The UCC3911 is a two-cell lithium-ion (Li-Ion) and lithium-polymer (Li-Pol) battery pack protector device that incorporates an on-chip series FET switch thus reducing manufacturing costs and increasing reliability. The device's primary function is to protect both Li-Ion and Li-Pol cells in a two-cell battery pack from being either overcharged (overvoltage) or overdischarged (undervoltage). It employs a precision bandgap voltage reference that is used to detect when either cell is approaching an overvoltage or undervoltage state. When on-board logic detects either condition, the series FET switch opens to protect the cells.