Texas Instruments' bq25120 is a highly integrated battery charge management IC that integrates the most common functions for wearable devices: linear charger, regulated output, load switch, manual reset with timer, and battery voltage monitor. The integrated buck converter is a high-efficiency, low I_Q switcher using DCS control that extends light load efficiency down to 10 µA load currents. The low quiescent current during operation and shutdown enables maximum battery life. The device supports charge currents from 5 mA to 300 mA. The input current limit, charge current, buck converter output voltage, LDO output voltage, and other parameters are programmable through the I²C interface.

The battery is charged using a standard Li-Ion charge profile with three phases: precharge, constant current and constant voltage. A voltage-based JEITA-compatible battery pack thermistor monitoring input (TS) is included that monitors battery temperature and automatically changes charge parameters to prevent the battery from charging outside of its safe temperature range. The charger is optimized for 5 V USB input with 20 V tolerance to withstand line transients. The buck converter is run from the input or battery. When in battery only mode, the device can run from a battery up to 4.65 V.