The LTC4012 is a constant-current/constant-voltage battery charger controller. It uses a synchronous quasi-constant frequency PWM control architecture that will not generate audible noise with ceramic bulk capacitors. Charge current is set by external resistors and can be monitored as an output voltage. With no built-in termination, the LTC4012 family charges a wide range of batteries under external control. The LTC4012 features fully adjustable output voltage, while the LTC4012-1 and LTC4012-2 can be pin-programmed for Lithium-Ion/Polymer battery packs of 1-, 2-, 3- or 4-series cells. The LTC4012-1 provides output voltage of 4.1V/cell and the LTC4012-2 is a 4.2V/cell version. The device includes AC adapter input current limiting, which maximizes charge rate for a fixed input power level. An external sense resistor programs the input current limit, and the ICL status pin indicates reduced charge current as a result of AC adapter current limiting. Ideal diode control at the adaptor input improves charger efficiency. The CHRG status pin is active during all charging modes, including special indication for low charge current.