The X3100 is a protection and monitor IC for use in battery packs consisting of 4 series Lithium-Ion battery cells. The X3101 is designed to work in 3-cell applications. Both devices provide internal over-charge, over-discharge, and overcurrent protection circuitry, internal EEPROM memory, an internal voltage regulator, and internal drive circuitry for external FET devices that control cell charge, discharge, and cell voltage balancing. Over-charge, over-discharge, and over-current thresholds reside in an internal EEPROM memory register and are selected independently via software using a 3MHz SPI serial interface. Detection and time-out delays can also be individually varied using external capacitors. Using an internal analog multiplexer, the X3100 or X3101 allow battery parameters such as cell voltage and current (using a sense resistor) to be monitored externally by a separate microcontroller with A/D converter. Software on this microcontroller implements gas gauge and cell balancing functionality in software. The X3100 and X3101 contain a current sense amplifier. Selectable gains of 10, 25, 80 and 160 allow an external 10-bit A/D converter to achieve better resolution than a more expensive 14-bit converter. An internal 4k-bit EEPROM memory featuring IDLock™ allows the designer to partition and “lock in” written battery cell/pack data. The X3100 and X3101 are each housed in a 28 Ld TSSOP package.