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Battery ICs protect muticell, Li-based battery packs

Posted: 22 Dec 2006     Print Version  Bookmark and Share

Keywords:power management  gas gauge  battery  Texas Instruments  TI 

Texas Instruments Inc. (TI) introduced several new battery-management ICs, including its next-generation Impedance Track "gas gauge" chipset, to improve battery performance and protect multicell, Li-based battery packs used in notebooks and other systems.

Battery gas gauge
TI's bq20z90 Impedance Track battery gas gauge chipset, which integrates new battery authentication technology, is designed to work with the company's newest analogue front end (AFE) protection IC. Requiring a third fewer components than its predecessor, the 99-per cent accurate bq20z90 chipset was designed with ease-of-use and smallest real estate in mind. The gas gauge closely monitors battery capacity, impedance, cell balance, open-circuit voltage and other critical parameters of a 7.2-, 10.8- or 14.4V battery pack and reports the information to the system host controller over a serial-communication bus.

TI's Impedance Track gas gauge technology, launched in 2004 with the bq20z80 chipset, precisely measures changes in impedance, or resistance caused by battery age, temperature and cycle life, to accurately predict run-time of battery packs with two, three and four cells in series. An exact "starting position" is determined for instant state-of-charge, and total capacity is calculated from the amount of capacity that exists, which eliminates the need for a full-charge and discharge cycle.

The bq20z90 drives a three-, four- or five-segment LED display for remaining capacity indication. For those designs that do not require the display indicator, TI also introduced its bq20z70 gas gauge chipset without the LED display driver.

Safety battery conditions
The bq20z90 is designed to work with TI's new bq29330 AFE protection circuit with two integrated linear dropout regulators to further maximise functionality and reduce external component count. The device uses an I²C communications interface to allow the bq20z90 to monitor safety battery conditions such as voltage, individual cell voltages and cell- balancing data, and report the information to the host system.

A designer can program critical safety parameters such as current protection thresholds and delays into the bq29330 to increase flexibility of the battery management system. The device also provides protection for overload short-circuit in charge and discharge conditions, while providing battery cell overvoltage and undervoltage protection.

Unsafe battery identification
The bq20z90 integrates SHA-1, 128bit decryption functionality, which easily identifies potentially unsafe batteries not approved by OEMs for use in their devices. If the battery information checks out, the system can allow normal system operation with the battery pack. A manufacturer can program the system to take action to protect the consumer if the battery pack response is not correct, or if the battery pack is not approved or determined to be defective. In addition, TI introduced a bq26100 protection device for those designers who prefer a discrete implementation of the SHA-1 protection feature.

In addition to the new battery gas gauge chipset, TI has developed a unique development platform aimed at battery pack suppliers. The company's new bqMTester smart battery development board simplifies production of battery modules at a fraction of the cost. bqMTester eliminates the need for an onboard computer and expensive calibration/traceable power supplies and electronic loads. It calibrates and programs electronic smart battery modules based on advanced battery fuel gauges, such as the bq20z90, bq20z80 and bq20z70 devices with Impedance Track. In addition, bqMTester makes tracking battery modules in production easier by programming serial number, date, pack lot code and other defaults.

Pricing and availability
The bq20z90 and bq20z70 gas gauge chipsets, bq29330 protection AFE and bq26100 authentication circuit are available in volume production from TI and its authorised distributors. The bq20z90 is packaged in a 30-pin TSSOP, the smaller bq29z70 in a 20-pin TSSOP, the bq29330 in a 30-pin TSSOP package and the bq26100 in a tiny, 6-pin SON package.

Suggested resale pricing in 1,000-piece quantities is Rs.150.22 ($3.30) for the bq20z90, Rs.132 ($2.90) for the bq20z70, Rs.66 ($1.45) for the bq29330 and Rs.59.18 ($1.30) for the bq26100.

Evaluation modules for the bq20z90 gas gauge chipset, the bqMTester development board, reference designs, application notes and technical documentation are also available.

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