TI Power Management Fuel Gauge Accurately Predicts Battery Life in Smart Phones and Other Handhelds

“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 TI’s high-volume 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 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 analyzes 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 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. Since these models have an inherent error, which is difficult to minimize, an end-user will not accurately know how much run-time remains as the battery ages.

Predicting Remaining Capacity
The bq27500 directly measures the effect of a battery’s discharge rate, temperature, age and other factors to accurately predict remaining life within one percent 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 re-learn from a charge and discharge cycle.

Intelligent Power Optimization
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 run-time 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 optimize 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 non-volatile memory at the end of a battery’s discharge, so work is not lost when battery life runs out.

System-Side Implementation
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.