The bq24300 and bq24304 are highly integrated circuits designed to provide protection to Li-ion batteries from failures of the charging circuit. The IC continuously monitors the input voltage, the input current, and the battery voltage. The device operates like a linear regulator: for voltages up to the Input Overvoltage threshold, the output is held at 5.5V (bq24300), 5.0V (bq24305) or 4.5V (bq24304). In case of an input overvoltage condition, if the overvoltage condition persists for more than a few microseconds, the IC removes power from the charging circuit by turning off an internal switch. In the case of an overcurrent condition, it limits the current to a safe value for a blanking duration before turning the switch off. Additionally, the IC also monitors its own die temperature and switches off if it becomes too hot.
The IC also offers optional protection against reverse voltage at the input with an external P-channel MOSFET.