Texas Instruments' BQ25125 is a highly-integrated battery charge management IC that integrates very common functions for wearable devices including a linear charger, a regulated output, a load switch, a manual reset with a timer, and a 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 BQ25125 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 including precharge, constant current, and constant voltage. A voltage-based JEITA-compatible battery pack thermistor monitoring input (TS) is included to monitor the battery temperature and to automatically change the charge parameters preventing the battery from charging outside of its safe temperature range. The charger is optimized for a 5 V USB input, with 20 V tolerance to withstand line transients. The buck converter is run from the input or the battery. When it is in battery-only mode, the device can run from a battery up to 4.65 V.

A configurable load switch allows for system optimization by disconnecting infrequently used devices. The manual reset with a timer allows multiple configuration options for wake are reset optimization. A simple voltage-based monitor provides battery-level information to the host in 2% increments from 60% to 100% of the programmed V_(BATREG).