Battery fuel gauge IC offers reliable runtimes for mobile users

February 15, 2013 // By Paul Buckley
STMicroelectronics has unveiled the company’s latest battery fuel-gauging device featuring patented innovations that improve long-term accuracy.

The STC3115 can be used in high-volume handheld electronics and has already been selected by Samsung for some of its recent smartphones. Battery charge indicators – or fuel gauges - have become essential for managing devices such as smartphones, laptops or digital cameras. Accurate ‘time-remaining’ predictions enhance the user’s experience, and can be critical in certain types of portable electronics such as medical devices. Even so, many of today’s fuel-gauging electronics are susceptible to errors caused by battery aging, reduced charging efficiency, leakage, variations in system power demand, and temperature effects.

To enhance fuel-gauging accuracy, ST has combined several important advances in its latest adaptive fuel-gauge IC, the STC3115. Until now, leading devices have used Coulomb counting to monitor energy entering and leaving the battery, and periodic voltage-mode state-of-charge measurements to adjust the Coulomb counter for accuracy. The STC3115 uses both sets of measurements continuously, with OptimGauge, an adaptive algorithm that tracks the state of charge and corrects the battery model.
 
The STC3115 enhances accuracy by measuring true initial battery open-circuit voltage and preventing measurement disruptions when connecting the charger or launching an app. The charging inhibitor is a patented feature that improves accuracy. Aging and temperature compensation are built in, and the voltage measurement accuracy is 0.25%.

Additional value-added features of the new IC include a low-power mode that reduces operating current to only 0.45 µA while continuing to monitor the battery, and a 2 µA standby mode. An Under-Voltage Lockout (UVLO) filter prevents short-term fluctuations in battery voltage from causing unwanted system resets. In addition, the STC3115 saves bill-of-materials costs by operating directly from the battery voltage without requiring its own voltage regulator.

Pricing

The STC3115 is in full production in a 1.4 x 2.0mm chip-scale package, priced from $.95 in quantities of 1,000 pieces.

Visit STMicroelectronics at www.st.com