The LTC4009 is a constant-current/constant-voltage battery charger controller. It uses a synchronous quasiconstant frequency PWM control architecture that will not generate audible noise with ceramic bulk capacitors. Charge current is set by the combination of external sense, input and programming resistors. With no built-in termination, the LTC4009 family charges a wide range of batteries under external control.The LTC4009 features a fully adjustable output voltage, while the LTC4009-1 and LTC4009-2 can be pin-programmed for lithium-ion/polymer battery packs of 1-, 2-, 3- or 4-series cells. The LTC4009-1 provides output voltage of 4.1V/cell, and the LTC4009-2 is a 4.2V/cell version.The device includes AC adapter input current limiting which maximizes the charge rate for a fixed input power level. An external sense resistor programs the input current limit, and theICLstatus pin indicates when the battery charge current is being reduced as a result of AC adapter current limiting.TheCHRGstatus pin is active during all charging modes, including special indication for low charge current.ApplicationsNotebook ComputersPortable InstrumentsBattery Backup Systems