The UCC3957 is a BiCMOS three or four cell lithium-ion battery pack protector designed to operate with external P-channel MOSFETs. Utilizing external P-channel MOSFETs provides the benefits of no loss of system ground in an overdischarge state, and protects the IC as well as battery cells from damage during an overcharge state. An internal state machine runs continuously to protect each lithium-ion cell from overcharge and overdischarge. A separate overcurrent protection block protects the battery pack from excessive discharge currents.