

140829_Stability_third_seminars_2.indd 1 2014-09-30 16:36:41

30



Robustness of IGBT and diodeFor HVDC applications as well as for traction applications a high over-current turn-off capability for IGBT and diode is improving the systems reliability.By applying the HDR concept the impact of the termination system on the IGBT robustness can be neglected. Only the cell design constitutes a limiting factor. The trench structure allows for a further reduction of the source length of the IGBT. Due to the fact that the current density decreases inversely proportional to the source length, the latch-up immunity of the trench IGBT is effectively improved and excellent turn-off ruggedness is obtained. This is demonstrated by switching five times the nominal current without severe oscillation on current or voltage signals.

In addition to a low on-state

voltage the new 4.5kV EC diode reveals low dynamic power losses in combination with a very high robustness. The diode recovery has been tested for a 200A nominal current module with Pmax≥4MW without destruction.

Surge Current capabilityIn an event of failure, e.g. short circuit

in the power transmission line, fault conditions such as high surge currents can occur during diode operation. Therefore, the ability to withstand high surge currents is an important criterion for the usability of the module. Sufficient surge current capability can be realized by an optimized vertical design resulting in a low VF together with the HDR concept. For a module with IC=1200A a typical IFSM value of about 10kA can be reached which corresponds to a I2t of about 500 kA2s at 125°C temperature or 460 kA2s at 150°C.

Cosmic radiation robustnessThe 4.5 kV IGBT and emitter controlled diode is designed for high robustness against cosmic radiation. The vertical device structure shows low electrical field strengths at typical DC-link voltages. The typical FIT rate, number of failures in

Figure 4

109h operation hours, for the FZ1200R45HL3 module at ~3kV DC-link voltage has been determined as 100 FIT. Besides the steady state situation during blocking the DC-link voltage the cosmic radiation robustness under switching operation has also been considered. Simulations confirmed that an additional dynamic FIT rate can be neglected for dV/dt up to 2kV/µs due to a limited electric field within the device.

SummaryThe newly presented 4.5kV trench field stop IGBT and emitter controlled EC diode have been designed for industrial applications and, in the IHV-B package, especially for HVDC applications. The IGBT and diode performance features a very low on state voltages and fast turn on switching behavior of the IGBT especially for high voltage and high current beyond the standard conditions. Simultaneously, the FZ1200R45HL3 module shows a high short circuit performance. Furthermore, an extremely high IGBT and diode robustness during over current turn-off is demonstrated. The new devices are designed for an operation temperature of up to 150°C. These features were realized by adaption of the trench cell design as well as the vertical structure of the 6.5kV IGBT using the HDR technology.

www.infineon.com

Smart PFC and DC/DC converter system offers optimum efficiency

By: Dr.Bernhard Strzalkowski, Analog Devices

Digital power is becoming increasingly popular

The efficiency improve-ment of power convert-ers is one of the major reasons why digital

power is becoming increasingly popular. For specific requirements, digital control allows using the best fitted control strategy and comfortable, intricate tweaking of efficiency. This means the power supply can operate in multiple topologies and modes. This is something that cannot be realized by an analog control unit, which only operates in single mode. The power efficiency of AC/DC and DC/DC converters is a non-linear function of their output load level. Therefore, variation of intermedi-ate bus voltage level (IBV) as well as of converter topologies helps increase efficiency for different out-put power level. This paper shows a smart system consisting of an AC/DC PFC- and DC/DC system providing 230Vac to 12Vdc conver-sion with power efficiency self-tun-ing algorithm. The key approaches for optimum system efficiency are dynamic optimization of interme-diate bus voltage (IBV) and phase shedding.

Positioning PFCOff-line power supplies are widely

used in every kind of computer, communication, and home ap-pliance equipment. Power-factor-correction (PFC) control schemes have been developed to comply with the EN61000-3-2 standard for input line current harmonic components. In general, a PFC converter will result a lower effi-ciency and higher harmonic dis-tortion under light load operation conditions. With the continuously increasing power efficiency target by 80 PLUS [1], U.S. Energy Star [2] and Climate Savers [3], it becomes a design challenge for AC-DC PFC technology to improve its power quality as well as efficiency over a wider operating range [4].

Typically front-end power supply, widely adopted in server and tele-communication systems is shown in Figure 1. The AC input voltage is in range of 85V~240V, while the output voltage 48V is keep constant with high accuracy and low ripple level. The intermediate bus voltage (IBV) in range of 385V is generated to ensure enough headroom for the PFC boost con-verter in order to ensure low THD-level for wide input voltage range. PFC converters used in server and telecommunication-applications are designed to operate in con-tinuous conduction mode (CCM). When the converter is operating in light load condition, it will oper-ate in DCM condition and the

Figure 1: PFC and DC/DC front-end power supply for distributed power architecture in server and telecommunication applications

POWER SUPPLIES


3332

POWER SUPPLIES



in range from 5% up to 30% of nominal output power is valid: the lower output voltage, the higher the converter efficiency. This is because switching loses become dominant for low output current. For higher output power level, the efficiency becomes higher when Uout increases. This is because conductor losses become domi-nant by high output current level.

So, for some particular power level intervals, monotone function efficiency versus output voltage can be assumed. Power efficiency improvement can be achieved by changing output voltage when output power changes. The digital power controllers ADP1047/48 allow easy implementation of a linear function UOUT for varies output power level. Figure 3 shows an example of the linear output voltage change versus output power. The so-called “Smart Volt-age” function can be programed by means of guided user interface.

Power losses analysis for DC/DC convertersDC/DC converter efficiency behav-ior was analyzed for different input voltage level in order to find the optimum system efficiency. One dual phase interleaved 300W con-verter with Uin range 350V~400V and with Uout=12V has been analyzed [7]. This DC/DC using digital power controller ADP1046 was equipped with dynamic phase shedding, which allows phase dis-abling at low output power range. The power efficiency behavior versus output power for different

Uin values was measured.

The converter works at light load with higher efficiency, when Uin is lower than nominal value. At high output power, the efficiency increases as Uin increases. This behavior is similar to the efficiency behavior of PFC converter from subchapter 3.1. Figure 4 demon-strates power efficiency behavior of DC/DC converter. Some efficiency gain at weak load can be achieved by using phase shedding mode. One phase was disabled at output power range below 100W. It can be seen additional efficiency gain below 100W output power.

Dynamic control of intermediate bus voltage Earlier the power efficiency behav-ior of PFC and of DC/DC convert-ers for different UIBV has been analyzed. In general, power ef-ficiencies of both converters be-come higher at low output power range when the UIBV becomes lower. The power efficiencies become higher at nominal out-put power range when the UIBV becomes higher. This means, it exists an optimum UIBV offering the maximum system efficiency for particular output load. Thus, dynamically control of UIBV ver-

Figure 3: New adaptive bus voltage mode allows linear voltage change in respect to two output power levels P1 and P2

Figure 4: Power efficiency of DC/DC converter for two different input voltage 350V and 395V

voltage conversion ratio becomes nonlinear as a function of induc-tor current and input and output voltages, this result increased line current distortion [5].

The inductor peak current will be higher when operating in DCM and results higher switching losses with fixed switching frequency con-trol scheme. One method of reduc-tion the switching power losses during light load is decreasing output voltage. Fig.1 shows state of the art front-end power sup-ply using one phase digital con-trolled PFC and digital controlled full bridge forward converter. The PFC controller needs UIBV signal for regulation and IAC signal for protection and telemetry. Similarly, the DC/DC controller uses signals UOUT for regulation and IOUT for protection/telemetry.

Optionally, both controllers could communicate with a master sys-tem by serial control bus. This maser unit can control both con-verters in order to find out the

maximum system efficiency for particular output load by means of sweep method, in which the output voltage will be changed in order to find out minimum out-put power consumption [6]. The UOUT needs to be regulated in a range, which is specified by the load. After the sweep procedure is finished, the master controller adjusts the optimum UOUT. This sweep procedure ensures maxi-mum system efficiency by dynami-cal optimization of output voltage.

A similar method could be adopt-ed for PFC- and DC/DC-converter system: UIBV can be changed in order to minimize power con-sumption of the down-streamed DC/DC converter, which builds the load of the PFC stage.

Dynamic control of intermediate voltage in PFC+DC/DC systemAs the digital PFC- and DC/DC controllers need to measure con-verters system-values like input/output voltages and input/output currents (ref. to Figure 1), so there

is possible to avoid the external sweep function provided by master controller [6] to keep the system PFC+DC/DC in optimum system efficiency point. This is possible by knowledge the efficiency behaviors of:• PFC converter for the different

output load and for different output voltage

• DC/DC converter for differ-ent input voltage and differ-ent output load, when UOUT =const

As the PFC output voltage repre-sents DC/DC input voltage, so the proprietary dynamically adjust-ment of the intermediate voltage UIBV allows the system to work in optimum power efficiency. Thus, PFC- and DC/DC-converter can work autarky and independently from each other. The efficiency analysis of PFC- and DC/DC-converter for common UIBV are needed to find the optimum sys-tem efficiency. Power losses analysis for PFC boost converterThe efficiency behavior of a PFC-boost converter was performed on one 300W system utilizing digital controller ADP1047 [8]. By keeping constant input voltage 230Vrms and constant output voltage UOUT in steps 350V, 365V, 380V, 395V, the power efficiency for different output power level was measured. The results are presented in Figure 2.

The power efficiency is a function of output voltage, as seen in the Figure 2. For the output power

Figure 2: Efficiency of 300W PFC boost converter [8] for different output power and output voltage levels

34

POWER SUPPLIES


sus output power can be applied to increase system efficiency. One method providing dynamically control UIBV can be realized by remote control by means of serial control bus, as suggested in Fig.1. One master controller and galvan-ic isolation between PFC- and DC/DC serial bus nodes are needed.

To overcome those disadvantages and to simplify the control law of optimum system efficiency one new algorithms can be used. The input power level value can be taken for dynamically control of UIBV instead of output power level. Some digital power control-lers have the ability to measure input power level, as this function is requested for telemetry and for protection measures.

The digital power controller ADP1047 is equipped with dedi-cated circuit allowing accurate measurement input power and with a control circuit allowing dynamically adoption of UIBV.

It is simple to program the gain and power thresholds for the dynamically UIBV control. Figure 3 presents how to adjust the power thresholds and output voltage level in guided user interface (GUI) of ADP1047. This setup shows lin-ear function UIBV for input power level between 65W and 175W.

Those power thresholds were adjusted as result of power ef-ficiencies analysis PFC-and DC/DC-converter. Above input power value 65W, UIBV increases linear allowing the system to work by optimum power efficiency. Above power level 175W, UIBV remains at 395V providing higher efficiency at high UIBV and high output power level. The system efficiency plot for two constant values UIBV and one dynamically controlled UIBV is presented in Figure 5. The red line represents system efficiency for constant UIBV =350V, where the green line for UIBV =395V. The blue line represents the sys-

tem efficiency, when dynamically control UIBV (SMART-Voltage mode) is enabled for system pa-rameters presented in Fig.3. The sense of SMART-Voltage mode is to adjust the power thresholds at the points allowing achieving the upper efficiency-envelope lines in Fig.2 and Figure 4 for minimum and for maximum UIBV values. The minimum- and maximum UIBV values are determinate by the PFC- and by DC/DC dimension-ing. The efficiency cross-points for minimum and maximum of output voltages (PFC) as well as of input voltage (DC/DC) determine the power thresholds of the SMART-mode function.

An adaptable processA new method offering dynami-cally adjusting of intermediate bus voltage in power supply system consisting of PFC- and DC/DC converter has been presented. The method can be adapted for autono-mous efficiency optimization. The PFC controller adjusts the output voltage for wide input power range in order to achieve the best efficien-cy for particular output load value. The dynamically adjusting takes into account the efficiency behavior of PFC- and of DC/DC stage. The results show efficiency improve-ment in range of 2…3 % for whole output power range. The SMART-function, implemented into digital PFC controller allows self-tuned, adaptive change of the intermediate voltage for optimum system power efficiency in wide load range.

www.analog.com

Figure 5: System power efficiency comparison for constant IBV of 350V (red trace), of 395V (green trace) and for dynamically adopted IBV by means of SMART-algorithms (blue trace)

Special Report:Health Medical & Mobility

Inside:

Dell Children’s Medical Center saves power with LED lighting...

Proper ESD protection is key to ensuring reliability of

medical wearables...

Compact regulator speeds digital endoscopy adoption...

34

37

40

3736 WWW.POWERSYSTEMSDESIGN.COM WWW.POWERSYSTEMSDESIGN.COM

SPECIAL REPORT : HEALTH MEDICAL & MOBILITY POWER SYSTEMS DESIGN 2014OCTOBER

Dell Children’s Medical Center saves power with LED lighting

By: Karyn Gayle, Acuity Brands

Acuity Brands helps Central Texas hospital become first to achieve LEED for Healthcare Platinum Certification

Dell Children’s Medical Center of Central Texas, part of the Seton Healthcare

Family in Austin, began construction of a new addition to its 500,000 square-foot medical center in November 2011. The hospital had specific lighting and energy requirements for its new 85,000 square-foot, 72-bed patient tower and children’s hospital. It wanted to install an LED lighting system that would perform advanced controls functions seamlessly and with ease (see Figure 1).

“Because LED technology has progressed so much, we wanted to integrate it as much as we could into the new building,” said Phillip Risner, Senior Project Manager at Seton Healthcare Family.

The hospital’s mission was to create a “green” hospital and continue to build on the sustainability accomplishments it had already achieved with the original hospital construction. Another goal for the hospital was to achieve LEED for Healthcare

Platinum certification for the new patient tower.

“Healthcare buildings are so energy and water intensive, and under 24/7 operation, so becoming sustainable is a huge challenge,” said Risner. “But, we were up to it. Since health is holistically related to environmental issues as well as personal issues, it meant a great deal for us - and to our patients - to try to achieve LEED for Healthcare Platinum certification for sustainability purposes.”

The hospital had various requirements for its lighting controls strategy. Multiple dimming options were required to adjust the lighting for specific reasons such as reducing light in the hallways at night. Additionally, the team also wanted the ability to track the energy savings achieved from controlling the lighting.

The hospital enlisted the help of Polkinghorn Group Architects /

CCRD Partners engineers, Prism Electric and Beck, to identify lighting and controls solutions for its new patient tower.

“The hospital set a goal to achieve LEED for Healthcare Platinum certification, so there was a push for the organization to be environmentally friendly and to be good stewards of sustainability,” said Brian

Horras, Project Manager at Beck. “Because this is a new facility, and the client wanted the latest and most effective new technology, they advocated for better lighting and LED. Another bonus is from a maintenance cost standpoint; you don’t have to replace lighting as often with the LEDs.”

Affordable LED Lighting and ControlsWith the goal of installing more than 90 percent LED throughout the new tower, the hospital selected Lithonia Lighting VT Series LED fixtures and controls from Acuity Controls, which they calculated to be less expensive and more efficient than other options (See Figure 2). LED lighting and lighting control systems were installed throughout the entire building: patient rooms, corridors, nurses’ stations and office spaces.

“We actually chose a lighting control system based on the compatibility with the LED lighting fixtures we were

looking at,” said Horras. “We had it narrowed down to three manufacturers but the final decision was made by the performance specifications and the capability of the Acuity Brands lighting compared to other similar systems. These specific LED luminaires and controls compared to the original specified high performance fluorescent resulted in an initial cost reduction of $75,000.”

In order to achieve additional energy savings and maintenance costs, the hospital installed 2,878 nLight devices. Motion sensors are now being used in 95 percent of the building, and in the 72 new patient rooms. The controls are also being used to track energy use in the facility.

Seeing the GreenVT Series LED luminaires deliver the majority of the lighting and energy savings for the new wing. These fixtures illuminate hallways and common areas. In order to match the look and light levels of the current hospital,

these hallway fixtures are set to approximately 40 to 50 percent light output at all times. A time clock does not have the ability to manage all 72 rooms equipped with sensors. But, the VT Series LED luminaires in the hallways and corridors provide a simple solution because they feature digital lighting controls integrated directly into the fixture during the manufacturing process. The luminaires also integrate directly with a hospital nurse call system to illuminate differently during a code-blue incident (cardiac arrest, breathing difficulty, etc.). If anyone touches a code blue button, lights in the entire corridor turn on.

In addition to the VT Series LED fixtures with nLight controls, Dell Children’s Medical Center of Central Texas also installed the LED Step Light from Winona as a night-light in patient bathrooms, which features amber light. The benefit of amber light is patient sleep cycles are not disrupted, while the hospital offers enough illumination to help provide quality lighting to help patients from slipping and falling (see Figure 3).

The nLight-enabled luminaires installed throughout the new patient tower are helping to increase patient safety and reduce maintenance and energy costs. Between May 2013 and February 2014, Dell Children’s

Figure 1: Dell Children’s Medical Center of Central Texas needed an advanced solid-state lighting solution

Figure 2: Lithonia Lighting VT Series LED fixture and control from Acuity Control

38 WWW.POWERSYSTEMSDESIGN.COM

SPECIAL REPORT : HEALTH MEDICAL & MOBILITY

Medical Center of Central Texas reported a total savings of approximately 180,000 kilowatts per hour of energy from the use of nLight controls, including occupancy sensors, photocells, dimming and switching.

Dell Children’s Medical Center of Central Texas became the first hospital in the world to achieve LEED for Healthcare Platinum certification. In order to do this, the hospital had to comply with strict guidelines, and earn at least 80 out of the 100 points possible.

“It’s a high bar,” explained Brendan Owens, Vice President of LEED Technical Development US Green Building Council. “LEED platinum, which means a

Figure 3: LED Step Light from Winona is a night-light which features amber light

project team has achieved at least 80 percent of the available points, requires a project team to take a highly integrated approach to building design, construction and operations. Because of the importance of lighting from an whole building energy perspective, USGBC emphasizes lighting efficiency as a key strategy to optimize operational energy use.”

The hospital worked diligently to achieve LEED certification. “We have received great feedback because we have achieved LEED Platinum

for healthcare guidelines,” said Horras. “That is very difficult to achieve. This is one of the few projects to get LEED under the new guidelines, and one of two medical centers that have achieved ANY level of certification based on the new healthcare guidelines.”

Even after achieving LEED Platinum status, Dell Children’s Medical Center of Central Texas is still working to improve its energy reductions. The hospital continues to expect further energy savings from adjusting lighting and controls strategies moving forward. Lithonia Lighting® VT Series LED luminaires combine aesthetics with intelligent, high performance LED light

engines to create the ideal LED luminaire solution for healthcare environments. Long-life LEDs coupled with high-efficiency drivers provide superior quality illumination. Embedded nLight controls from Acuity Controls make each luminaire addressable, allowing it to digitally communicate with other nLight-enabled controls such as dimmers, switches, occupancy sensors and photocontrols.

Featured benefits include:• nLight controls system

provides design flexibility and ease of installation, while offering increased energy savings.

• Novel plug-and-play convenience as devices and luminaires automatically discover each other and self-commission.

• Novel grid interfacing allows fixture trim to hang level with architectural ceiling tiles.

• The luminaires are equipped with a unique lumen management system that actively manages the LED light source so that constant lumen output is maintained over system life.

• The expected life is more than 50,000 hours.

www.acuitybrands.com

Proper ESD protection is key to ensuring reliability of medical wearables

By: James Colby, Littelfuse

Smaller and smarter must also be safer

It is, by no means, hyperbolic to say that we are on the verge of another revolution. A revolution of the way we

leverage modern technologies to access information about our own health conditions. Until only recently, anyone interested in obtaining even the most basic information (blood glucose, heart rate, etc.) would have to visit a medical professional or use an invasive tool to get a drop of blood for use in a blood glucose meter. The costs, time, access/availability, and inconvenience have always made it very difficult to collect physiological data.

The “Quantified Self” movement promises to help us understand our health parameters at all times. Quantified Self is essentially a concept by which electronic sensors monitor a person’s physiological parameters to understand the current state of the body (heart rate, glucose, hydration, oxygen consumption, sleep patterns, calories ingested, etc.) in real time.

The main goal here is to enable people to act on their physiological information to improve their health, state of mind, etc. Unfortunately, we have always treated the human body as a “black box” that must be responded to rather than be understood in real time. But, a real-time understanding (acquired through physiological monitoring) would allow us to change behaviors to achieve a desired condition (lower blood pressure, weight loss, faster recovery from injury/surgery, etc.). Without this information on one’s current state, we would hardly be able to make plans and move to the next step.

If this information were readily

available, it would encourage people to work toward improving their overall health much faster. Even making simple changes like taking the stairs instead of the elevator or drinking water instead of consuming sugary soft drinks would have a measurable and recognizable impact and thus lead to better health in general.

The explosion in wearable techWearable technologies that incorporate physiological sensors

Figure 1: The next generation of wearable monitoring devices has already started transforming the way people capture and record physiological data



4140 WWW.POWERSYSTEMSDESIGN.COM WWW.POWERSYSTEMSDESIGN.COM

SPECIAL REPORT : HEALTH MEDICAL & MOBILITY POWER SYSTEMS DESIGN 2014OCTOBER

(often called “dynamic resistance”). By reducing the dynamic resistance, the ESD protector carries significantly more of the surge current than the circuit being protected. In doing so, it reduces the electrical stress on the integrated circuit and ensures that it survives. The SP3014 Series TVS Diode Array from Littelfuse, for example, has a dynamic resistance value of less than 0.1Ω to provide best-in-class performance.

• Lower capacitance to avoid interfering with high speed data transfer: Although circuit protection is vital to an ESD protection device’s purpose, it is important to keep in mind that it must perform this role without interfering with the day-

to-day functioning of the circuit it protects. For example, on an RF interface (Bluetooth, ZigBee, etc.) or wired port like USB 2.0, the ESD protector must be prevented from causing distortion or loss of strength of the data

signals. To ensure signal integrity, the capacitance of the ESD protector must be minimized without compromising protection levels. The SP3022 Series TVS Diode from Littelfuse features a capacitance value of 0.35pF, ensuring that it will remain “invisible” to high-speed signals.

• Smaller form factors to fit the limited board space available in the wearable devices: No matter how well a protection device performs, it won’t be particularly useful if it can’t fit into the application it’s meant to protect. Wearable medical devices will gradually get thinner and smaller (watches, wristbands, chest bands) or be incorporated directly into clothing, so that

Figure 3: SP1012 Series five-channel bidirectional TVS Diode Arrays provide reliable protection against highly destructive electrostatic discharges. Their bidirectional configuration provides symmetrical protection when AC signals are present

the circuit boards will have minimal space available for the ESD protection solutions. Discrete diodes are ideal for giving design engineers exceptional board layout flexibility; and SP1020 (30pF) and SP1021 (6pF) Series are packaged in the 01005 package outline to minimize the amount of space they take up. In addition, the SP1012 Series (see Figure 3) packs five bi-directional channels of protection in a compact 0.94mm x 0.61mm package outline for applications that demand reducing part counts and protection device footprint.

Although it is obvious that upcoming wearable technologies will help advance users’ quality of life, they will continue to pose challenges for the designers. Making sure that they also provide long-lasting reliability is therefore extremely important. In fact, they must allow for accurate measurements to be made no matter how active the lifestyle or how often they are subjected to potentially damaging ESD events. Manufacturers of ESD protection devices are equally committed to working as hard as wearable device designers to provide protection for these devices while not interfering with their core functionality.

www.littelfuse.com

are becoming increasingly available. Rather than forcing users to carry blood glucose meters with them, the next generation of monitoring devices will actually be worn on the body itself (similar to the device in Figure 1). This nearly transparent incorporation of these medical sensors will enable people to monitor their condition in near-real time and allow them to monitor considerably more data points over the course of a day. Initial examples of this novel approach such as wristbands that are capable of measuring how far a person has walked, pulse, etc. are already on the market. Unobtrusive undergarments (undershirts, bras, etc.) designed for use during fitness training allow for data to be collected on key parameters such as pulse, breathing rate, posture, and even distance travelled.

But as beneficial as these monitoring options are, the biggest breakthroughs are yet to come (Figure 2). Just imagine for a moment if people with diabetes no longer had to prick their fingers several times a day to measure their blood glucose in order to adjust their insulin dose. This would not only make it much easier to collect this vital data more frequently but also eliminate the pain.. This in turn would help people with diabetes to actually control their blood glucose levels more effectively

over the long term and postpone or even prevent the most serious consequences of this increasingly common disease. Researchers in Germany have even developed a method that uses infrared laser light and a technique called photo-acoustic spectroscopy to determine blood glucose levels without having to penetrate through the skin. The advantage here is that this method is non-invasive and could one day revolutionize the diagnosis, monitoring, and treatment of diabetes.

Interestingly enough, the fact that these systems touch skin is not only their greatest strength, but also a potential weakness. After all, they will inevitably be exposed to user-generated static electricity, which can render them inoperable without the proper protection. After all, a simple human touch can be all it takes to initiate an electrostatic discharge (ESD) transient. The reason is that any of the sensor circuits, buttons, battery-charging interfaces, or data I/Os

could provide a path for ESD to enter the device.

Manufacturers of semiconductor-based ESD protection components are working hard to improve the capabilities of these solutions. Littelfuse, Inc., for instance, continually invests in developing new processes that enhance their protection products.

Recent component innovations include:• Lower clamping voltage

to protect even the most sensitive circuits: During an ESD event, the main job of the ESD protector is to divert and dissipate as much of the ESD transient as possible. This characteristic is improved by reducing the on-state resistance

Figure 2: Wristbands will soon be able to communicate important information on blood sugar levels, blood pressure, cholesterol, heart rate, nutrition, pulse oximetry, sleep, and other relevant health matters to a user’s smartphone for easy transfer to a doctor

4342




Compact regulator speeds digital endoscopy adoption

By: Afshin Odabaee, Linear Technology

Current endoscopy trends are pushing adoption of digital imaging tech

Since the beginning of time medical doctors have looked for better ways to diagnose and

treat patients who suffer from in-ternal ailments or injury. The abil-ity to examine and treat patients from within in a minimally invasive way and with the least amount of discomfort has been an important part of medical practice starting in the 1800s. Current endoscopy trends are pushing towards adop-tion of digital imaging techniques leading to great advances in image resolution, tissue identification, and explaining the treatment to the patient and their families.

These features require multiple digital processors to process and distribute the image data. There arises the design challenge - how to fit all the electronics and associ-ated power regulators in the same form factor as the previously in-stalled endoscopic camera control units (CCUs) to minimize installa-tion and adoption costs.

History of EndoscopyMost historians consider Bozzini’s Lichleiter to be the first resem-blance of the endoscope we know today. Invented in the early 1800s,

it was rigid with angled mirrors to project the image to the doctor’s eye, but with only a single candle for illumination image quality was poor. Then around the turn of the 20th century, illumination tech-niques had improved to the point where several inventors created a way to capture endoscopic still images on camera. In the 1950s, Japanese pioneers Mori and Ya-madori recorded the world’s first motion picture from an endoscope featuring a live birth. The disad-vantage with photography and mo-tion pictures of that time was that the images could not be shared or manipulated in real time. Now modern digital imaging technol-ogy supports these functions with better resolution than ever before as we continue along the path laid out by these early pioneers.

The Move towards Digital Endos-copy In the 21st century, CMOS image sensors have reached the image resolution and low power dissipa-tion sought by medical profession-als. These image sensors provide high quality images at resolutions up to full HD (1980 x 1080 pixels) and beyond. Some companies are taking a step beyond standard

2D HD images by introducing 3D stereoscopic endoscopes. Power dissipation (and resulting tem-perature rise) is also an important factor as the CMOS sensor is often situated in the camera head at end of the endoscope in a form fac-tor designed for convenient hand manipulation by the surgical team to position the lens to present the desired view. The image resolution and low power dissipation of mod-ern CMOS sensors are the founda-tion for the high interest around digital endoscopy.

Digital endoscopy benefits doc-tors and patients in several ways: 1) A digital image (or video) in real time enables doctors to col-laborate with their peers wherever they might be around the globe for more effective treatment and faster recovery; 2) The image can be instantaneously manipulated so different tissue structures can be more easily identified by the surgical staff; 3) The surgery can be easily recorded and annotated for training purposes; 4) 3D endo-scopes give surgeons even better visibility and depth perception to better target tissues for treatment; 5) The images are readily stored in the patient’s electronic medical

records for review by the patient and family for a more thorough explanation of the diagnosis, treat-ment and healing process. These five benefits do come with a re-quirement and enough processing horsepower to handle all the data.

Increasing digital processor con-tent decreases PCB Area It should be no surprise that these features: creating, displaying, ma-nipulating, distributing and storing the large amount of data created by these CMOS sensors requires a great amount of digital processing horsepower, most often located in the camera control unit (CCU). The main components of a typical endoscopic system include image processors, one or more FPGAs, memory, A/D converters, video display ports, and an Ethernet con-troller, which must be integrated to support these features. Subse-quently, a majority of these devices require multiple input voltages for operation. The resulting challenge to design engineers is how to sup-

port the dramatic increase in the number of power rails in a smaller space.

To facilitate integration of all these digital components and their ben-efits to patients and doctors alike, Linear introduced the space-saving LTM4644, a 14VIN quad-output step-down µModule regulator. In a 2.3cm x 1.5cm space (see Figure 1) on a dual-sided PCB, the LTM4644 regulates four output voltages

each delivering up to 4A of current to meet the power requirements of FPGA and other digital processors in digital endoscopy systems (see Figure 2). In contrast, comparable step-down module solution from competing vendors requires as much as four times more PCB area.

Moreover, with current sharable outputs, this step-down µModule regulator gives engineers the flex-ibility to configure the regulator as a single (16A), dual (12A, 4A or 8A, 8A), triple (8A, 4A, 4A) or quad (4A

each) output. This flexibility allows endoscope system engineers to source and qualify just one simple and compact µModule regulator for the variety of voltage and load current requirements of FPGAs, ASICs, microprocessors and other board circuitry.

The LTM4644 µModule regulator supports up to four unique out-put voltage rails from a 4V to 14V (or 2.375 to 14V with an external

Figure 1: The entire LTM4644 solution requires 3.5cm2 on a dual-sided PCB (one capacitor & four resistors on backside)

Figure 2: The LTM4644 Supports Up to Four Separate FPGA Power Rails

44



bias) input, delivering up to 4A per output to support the power needs of FPGAs, other digital processors, memory and supporting analog circuitry. Only six external ceramic capacitors (1206 case size) and four resistors (0603 or smaller case size) are required for a com-plete solution.

To save space and design time, the LTM4644 quad output regulator includes the DC/DC controllers, power switches, inductors and compensation in a 9 x 15 x 5.01mm BGA package. A 4V to 14V input supply (or 2.375V to 14V when an external bias supply is applied) powers each regulator channel de-livering a regulated output voltage adjustable between 0.6 to 5.5V with ±1.5% accuracy over line, load, and temperature. Separate input power pins allow engineers to power the four channels from different sup-ply rails if desired for power bud-geting regardless of whether the

outputs current share or not.

Taking another step to reduce solution area and cost, the four switch-ers within the LTM4644 oper-ate 90 degrees out of phase at a common frequency cut-ting the input capacitance in half for equiva-lent input ripple

performance. As a result, only six external ceramic capacitors (1206 case size), four feedback resistors (0603 case size or smaller) are required for a four-output configu-ration when operating from the same input supply (see Figure 2). The LTM4644’s small BGA pack-age combined with the very low external component requirement result in the smallest four-output 4A DC/DC step-down solution available today.

Controlled power-up sequencingThe LTM4644 has the features nec-essary to power loads that require specific power-up and power-down sequences. Each output has its own enable (RUN) logic pin, track (TRACK/SS) pin and power good (PGOOD) logic flag. The track pin allows engineers to control the output voltage slew rate dur-ing power-up and power-down by applying an analog input. The power good pin indicates when the

Figure 3: The LTM4644 provides a smooth monotonically rising output voltage to 5V nominal, even when the load is pre-biased (2.5V) for proper operation of FPGAs

output voltage is within ±10% of its target regulation point.

Because some voltage rails are powered before others possibly resulting in back-feed or when voltage is retained prior to start-up, some of the load’s power rails may be pre-biased at the instant the voltage regulator is enabled. Pre-biased outputs can pose a problem for some synchronous switching regulators whose control loops will immediately discharge the load to ground during start-up even though the FPGA requires a monotonically rising power source for proper operation. Beyond hav-ing the necessary control and in-dicator pins, LTM4644 provides a monotonically rising voltage even in the face of a pre-biased load (see Figure 3).

An even smaller solution for any missing power railsTo help engineers deal with last minute design changes, the LTM4624 is a single output version of the LTM4644 available in a tiny 6.25 x 6.25 x 5.01mm BGA package, the same height as the LTM4644. Requiring only two external ca-pacitors and one feedback resistor, the entire LTM4624 solution fits incredibly within one square centi-meter on a single-sided PCB (see Figure 4). The LTM4624 supports the same operating input, output voltage, and power-up sequencing features described in the previous Well Controlled Power-Up Se-quencing section.

The next level

Figure 4: Only two external ceramic capacitors (1206 case size) and one resistor (0603 case size or smaller) are required along side the LTM4624, forming a single 4A step-down regulator solution that fits within 1cm2 on a single-sided PCB or 0.5cm2 on a dual-sided PCB

The growing shift towards digital endoscopy prom-ises tremendous benefits for pa-tients and their doctors. CMOS image sensors cre-ate digital images and videos inside the body with the image resolution at sufficiently low operating tem-peratures suitable for handling by surgical teams to capture the de-sired field of view. These images and videos are easily

stored, enhanced and shared for a more effective, faster and lower cost treatment to the benefit of the patient, family and medical team. Accomplishing these three tasks requires a collection of digital processors, memory, A/D convert-ers, video display ports, and an Ethernet controller, which take up an increasing portion of the PCB area. As a result the point-of-load regulators must support an increasing number of voltage rails in a smaller space to maintain the endoscopic system’s form factor. The LTM4644 and LTM4624 step-down µModule regulators present a simple, compact solution de-signed to meet the challenge.

www.linear.com


Electric AutomationSystems and ComponentsInternational Exhibition and Conference Nuremberg, Germany, 25 – 27 November 2014

More information at+49 711 61946-828 or [email protected]

Answers for automationEurope's leading exhibition for electric automation offers you:• the comprehensive market overview• 1,600 exhibitors including all key players• products and solutions• innovations and trends

Your free entry ticket

www.mesago.com/sps/tickets

SPS_ANZ_2014_E_210x148_END.indd 1 30.06.14 11:48

46

PODCASThighl ights


By: Alix Paultre, Editorial Director, PSD

Paultre on Power -Multimedia highlights

Alfred Binder of ams on position sensors and intelligent motion (Podcast)

In this podcast Alfred Binder of ams talks to Alix Paultre of Power Systems Design about the importance of proper sensing in intelligent systems. Regardless of the horsepower of the processor, there is no precision without feedback. Sensors give a system the information it needs for proper and efficient operation …

Listen to Podcast | www.ams.com

AMS

Paul Lee of Intersil on energy management (Podcast)

In this podcast Paul Lee, Product Marketing Manger at Intersil, talks to Alix Paultre of Power Systems Design about energy magagement in advanced systems. In order to manage energy properly one must be able to measure it accurately. Intersil's ISL2802x digital power monitor (DPM) family delivers high accuracy …

Listen to Podcast | www.Intersil.com

Intersil

Saj Sahal & Suman Narayan of Fairchild on repositioning to address an evolving market (Podcast)

In this podcast Saj Sahal & Suman Narayan of Fairchild speak wth Alix Paultre of Power Systems Design about the embedded systems marketplace, where it's going, and industry trends as well as the recent changes at Fairchild made to address them. Among the topics discussed, they talk about their relaunched …

Listen to Podcast | www.fairchildsemi.com

Fairchild

Recent audio and video episodes from the “Paultre on Power” podcast series

www.Intersil.com

http://www.powersystemsdesign.com/paultre-on-power-alfred-binder-of-ams-on-position-sensors-and-intelligent-motion-podcast

www.ams.com

http://www.powersystemsdesign.com/paultre-on-power-saj-sahal-suman-narayan-of-fairchild-on-repositioning-to-address-an-evolving-market-podcast

www.fairchildsemi.com

http://www.powersystemsdesign.com/paultre-on-power-paul-lee-of-intersil-on-energy-management-podcast

Your Gateway to …the South American Power Electronics Market.

International Conference and Exhibitionfor Power Electronics, Intelligent Motion,Renewable Energy and Energy ManagementSão Paulo, 14 – 15 October 2014

More information at: +49 711 61946-0or pcim-southamerica.com

Power On!

David Niewolny of Freescale on designing for medical in the Cloud (Podcast)

In this podcast David Niewolny of Freescale talks to Alix Paultre of Power Systems Design about designing devices for the next generation of medical applications, from wearables to stationary cloud-based systems. From connectivity issues to battery life to system efficiency, device designers have a lot …

Listen to Podcast | www.freescale.com

Freescale

To listen to more Podcast

To Watch more Videos


Babu Chalamala of the IEEE on emerging energy technologies (Podcast)

In this podcast Babu Chalamala, IEEE Fellow, talks to Alix Paultre about the recent IEEE proceedings on next-generation energy and energy storage. Their work took a deep dive into emerging technologies in renewable energy, battery systems, microgrids, and more. In the discussion Babu and Alix cover issues such …

Listen to Podcast | www.ieee.org

IEEE

David Andeen of Maxim on industrial automation (Podcast)

In this podcast friend of the show David Andeen of Maxim Integrated talks to Alix Paultre of Power Systems Design about industrial control, industrial automation, motor control, and process automation applications. Due to the complexity of the systems involved, binary/digital sensors and switches are also frequently …

Listen to Podcast | www.maximintegrated.com

Maxim Integrated

http://www.powersystemsdesign.com/paultre-on-power-david-niewolny-of-freescale-on-designing-for-medical-in-the-cloud-podcast

www.freescale.com

http://www.powersystemsdesign.com/paultre-on-power-babu-chalamala-of-the-ieee-on-emerging-energy-technologies-podcast

www.ieee.org

http://www.powersystemsdesign.com/paultre-on-power-david-andeen-of-maxim-on-industrial-automation-podcast

www.maximintegrated.com

http://www.powersystemsdesign.com/podcasts

http://www.powersystemsdesign.com/videos

50

GREENpage


POWER SYSTEMS DESIGN

By: Alix Paultre, Editorial Director, PSD

The new Luddites

The current atmosphere of

development in the United

States is one of odd imbal-

ances and initiatives, a

place where advanced technologies

are being embraced or rejected in a

piecemeal fashion based more on

ideologies and politics than needs and

capabilities. This sad state of affairs

has placed the USA in a very danger-

ous situation in developing world tech-

nology markets.

One easy example of the dichotomy

of opinion on technology is Google

Glass. The same people who live with

a cell phone pressed into their hands

while staring up at public surveillance

cameras are also somehow intimi-

dated by a device that is no different

in basic functionality beyond the face-

oriented form factor.

I have a pair of Glass I use for blog-

ging at events, and have had several

altercations with “anti-Glassers”, one

surprising argument occurred recently

with a fellow tech editor (talk about

cognitive dissonance). In this case

privacy uncertainty (a joke today where

everyone has a camera in their hand

and on every building) and a feeling

that they are on a non-level tech play-

ing field seem to be the driving forces,

as nobody I talked to could properly

express exactly why they hated my

wearing them (all of these discussions

happened in public places).

Mostly, however, the pushback on

technology development is not due

to fear of tech (true Luddism) but a

clinging to legacy markets and tech-

nologies purely for profit’s sake. This

type of neo-Luddism is behind almost

every single market swing and disrup-

tion in history. This legacy pressure

is not new, extending back to the first

disruptive automation technology that

prompted Ned Ludd and his fellow

Englishmen (& women) to protest.

Ironically big business is the primary

motivator of tech resistance today.

Solar and alternate energy creates the

battlefield for these neo-Luddites, as

the oil & gas industry has no desire

to give up any of their market. They

cling to their legacy tech and lobby

government to put ridiculous counter-

productive legislation in place that

effectively stifles US development and

deployment of advanced alternate-

energy solutions. In their desire for

short-term gain they fail to see the

market collapse and destabilization

they are leading the country into.

The rest of the world isn’t taking

America’s lead in not developing alter-

nate energy, unsurprisingly. They see

that alternate energy is not only better

for the environment, renewable, and

technologically advanced, it is also a

liberation from the political pressures

of energy-producing countries that

may not have a complementary world

agenda. The sad result of this unequal

development effort will almost cer-

tainly be America’s taking a back seat

in the international alternate-energy

industry and falling even further into

backwater status as a market for these

advanced technologies.

This is not to say that I am against oil,

coal, and gas, those and their related

energy technologies will be around in

this world long after I am not. But we

can stop using fossil fuels in applica-

tions that we can serve with other

energy technologies.

www.powersystemsdesign.com

Ridley Engineering, Inc. 3547 53rd Ave W, Ste 347 Bradenton, FL 34210 US +1 941 538 6325

Ridley Engineering Europe Chemin de la Poterne Monpazier 24540 FR +33 (0)5 53 27 87 20 www.ridleyenginering.com

Designed for switching power supplies,it is simply the best product on the market for all of your frequency response measurement needs.

Quad 4A µModule Regulator

Info

Simplify your power. The LTM®4644 is a µModule® switchmode step-down regulator with 4 outputs, configurable as a single, dual, triple or quad. With this flexibility, a simple and compact 9mm x 15mm BGA µModule regulator can power the variety of voltage and load requirements of FPGAs, ASICs and microprocessors.

▼ Obtain Data Sheet▼ Request Demo Board▼ Download LTspice® Demo Circuits▼ Download CAD Symbols and Footprints▼ Supported by LTpowerCAD™ II

www.linear.com/product/LTM4644

1-800-4-LINEAR

Features

Current Share from 1 to 4 Outputs, up to 16A from 4VIN – 14VIN

, LT, LTC, LTM, Linear Technology, the Linear logo, LTspice and µModule are registered trademarks and LTpowerCAD is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.

Only 8 Capacitors and 4 Resistors

• 4V≤VIN≤14V or 2.375V≤VIN≤14V with External Bias Voltage

• 0.6V≤VOUT≤5.5V Each Output

• Guaranteed ±1.5% DC Output Voltage Accuracy from -40ºC to 125ºC

• Independent Input Supply Pins for Each Channel

• Output Overvoltage, Over Temperature and Short-Circuit Protection

• Internal Temperature Sensing Diode

8A4A4A4A4A

4A4A

8A

8A 4A

12A 16A

Quad Output Triple Output Dual Output Single Output

LTM4644 LTM4644 LTM4644 LTM4644 LTM4644

9mm x 15mm x 5.01mm(Actual Size)

Double-Sided PCB

LTM4644 Ad PSDNA.indd 1 3/4/14 1:40 PM

october 2014 - power systems design · extending battery life in wireless medical devices (pg 12 )...

Documents