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1996 Burr-Brown Corporation PDS-1293A Printed in U.S.A. May, 1996

VIN

Shield 1 Ext Osc +V S1 +VS2

GND1 V S1 VS2 GND2

23 20 3 13 12

5 21 4 15

Shield 2

VOUT

Com2

14

11

10

RG

RG

VIN+

1

22

2

24

Com1

Precision, IsolatedINSTRUMENTATION AMPLIFIER

DESCRIPTIONISO175 is a precision isolated instrumentation ampli-fier incorporating a novel duty cycle modulation-

demodulation technique and excellent accuracy. Asingle external resistor sets the gain. Internal inputprotection can withstand up to 40V without damage.The signal is transmitted digitally across a differentialcapacitive barrier. With digital modulation the barriercharacteristics do not affect signal integrity. This re-sults in excellent reliability and good high frequencytransient immunity across the barrier. Both the ampli-fier and barrier capacitors are housed in a plastic DIP.

ISO175 is easy to use. A power supply range of 4.5Vto 18V makes this amplifier ideal for a wide range of applications.

FEATURESRATED1500Vrms Continuous

2500Vrms for One Minute100% TESTED FOR PARTIAL DISCHARGEHIGH IMR: 115dB at 50HzLOW NONLINEARITY: 0.01%LOW INPUT BIAS CURRENT: 10nA maxLOW INPUT OFFSET VOLTAGE: 101mV maxINPUTS PROTECTED TO 40VBIPOLAR OPERATION: V O = 10VSYNCHRONIZATION CAPABILITY24-PIN PLASTIC DIP: 0.3" Wide

APPLICATIONSINDUSTRIAL PROCESS CONTROLTransducer Isolator, ThermocoupleIsolator, RTD Isolator, Pressure BridgeIsolator, Flow Meter IsolatorPOWER MONITORINGMEDICAL INSTRUMENTATIONANALYTICAL MEASUREMENTSBIOMEDICAL MEASUREMENTSDATA ACQUISITIONTEST EQUIPMENT

POWER MONITORINGGROUND LOOP ELIMINATION

International Airport Industrial Park Mailing Address: PO Box 11400, Tucson, AZ 85734 Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 Tel: (520) 746-1111 Twx: 910-952-11Internet: http://www.burr-brown.com/ FAXL ine: (800) 548-6133 (US/Canada Only) Cable: BBRCORP Telex: 066-6491 FAX: (520) 889-1510 Im mediate Product Info: (800) 548-61

ISO175I S O 1 7 5

SBOS050

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2

ISO175

1 + 50k

R G

0.125 + 101G

1 + 520

G

SPECIFICATIONSAt TA = +25 C, VS1 = VS2 = 15V, and R L = 2k unless otherwise noted.

ISO175P

PARAMETER CONDITIONS MIN TYP MAX UNITS

ISOLATION (1)

Voltage Rated Continuous:AC TMIN to T MAX 1500 Vrms

DC T MIN to T MAX 2121 VDC100% Test (AC, 50Hz) 1s; Partial Discharge 5pC 2500 VrmsIsolation-Mode Rejection

AC 50Hz 1500Vrms 115 dBDC 160 dB

Barrier Impedance 10 14 || 6 || pFLeakage Current VISO = 240Vrms, 50Hz 0.8 1 Arms

GAINV/V

Gain Error G = 1 0.35 %G = 10 0.07 %

G = 100 0.95 %Gain vs Temperature G = 1 11 ppm/ CNonlinearity G = 1 0.102 %

G = 10 0.04 %G = 100 0.104 %

INPUT OFFSET VOLTAGEInitial Offset G = 1, 100 mV

vs Temperature V/ C

vs Supply G = 1 2 mV/V

INPUTVoltage Range 10 VBias Current 10 nA

vs Temperature 40 pA/ COffset Current 10 nA

vs Temperature 40 pA/ C

OUTPUTVoltage Range 10 VCurrent Drive 5 mACapacitive Load Drive 0.1 FRipple Voltage 10 mVp-p

FREQUENCY RESPONSESmall Signal Bandwidth G = 1 60 kHz

G = 10 60 kHzG = 100 50 kHz

Slew Rate V O = 10V, G = 10 0.9 V/ s

POWER SUPPLIESRated Voltage 15 VVoltage Range 4.5 18 VQuiescent Current

VS1 7.4 mAVS2 7.5 mA

TEMPERATURE RANGEOperating 40 85 CStorage 40 125 C

NOTE: (1) All devices receive a 1s test. Failure criterion is 5 pulses of 5pc.

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ISO175

VS1

VS1+

Shield 1

Com 2

VOUT

GND 2

RG

EXT OSC

GND 1

VS2+

Shield 2

VS2

RG Com 1

VIN 1

2

3

4

5

10

11

12

24

23

22

21

20

15

14

13

VIN+

PIN CONFIGURATION

Any integrated circuit can be damaged by ESD. Burr-Brownrecommends that all integrated circuits be handled withappropriate precautions. Failure to observe proper handlingand installation procedures can cause damage.

ESD damage can range from subtle performance degrada-tion to complete device failure. Precision integrated circuits

may be more susceptible to damage because very smallparametric changes could cause the device not to meetpublished specifications.

ELECTROSTATICDISCHARGE SENSITIVITY

ABSOLUTE MAXIMUM RATINGS

Supply Voltage ................................................................................... 18VAnalog Input Voltage Range .............................................................. 40VExternal Oscillator Input ..................................................................... 25VCom 1 to GND1 ................................................................................... 1VCom 2 to GND2 ................................................................................... 1VContinuous Isolation Voltage: .................................................... 1500VrmsIMV, dv/dt ...................................................................................... 20kV/ sJunction Temperature ...................................................................... 150 CStorage Temperature ...................................................... 40 C to +125 CLead Temperature (soldering, 10s)................................................ +300 COutput Short Duration .......................................... Continuous to Common

The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumesno responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to changewithout notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrantany BURR-BROWN product for use in life support devices and/or systems.

PACKAGE/ORDERING INFORMATIONPACKAGEDRAWING

PRODUCT PACKAGE NUMBER (1) BANDWIDTH

ISO175P 24-Pin Plastic DIP 243-2 60kHz

NOTE: (1) For detailed drawing and dimension table, please see end of datasheet, or Appendix C of Burr-Brown IC Data Book.

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4

ISO175

100

Frequency (Hz)

10

1k

100

P e a

k I s o

l a t i o n

V o

l t a g e

ISOLATION MODE VOLTAGEvs FREQUENCY

10k 1M 100M1k 100k 10M

2kMax ACRating

DegradedPerformance

Max DC Rating

TypicalPerformance

TYPICAL PERFORMANCE CURVESAt TA = +25 C, VS1 = VS2 = 15V, and R L = 2k , unless otherwise noted.

1

Frequency (Hz)

0

60

40

20 P S R R ( d B )

PSRR vs FREQUENCY

100 10k 1M10 1k 100k

VS1 , VS2

+VS1 , +VS2

54

1

Frequency (Hz)

40

160

140

120

100

80

60

I M R ( d B )

100 10k 1M10 1k 100k

IMR vs FREQUENCY

0fIN (Hz)

0

20

40

V O U

T / V

I N ( d B )

SIGNAL RESPONSE vs CARRIER FREQUENCY

fC 2fC 3fC

0 0 0 0fc /2 fC /2 fC /2fOUT (Hz)

20dB/dec (for comparison only)

0

Time (s)

15

10

5

0

5

10

15

O u

t p u t V o

l t a g e

( V )

400 1000200 600 800

SINE RESPONSE ISO175(f = 2kHz, Gain = 10)

1

Frequency (Hz)

0.1A

100mA

10mA

1mA

100A

10A

1A L e a

k a g e

C u r r e n

t ( r m s

)

ISOLATION LEAKAGE CURRENTvs FREQUENCY

100 10k 1M10 1k 100k

240 Vrms

1500 Vrms

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ISO175

GAIN vs FREQUENCY80

60

40

20

0

20

G a

i n ( d B )

Frequency (Hz)

1k 10k 100k

G = 100

G = 10

G = 1

G = 1000

0

Time (s)

10

5

0

5

10

15 O u

t p u

t V o

l t a g e

( V )

15

10

5

0

5

10 I n p u

t V o

l t a g e

( V )

40 10020 60 80

STEP RESPONSE

0

Time (s)

10

5

0

5

10

15 O u

t p u

t V o

l t a g e

( V )

15

10

50

5

10 I n p u

t V o

l t a g e

( V )

200 500100 300 400

STEP RESPONSE

0

Time (s)

15

10

5

0

5

10

15

O u

t p u

t V o

l t a g e

( V )

400 1000200 600 800

SINE RESPONSE(f = 20kHz, Gain = 10)

TYPICAL PERFORMANCE CURVES (CONT)At TA = +25 C, VS1 = VS2 = 15V, and R L = 2k , unless otherwise noted.

INPUT COMMON-MODE RANGEvs OUTPUT VOLTAGE

Output Voltage (V)

C o m m o n - M o

d e

V o

l t a g e

( V )

15 10 0 5 15 5

15

10

5

0

5

10

1510

AllGains

AllGains

G = 1 G = 1

G 10 G 10

VD/2

+

+

VCM

VO

VD/2

INPUT BIAS AND OFFSET CURRENTvs TEMPERATURE

5

4

3

2

1

0

1 2

3

4

5 75 50 25 0 25 50 75 100 125

Temperature (C)

I n p u

t B i a s a n

d O f f s e

t C u r r e n

t ( n A )

IOS

Ib

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ISO175

Shield 1 Ext Osc +V S1 +VS2

GND 1 VS1 VS2

VS2

VOUT

+VS2

VS1

+VS1

VIN

VIN+RLOAD

GND 2

23 20 3 13 12

5 21

0.1F 1F+

4 15

Shield 2

VOUT

Com2

14

11

10

RG

1

22

2

24

Com 1

1F+

0.1F

1F 0.1F+

0.1F+

1F

128

102050

100

200500100020006000

10000

NOTE: (1) No Connection.

NC (1)

50.00k12.50k5.556k2.632k1.02k505.1

251.2100.250.0525.0110.005.001

NC (1)

49.9k12.4k5.62k2.61k1.02k511

24910049.924.910

4.99

DESIREDGAIN

RG()

NEAREST 1% R G()

BASIC OPERATIONISO175 instrumentation input isolation amplifier comprisesof a precision instrumentation amplifier followed by anisolation amplifier. The input and output isolation sectionsare galvanically isolated and EMI shielded by matchedcapacitors.

Signal and Power ConnectionsFigure 1 shows power and signal connections. Each powersupply pin should be bypassed with a 1 F tantalum capaci-tor located as close to the amplifier as possible. All groundconnections should be run independently to a common pointif possible. Signal Common on both input and output sec-tions provide a high-impedance point for sensing signalground in noisy applications. Com 1 and Com 2 must havea path to ground for bias current return and should bemaintained within 1V of GND1 and GND2, respectively.

SETTING THE GAINGain of the ISO175 is set by connecting a single external

resistor R G, connected between pins 2 and 22.

FIGURE 1. Basic Connections.

Commonly used gains and resistor values are shown inFigure 1.

The 50k term in equation (1) comes from the sum of thetwo internal feedback resistors. These on-chip metal filmresistors are laser trimmed to accurate absolute values. Theaccuracy and temperature coefficient of this resistor areincluded in the gain accuracy and drift specifications of theISO175.

The stability and temperature drift of the external gainsetting resistor R G, also affects gain. R Gs contribution togain accuracy and drift can be directly inferred from the

G =1 + 50 k

R G(1)

gain equation (1). Low resistor values required for highgain can make wiring resistance important. Sockets add tothe wiring resistance which will contribute additional gainerror (possibly an unstable gain error) in gains of approxi-mately 100 or greater.

INPUT COMMON-MODE RANGEThe linear voltage range of the input circuitry of the ISO175is from approximately 2.5V below the positive supply volt-age to 2.5V above the negative supply. As a differentialinput voltage causes the output voltage to increase, however,the linear input range will be limited by the output voltageswing of the internal amplifiers. Thus, the linear common-mode input range is related to the output voltage of thecomplete input amplifier.

This behavior also depends on the supply voltageseeperformance curves Input Common-Mode Range vs Out-put Voltage.

Input-overload can produce an output voltage that appearsnormal. For example, if an input overload condition drivesboth input amplifiers to their positive output swing limit, thedifference voltage measured by the output amplifier will benear zero. The output of the ISO175 will be near 0V eventhough both inputs are overloaded.

INPUT PROTECTIONThe input of the ISO175 is individually protected for volt-ages up to 40V referenced to GND1. For example, acondition of 40V on one input and +40V on the other inputwill not cause damage. Internal circuitry on each inputprovides low series impedance under normal signal condi-

tions. To provide equivalent protection, series input resistorswould contribute excessive noise. If the input is overloaded,

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ISO175

C1

Ext Osc onISO175(Pin 21)

C2

10k

6

5

82

3

TTLfIN

2.5k 200

+15V+5V

fIN140E-6( )C1 = 350pF

C2 = 10 X C 1, with a minimum 10nF

2.5k

6N136

10k

CX

OPA602

RX1F

Sq Wave InTriangle OutISO175Ext Osc

1k

the protection circuitry limits the input current to a safevalue of approximately 1.5 to 5mA. The inputs are protectedeven if the power supplies are disconnected or turned off.

SYNCHRONIZED OPERATIONISO175 can be synchronized to an external signal source.This capability is useful in eliminating troublesome beatfrequencies in multichannel systems and in rejecting ACsignals and their harmonics. To use this feature, an externalsignal must be applied to the Ext Osc pin. ISO175 can besynchronized over the 400kHz to 700kHz range.

The ideal external clock signal for the ISO175 is a 4V sinewave or 4V, 50% duty-cycle triangle wave. The Ext Oscpin of the ISO175 can be driven directly with a 3V to 5Vsine or 25% to 75% duty-cycle triangle wave and the ISOamps internal modulator/demodulator circuitry will syn-chronize to the signal.

ISO175 can also be synchronized to a 400kHz to 700kHzSquare-Wave External Clock since an internal clamp andfilter provide signal conditioning. A square-wave signal of

25% to 75% duty cycle, and 3V to 20V level can be usedto directly drive the ISO175.

With the addition of the signal conditioning circuit shown inFigure 2, any 10% to 90% duty-cycle square-wave signalcan be used to drive the ISO175 Ext Osc pin. With the valuesshown, the circuit can be driven by a 4Vp-p TTL signal. Fora higher or lower voltage input, increase or decrease the 1k resistor, R X, proportionally, e.g. for a 4V square-wave(8Vp-p) R X should be increased to 2k . The value of C Xused in the Figure 2 circuit depends on the frequency of theexternal clock signal. C X should be 30pF for ISO175.

generates an output signal component that varies in bothamplitude and frequency, as shown by the lower curve. Thelower horizontal scale shows the periodic variation in thefrequency of the output component. Note that at the carrierfrequency and its harmonics, both the frequency and ampli-tude of the response go to zero. These characteristics can beexploited in certain applications.

It should be noted that for the ISO175, the carrier frequency

is nominally 500kHz and the 3dB point of the amplifier is60kHz. Spurious signals at the output are not significantunder these circumstances unless the input signal containssignificant components above 250kHz.

When periodic noise from external sources such as systemclocks and DC/DC converters are a problem, ISO175 canbe used to reject this noise. The amplifier can be synchro-nized to an external frequency source, f EXT , placing theamplifier response curve at one of the frequency andamplitude nulls indicated in the Signal Response vs Car-rier Frequency performance curve. Figure 3 shows cir-cuitry with opto-isolation suitable for driving the Ext Oscinput from TTL levels.

ISOLATION MODE VOLTAGEIsolation Mode Voltage (IMV) is the voltage appearingbetween isolated grounds GND1 and GND2. The IMV caninduce errors at the output as indicated by the plots of IMVversus Frequency. It should be noted that if the IMV fre-quency exceeds f C /2, the output will display spurious out-puts in a manner similar to that described above, and theamplifier response will be identical to that shown in theSignal Response vs Carrier Frequency performance curve.This occurs because IMV-induced errors behave like input-referred error signals. To predict the total IMR, divide theisolation voltage by the IMR shown in IMR vs Frequencyperformance curve and compute the amplifier response tothis input-referred error signal from the data given in theSignal Response vs Carrier Frequency performance curve.

FIGURE 2. Square-Wave to Triangle Wave Signal Condi-tioner for Driving ISO175 Ext Osc Pin.

CARRIER FREQUENCY CONSIDERATIONSISO175 amplifier transmit the signal across the ISO-barrierby a duty-cycle modulation technique. This system workslike any linear amplifier for input signals having frequenciesbelow one half the carrier frequency, f C. For signal frequen-cies above f C /2, the behavior becomes more complex. TheSignal Response vs Carrier Frequency performance curvedescribes this behavior graphically. The upper curve illus-trates the response for input signals varying from DC tof C /2. At input frequencies at or above f C /2, the device

FIGURE 3. Synchronization with Isolated Drive Circuit forExt Osc Pin.

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ISO175

Due to effects of very high-frequency signals, typical IMVperformance can be achieved only when dV/dT of theisolation mode voltage falls below 1000V/ s. For conve-nience, this is plotted in the typical performance curvefor the ISO175 as a function of voltage and frequency forsinusoidal voltages. When dV/dT exceeds 1000V/ s butfalls below 20kV/ s, performance may be degraded. At ratesof change above 20kV/ s, the amplifier may be damaged,

but the barrier retains its full integrity. Lowering the powersupply voltages below 15V may decrease the dV/dT to500V/ s for typical performance, but the maximum dV/dTof 20kV/ s remains unchanged.

Leakage current is determined solely by the impedance of the barrier capacitance and is plotted in the Isolation Leak-age Current vs Frequency curve.

ISOLATION VOLTAGE RATINGSBecause a long-term test is impractical in a manufacturingsituation, the generally accepted practice is to perform aproduction test at a higher voltage for some shorter time.The relationship between actual test voltage and the continu-ous derated maximum specification is an important one.

Historically, Burr-Brown has chosen a deliberately conser-vative one: VTEST = (2 x ACrms continuous rating) +1000V for 10 seconds, followed by a test at rated ACrmsvoltage for one minute. This choice was appropriate forconditions where system transients are not well defined.

Recent improvements in high-voltage stress testing haveproduced a more meaningful test for determining maximumpermissible voltage ratings, and Burr-Brown has chosen toapply this new technology in the manufacture and testing of the ISO175.

PARTIAL DISCHARGEWhen an insulation defect such as a void occurs within aninsulation system, the defect will display localized corona orionization during exposure to high-voltage stress. This ion-ization requires a higher applied voltage to start thedischarge and lower voltage to maintain it or extinguish itonce started. The higher start voltage is known as theinception voltage, while the extinction voltage is that levelof voltage stress at which the discharge ceases. Just as thetotal insulation system has an inception voltage, so do theindividual voids. A voltage will build up across a void untilits inception voltage is reached, at which point the void willionize, effectively shorting itself out. This action redistrib-

utes electrical charge within the dielectric and is known aspartial discharge. If, as is the case with AC, the appliedvoltage gradient across the device continues to rise, anotherpartial discharge cycle begins. The importance of thisphenomenon is that, if the discharge does not occur, theinsulation system retains its integrity. If the discharge

begins, and is allowed to continue, the action of the ions andelectrons within the defect will eventually degrade anyorganic insulation system in which they occur. The measure-ment of partial discharge is still useful in rating the devicesand providing quality control of the manufacturing process.The inception voltage for these voids tends to be constant, sothat the measurement of total charge being redistributedwithin the dielectric is a very good indicator of the size of the

voids and their likelihood of becoming an incipient failure.The bulk inception voltage, on the other hand, varies withthe insulation system, and the number of ionization defectsand directly establishes the absolute maximum voltage (tran-sient) that can be applied across the test device beforedestructive partial discharge can begin. Measuring the bulk extinction voltage provides a lower, more conservative volt-age from which to derive a safe continuous rating. Inproduction, measuring at a level somewhat below the ex-pected inception voltage and then derating by a factorrelated to expectations about system transients is an ac-cepted practice.

PARTIAL DISCHARGE TESTINGNot only does this test method provide far more qualitativeinformation about stress-withstand levels than did previousstress tests, but it provides quantitative measurements fromwhich quality assurance and control measures can be based.Tests similar to this test have been used by some manufac-turers, such as those of high-voltage power distributionequipment, for some time, but they employed a simplemeasurement of RF noise to detect ionization. This methodwas not quantitative with regard to energy of the discharge,and was not sensitive enough for small components such asisolation amplifiers. Now, however, manufacturers of HVtest equipment have developed means to quantify partialdischarge. VDE in Germany, an acknowledged leader inhigh-voltage test standards, has developed a standard testmethod to apply this powerful technique. Use of partialdischarge testing is an improved method for measuring theintegrity of an isolation barrier.

To accommodate poorly-defined transients, the part undertest is exposed to voltage that is 1.6 times the continuous-rated voltage and must display less than or equal to 5pCpartial discharge level in a 100% production test.

APPLICATIONSThe ISO175 isolation amplifier is used in three categories of applications:

Accurate isolation of signals from high voltage groundpotentials,

Accurate isolation of signals from severe ground noise and,

Fault protection from high voltages in analog measure-ments.

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IMPORTANT NOTICE

Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinueany product or service without notice, and advise customers to obtain the latest version of relevant informationto verify, before placing orders, that information being relied on is current and complete. All products are soldsubject to the terms and conditions of sale supplied at the time of order acknowledgment, including thosepertaining to warranty, patent infringement, and limitation of liability.

TI warrants performance of its semiconductor products to the specifications applicable at the time of sale inaccordance with TIs standard warranty. Testing and other quality control techniques are utilized to the extentTI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarilyperformed, except those mandated by government requirements.

Customers are responsible for their applications using TI components.

In order to minimize risks associated with the customers applications, adequate design and operatingsafeguards must be provided by the customer to minimize inherent or procedural hazards.

TI assumes no liability for applications assistance or customer product design. TI does not warrant or representthat any license, either express or implied, is granted under any patent right, copyright, mask work right, or otherintellectual property right of TI covering or relating to any combination, machine, or process in which such

semiconductor products or services might be or are used. TIs publication of information regarding any thirdpartys products or services does not constitute TIs approval, warranty or endorsement thereof.

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