ti confidential – selective disclosure bms deep dive 2012 1 battery charger design (1s): key...

TI Confidential – Selective DisclosureBMS Deep Dive 2012

1

Battery Charger Design (1S): Key considerations and system design limitations

Miguel Aguirre

October, 2012


2

Agenda

• Single Cell Charger Systems

• Input Considerations and Limitations

• Topology Options– Pros & Cons of Power Path Architecture

• Thermal Issues

• Market Trends Needs vs. Limitations

• Charge Time Optimizer

• Summary and Questions


Single Cell Systems Overview

3

• Single Cell– Most Common Solution for Smartphones (1s) and Tablets (1sXp) today– Allows for simple, low voltage design on the system (Max Battery Voltage

4.35V on some lithium based chemistries)– Simple design to charge from a 5V supply as the charger will always

operate in step down mode– Multiple cells in parallel allow for longer run times due to extra capacity

• This will require a higher charge currents to maintain an acceptable charge time. Charge current will be a function of the current capability of the adapter.

1s configuration 1sXp configuration


Input Considerations

• How many input connectors will the device have?– Single Input (i.e. Micro-USB, Proprietary

Connector)– Multiple Inputs (i.e. Micro-USB and Dock

Connector)

• How many input sources will the product support?– USB charging only (Max current: 500mA

for USB2.0, 900mA for USB3.0)– USB charging and/or adapter into single

port• For Micro-USB port, maximum current

supported by adapter is 1.8A• USB specifies maximum current of 1.5A• With a limit on the current, changing the input

voltage allows you to increase your output current

• USB Power Delivery (USBPD) will allow for more power available for charge solutions.

4

Output current change based on input voltage (assume 90% efficiency and 3.6V Battery)


Adapter Power Limits

• Adapter Power Limits Today– Most Smartphones: 5W – 8W– Most Popular Tablets: 10W – 15W

5


6

Current Capabilities of Adapters

• Power sources have their limits– There are situations where the input power source does not have enough

power to supply what the portable device demands– Becoming increasingly important with the standardization of input

connectors such as the Micro-USB– Input current limits and Input Voltage Dynamic Power Management (VINDPM)

provide the functions needed to solve this problem


7

Voltage Input Dynamic Power Management (VINDPM)

• Utilizing full capacity of adapter – VIN Dynamic Power Management (VINDPM)– Loop continuously monitoring the input voltage to the charger– Without VINDPM the device can enter a hiccup mode between power up and

“brown-out” condition– When input voltage drops, device will limit the input current

Device hits VINDPM threshold and input current is reduced

VIN

IIN 500mA / div

1V/divUVLO


8

Voltage Input Dynamic Power Management (VINDPM)

• Utilizing full capacity of adapter – VIN Dynamic Power Management (VINDPM)– Loop continuously monitoring the input voltage to the charger– Without VINDPM the device can enter a hiccup mode between power up and

“brown-out” condition– When input voltage drops, device will limit the input current

IVIN

VIN

VBAT

STAT

Programmed Charge current higher than adapter capability



Power-path vs. Non Power-path Topologies

• Non Power-Path Topology

• The system voltage is always equal to the battery voltage

• No system startup for deeply discharged batteries

• ICHARGE is always split between IBAT and ISYS

• ICHARGE must be programmed to the maximum charge current for the battery cell

• If ISYS > Termination current, then termination will not occur

• IBAT is reduced for any system load

• Reduced charge current extends charge time. Safety timers may expire prematurely

• Power-Path Topology

• ICONVERTER is set to maximize the current from the source.

• More available current to system and battery charging for faster charge time

• IBAT is set independent of ICONVERTER

• For low system loads, ICONVERTER is reduced to maintain proper charge current

• IBAT is always known by charger• Accurate termination current

• Safety timer extended when charge current is less than programmed value

9

Charger

SystemLoad

ICHARGE ISYS

IBAT

Converter

SystemLoad

Charger

ICONVERTERISYS

IBAT


10

Dynamic Power-Path Management (DPPM)

• Function that monitors the input current, input voltage and output currents of a Power-Path device and automatically gives priority to the system when the adapter can not support the system load

• See following example of DPPM function in a linear charger. Same principle allies for switching chargers. Assume 5W adapter (5V, 1A)

ISYS=0.5A

IBAT=0.5A

IIN≈1A


11

Dynamic Power-Path Management (DPPM)

• Function that monitors the input current, input voltage and output currents of a Power-Path device and automatically gives priority to the system when the adapter can not support the system load

• See following example of DPPM function in a linear charger. Same principle allies for switching chargers. Assume 5W adapter (5V, 1A)

IIN≈1A ISYS=0.8A

IBAT=0.2A


VINDPM and DPPM working together

VIN 5V Adapter

rated for 750mA

IIN

VSYS

IBAT

ISYS

750mA Charging

Supplement Mode

750mA Charging

1.2A Load Step

Adapter Voltage Falls due to Adapter Current Limit

Input Current Reduced by VINDPM function to Prevent Adapter from Crashing


13

Does VINDPM = DPPM?

• No. VINDPM prevents the adapter from hitting a “brown-out” condition. However, the charger will not know how much current is going to the system and how much current is going to the battery.– A charger can have VINDPM and not have Power-path (DPPM)

– Charge current and system current is combined and the charger does not know how much current is being delivered only to the battery

• DPPM allows the charger to know exactly how much current is going to the battery.– With this information, the charger can reduce the charge current and extend

the charging safety timer in the even the system demands higher currents

• Which one is better?– Both topologies allow to charge the battery. Non DPPM chargers will require

the host to measure exactly how much current goes to the battery for proper termination


Time

ICHG

ICHG_THRM

Tj = 1250C

VIN

Thermal Regulation and Protection Loops

Thermal management functions:• Regulate IC junction temperature by reducing charge

current , AND • Turn off the charger when IC junction temperature is

excessive• Slow down the safety timers when the charge current is

reduced by the thermal loop, avoiding a false safety timer fault

Common implementations:• The IC junction temperature is regulated to a value just

below the maximum operating junction temperature, 1250C typical

• The charger is turned off when the Charger IC junction temperature is excessive, 1500C typical

14

PLOSS = (VIN – VBAT) * ICHG


Factors affecting thermal performance (effects on θJA)

15

Case Study: Thermal Effect of PCB design on θJA

Device Size: 2.1mm x 2mm, WCSP

• High K board (no vias), θJA = 69 C/W• Using 2x2 vias, θJA = 45.4 C/W

EIA/JESD 51-1 Standard


Product Thickness and Battery Size: Smartphones

Programmed Charge current higher than adapter capability


HTC One X: 1800mAh, 8.9mm

Samsung Galaxy S3: 2100mAh, 8.6mm

Samsung Galaxy Note: 2500mAh, 10.1mm

16

HTC One X Battery → 4.4mm thick

Galaxy S3 Battery → 5mm thick

Galaxy Note Battery → 6mm thick

Source: TechInsights Teardowns (web)


Working around tradeoffs…• Increasing Battery Size → Larger Charge Current

• Decreasing product thickness → Thinner Inductors → Lower Charge Currents

• 2A – 3A charge current provides sweet spot of short charge times with acceptable inductor sizes– Design for 1.5uH converter stability. Tradeoff between efficiency and

inductor size– Focus on charge time improvements (i.e. Charge Time Optimizer Feature)

4A Inductor2mm height

3A Inductor1.2mm height

17

2A Inductor1.0mm height


Charge Cycle → No CTO

18

83mV OverlapCharge current

reduces too early


Charge Time Optimizer in Action – bq2426x

19

Charge Time OptimizerSharp handoff of CC and CV. Approximately 6mV

overlap – Best in industry

Reduces charge time!

For ITERM = 50mA → Total Charge Time ~4:30 hrs

For ITERM = 250mA → Total Charge Time ~ 3:50 hrs

For ITERM = 500mA (<0.1C) → Total Charge Time ~ 3:10 hrs


Extending Run Time on Power Path Chargers

20

Only 11 mΩ Optional External

FET Driver


Summary

• Charger solutions greater than 3A on smartphones increases the thickness of the design.– Thermal management is a problem with charge currents greater than 3A.

Not enough board space to extract the heat generated on the charger.

• Focus on reducing charge times with Charge Time Optimizer on newer TI chargers (bq2425x, bq2426x)

• Increasing run time by reducing battery discharge path impedance (11 mΩ on bq2426x).

21


Questions?

22

ti confidential – selective disclosure bms deep dive 2012 1 battery charger design (1s): key...

Documents