The LTC4007 is a complete constant-current/constantvoltage charger controller for 3- or 4-cell lithium-ion batteries. The PWM controller uses a synchronous, quasiconstant frequency, constant off-time architecture that will not generate audible noise even when using ceramic capacitors. Charging current is programmable to 5% accuracy using a programming resistor. Charging current can also be monitored as a voltage across the programming resistor. The output float voltage is pin programmed for cell count (3 cells or 4 cells) and chemistry (4.2V/4.1V). A timer, programmed by an external resistor, sets the total charge time. Charging is automatically restarted when cell voltage falls below 3.9V/cell.