Dallas—Texas Instruments' bq20z90 advanced Impedance Track gas gauge chip for multicell, lithium-based battery packs, for use with the company's bq29330 analog front end (AFE) battery protection IC, uses one-third fewer components than its predecessor.
The gas gauge IC closely monitors battery capacity, impedance, and other critical parameters of a 7.2-, 10.8-, or 14.4-volt battery pack and reports the information to the system host controller over a serial-communication bus. The bq20z90 drives a three-, four- or five-segment LED display to indicate remaining capacity indication. TI's bq20z70 gas gauge chip, without the LED display driver, is also available for designs that do not require a display indicator.
Front-end battery protection
More specifically, the bq20z90, using an I2C communications interface, monitors battery voltage, individual cell voltage and cell-balancing data, and reports the information to the host system. The bq29330 holds critical safety parameters such as current protection thresholds and delays. The system provides protection for overload, short-circuits (both charged and discharge conditions), and battery cell over-voltage and under-voltage protection.
Integrated SHA-1 Based Authentication
The bq20z90 integrates SHA-1, 128-bit decryption functionality, which identifies potentially unsafe batteries not approved by original equipment manufacturers 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 its bq26100 protection device for those designers who prefer a discrete implementation of the SHA-1 protection feature.
Smart Battery Test Board
TI's development platform aimed at battery pack suppliers, the new bqMTester, is designed to simplify the production of battery modules at a fraction of the cost. The bqMTester eliminates the need for an on-board computer and calibration/traceable power supplies and electronic loads. It calibrates and programs 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.
Click here for the bq20z90's datasheet, and here for the bq20z70's. The bq20z90 and bq20z70 gas gauge chipsets, and the bq29330 protection AFE and bq26100 authentication circuit are available in volume production from TI and its authorized distributors. The bq20z90 is packaged in a 30-pin thin shrink small outline package (TSSOP), the smaller bq29z70 in a 20-pin TSSOP, the bq29330 in a 30-pin TSSOP package, and the bq26100 in a 6-pin SON package. Suggested resale pricing in 1,000 piece quantities is $3.30 for the bq20z90, $2.90 for the bq20z70, $1.45 for the bq29330, and $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; click here.
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. Impedance Track calculates changes in impedance to predict remaining run-time within 1 percent accuracy throughout the entire life of the battery. Eliminating the need for a full-charge and discharge cycle, the chip determines the exact "starting position" for instant state-of-charge and calculates total capacity from the amount of capacity that exists.
Texas Instruments, 1-800-477-8924, www.ti.com