High-accuracy fuel gauging extends to single-cell handhelds

Dallas—Texas Instruments' bq27500 fuel gauge IC extends the company's Impedance Track technology to single-cell lithium-ion batteries for the first time.

Implemented on the host system's board on the so-called “system side” to minimize supporting electronics for the battery pack, the chip predicts battery life with 99 percent accuracy—a performance level that heretofore hasn't been available for today's smaller mobile products.

“As mobile devices add more functionality, such as high-definition video and data transmission, consumers want to operate their devices just like notebook computers and expect to know remaining battery capacity,” said Dave Heacock, senior vice president of the analog and logic business. “Today's announcement builds on TI's innovative battery fuel gauge technology, which is used in millions of notebook computers. Our portable device customers asked to incorporate the technology into their mobile designs—and now they can.”

The Impedance Track technology (see Related Links) in the bq27500 accurately measures data from the single-cell battery to predict remaining battery capacity under all conditions, even as a battery ages. The IC analyzes precise state-of-charge by correlating the battery voltage to cell impedance to adjust remaining state-of-charge up or down a predicted discharge curve.

In contrast, most handhelds today do not accurately gauge remaining battery capacity, says TI, but measure the cell voltage to guess the capacity. Traditional gauging techniques used in some handhelds require static and modeling methods that attempt to compensate for discharge rate, temperature and age of the cell, and must also model self-discharge and other non-measurable currents. These models have an inherent error that's difficult to minimize, according to TI, and the end-user typically won't know how much battery time is left.

The bq27500 directly measures the effect of a battery's discharge rate, temperature, age, and other factors to predict remaining life to within one percent. The chip automatically measures and stores real-time battery impedance values in order to adjust to changes in full capacity as the battery ages. State-of-charge and full capacity are calculated from the voltage and impedance measurements, eliminating the need to relearn from a charge and discharge cycle. The bq27500 provides an accurate reserve energy warning, which allows a system to save data to non-volatile memory at the end of a battery's discharge. In addition, system-side implementation allows the bq27500 to control and manage other main battery management functions, such as battery pack authentication.

Pricing: $1.35 in 1k quantities
Product information:
Datasheet: bq27500

Texas Instruments , 1-800-477-8924,

Related Links:
Click Impedance Track 1
Click Impedance Track 2
Click Fuel Gauge Overview

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