Battery “Fuel Gauge” IC Gives Reliable Runtimes for Mobile Users

STMicroelectronics has unveiled its latest battery fuel-gauging device featuring patented innovations that improve long-term accuracy. This tiny chip, 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 OptimGaugeâ„¢, an adaptive algorithm that tracks the state of charge and corrects the battery model.

The STC3115 further 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 significantly 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 0.45µA while continuing to monitor the battery, and a 2µA 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.

Key features of STC3115 include: The OptimGauge algorithm, which adjusts the battery charge/discharge model over the battery’s life; Industry-standard I2C connection to application processor; Programmable with different battery profiles at manufacture, for flexibility; Monitors batteries up to 4.5V; Monitors multi-cell packs when used with TS941ILT low-power buffer; Dedicated “battery-present” input simplifies battery replacement. Dedicated alarm output, activated if battery voltage falls below threshold level.

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.