DESCRIPTION
The LTC®4009 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.

FEATURES
■ General Purpose Battery Charger Controller
■ Efficient 550kHz Synchronous Buck PWM Topology
■ ±0.5% Output Float Voltage Accuracy
■ Programmable Charge Current: 4% Accuracy
■ Programmable AC Adapter Current Limit: 3% Accuracy
■ No Audible Noise with Ceramic Capacitors
■ Wide Input Voltage Range: 6V to 28V
■ Wide Output Voltage Range: 2V to 28V
■ Indicator Outputs for AC Adapter Present, Charging, C/10 Current Detection and Input Current Limiting
■ Analog Charge Current Monitor
■ Micropower Shutdown
■ Thermally Enhanced 20-Pin 4mm × 4mm × 0.75mm QFN Package

APPLICATIONS
■ Notebook Computers
■ Portable Instruments
■ Battery Backup Systems