Fuel gauge chip claims true accuracy

Battery fuel gauge promises to predict battery charge levels with 99% accuracy.

A new system-side battery fuel gauge IC with Impedance Track technology for smart phones and other handhelds promises to predict battery charge levels with 99% accuracy to extend runtime, protect data and provide a better user experience for mobile handheld users.

"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", says Dave Heacock, Senior Vice President of TI's high-volume analogue 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 bq27500 system-side battery fuel gauge with TI's patented Impedance Track technology accurately measures data from a device's single-cell Li-ion battery to predict remaining battery capacity under all conditions, even as a battery ages.

The tiny IC analyses precise state-of-charge by correlating between a battery's voltage and cell impedance, or resistance, and its current integration to adjust remaining state-of-charge up or down the predicted discharge curve.

Most handhelds today do not accurately gauge remaining battery capacity, but simply measure the cell voltage to guess the capacity.

Traditional gauging techniques used in some handhelds require static and unreliable modelling methods that attempt to compensate for discharge rate, temperature and age of the cell, and must also model self-discharge and other nonmeasurable currents.

As these models have an inherent error, which is difficult to minimise, an end-user will not accurately know how much runtime remains as the battery ages.

The bq27500 directly measures the effect of a battery's discharge rate, temperature, age and other factors to accurately predict remaining life within 1% error.

By measuring and storing real-time battery impedance values, the IC automatically adjusts to changes in full capacity as a 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.

As handheld systems provide more functions, the need has grown for accurate fuel gauging to intelligently manage available power, alert the user of system operating-time, and extend the runtime of the system as far as possible.

Accurate battery data is used by applications processors, such as TI's OMAP3410 processor with SmartReflex power and performance technologies, to optimise the system's complete mobile power operating system.

For instance, the system can leverage low-power modes, clock gating, clock throttling and dynamic voltage and frequency scaling capabilities based on battery capacity.

The bq27500 provides an accurate reserve energy warning, which allows a system to save data to nonvolatile memory at the end of a battery's discharge, so work is not lost when battery life runs out.

The bq27500 is implemented on the host system's board, and can support an embedded or removable battery.

System-side implementation allows a handheld manufacturer to save cost by designing an end-equipment that does not need extra electronics added to the battery pack.

As batteries continue to shrink in size, integration of electronics on the battery becomes more of a challenge.

System-side implementation of the bq27500 can control and manage other main battery management functions, such as battery pack authentication.

The bq27500 is available today in volume from TI and its authorised distributors.

Available in a space-saving 12-pin, 2.5 x 4mm SON package, the device's suggested retail pricing is $1.35 in 1000-piece quantities.

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