The UCC3956 family of Switch Mode Lithium-Ion Battery Charger Controllers accurately control lithium-ion battery charging with a highly efficient average current control loop. This chip is designed to work as a stand alone charger controller for a single cell or multiple cell battery pack. This chip combines charge state logic and average current PWM control circuitry with a 14 bit counter to program the over charge time. The charge state logic indicates current or voltage control depending on the charge state. The chip includes undervoltage lockout circuitry to insure sufficient supply voltage is present before output switching starts. Additional circuit blocks include a differential current sense amplifier, a 1% voltage reference, voltage and current error amplifiers, PWM latch, charge state decode bits, and a 500mA output driver.