Originally Published MPMN November
2004
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Changes in Battery Capacity Are Accurately GaugedTechnology simplifies designing with batteries
Susan Wallace
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| Texas Instruments’ Impedance Track uses gas gauge technology to analyze a battery’s voltage on a continuous basis. |
A gas-gauge technology calculates the remaining capacity in lithium-based battery
packs. Impedance Track from Texas Instruments (Dallas) claims 99% accuracy
throughout the life of a battery.
“Portable devices continually rely on an accurate reading of remaining
battery capacity, so the system won’t lose data or worse, suddenly shut
down during operation,” says Dave Heacock, vice president of the company’s
portable power management group. “Because current battery-measurement solutions
do not calculate impedance as a battery ages, the resulting error rate may be
over 50% after a few months of use. Impedance Track lets end-users and designers
realize the potential of their batteries, and effectively maintain the most
accurate measurement possible over the life of the battery.”
The technology precisely gauges changes in impedance, or resistance, caused
by battery age, temperature, and cycle patterns to accurately predict run-time
of two-, three-, and four-cell battery packs. Impedance Track sits inside a
Flash-based bq20z8x gas-gauge chipset and analyzes a precise state of change
when a battery pack is in a relaxed state by correlating between the battery
pack’s open circuit voltage and the current state of charge and temperature.
An exact starting position is determined for instant state of charge, and total
capacity is calculated from the amount of capacity that exists. This eliminates
the need for a full charge-and-discharge cycle. For applications such as heart
defibrillators, Impedance Track can provide instant and accurate capacity information
on a continual basis.
The technology relies on a dynamic modeling algorithm to learn how much a battery
has degraded through age, temperature, or usage, and then correlates typical
chemical properties of the anode and cathode system in the battery’s cell.
The system significantly reduces development and implementation setup time required
by OEM designers to ensure proper characterization because large databases of
attributes of battery parameters are not necessary.
Texas Instruments
12500 TI Blvd.
Dallas TX 75243
800/336-5236
www.ti.com
Copyright ©2004
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