onsemi, Battery Charger IC 21 V Input 3.3 V Output 10 mA, TSSOP-16 16-Pin

The ON Semiconductor ultra low power protection integrated circuit managing lithium-ion batteries from 3 to 5 cells in series with accurate battery voltage indication up to 5 LED outputs. Each cell in the battery pack is monitored for an over-voltage and under-voltage condition. Upon detecting an over-voltage, the ODI pin will assert indicating a fault condition and stay asserted until the fault is cleared. During an under voltage condition, the UDI pin will also assert indicating the fault but will have a pulse width that is pre−set in the protector. Both over and under voltage detections have a hard coded pre-set delay time before fault indication.

Over voltage and under voltage detection