TI Improves Battery Gauge
By Jessica Davis -- EDN, September 13, 2004
Looking to improve the accuracy of the gauge that lets users know how much battery life is left in their notebook computers or other devices, Texas Instruments is sampling a new product designed to do just that.
TI has developed a dynamic algorithm model that enables 99 percent accuracy in calculating the remaining capacity of lithium-based multi-cell batteries, even after months of use.
"Over the life of the battery, there are things that negatively affect accuracy," said Dave Heacock, vice president of portable power management at the Dallas-based chipmaker. And as the battery ages, the accuracy of the "gas gauge" suffers, with up to a 50 percent error rate after just a few months of use.
TI has patented the technology, which it calls Impedance Track, that can track changes in resistance caused by battery age, temperature and cycle patterns, allowing it to accurately predict run time of battery packs that include from two to four cells. The company is planning volume production in Q4, with end products appearing in Q4 or Q1
It's the first such technology that will be used in notebook computers. TI is also planning silicon for other devices such as cell phones, but wasn't ready to provide a time line for those devices.
The technology relies on a dynamic modeling algorithm, which draws on how much a battery has degraded through age, temperature and usage and then correlates those factors to the typical chemical properties of the anode/cathode system in the battery's cell.
Gas gauges today typically rely on static modeling techniques, which call on huge databases to measure each attribute of hundreds of battery parameters. In addition, by eliminating the databases, the new technology significantly reduces development and implementation set up time required by OEMs, according to TI.
Similar technology has been used in uninterruptible power supplies, but never before on portable devices.
"We've been able to get it down to a single chip," said Heacock. "With a single chip now you can attack portable market place." That single chip goes into the battery pack.
The technology will initially target applications with multi-cell lithium-based battery packs, but it is also capable of supporting other battery chemistries such as nickel-metal hydride or nickel-cadmium.
