Battery "gas gage"

Impedance Track technology from Texas Instruments Inc., Dallas, calculates remaining capacity in lithium-based battery packs with up to 99% accuracy throughout battery lifetime. "Current battery-measurement technology ignores impedance as batteries age, resulting in errors of over 50% after a few months of use," said Dave Heacock, vice president of the company's portable power-management group.

Impedance Track chipsets use a dynamic modeling algorithm to quantify battery degradation —— from age, temperature, or usage —— and then correlate present battery condition to typical chemical properties of the anode/cathode system. The approach allows for the mixing of different cell types in the same battery pack and eliminates the static databases of conventional battery-monitoring devices, says the company.

The two-chip bq20z8x device reports capacity information to the host controller over a system-management bus interface. A host controller, such as a TMS320C55x digital signal processor, manages remaining battery power to extend system run time. The bq20z8x chipset also includes the company's analog front-end chip (bq29312) with an integrated 3.3-V, 25-mA linear-dropout regulator.

Impedance Track initially targets multicell, lithium-based battery packs, but works with nickel-metal hydride (NiMH) and nickel-cadmium (NiCD) chemistries. Single-cell Li-Ion powered smart phones, digital still cameras, and PDAs, are other potential applications.

The bq20z8x chipset with Impedance Track is sampling now with volume production scheduled for late this year. The chipset comes in a 38-pin thin-shrink small-outline package (TSSOP), and the bq29312, in a 24-pin TSSOP package

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