The BQ25121A 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 IQswitcher 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 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.

A configurable load switch allows system optimization by disconnecting infrequently used devices. The manual reset with timer allows multiple different 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).Read more