DESCRIPTION
The LTC®4057 is a constant-current/constant-voltage linear charger for single-cell lithium-ion batteries. Its ThinSOT^TM package and low external component count make the LTC4057 especially well suited for portable applications. Furthermore, the LTC4057 is specifically designed to work within USB power specifications.
No external sense resistor is needed and no blocking diode is required due to the internal MOSFET architecture. Thermal feedback prevents overheating by regulating the charge current to limit the die temperature during high power operation or high ambient temperature conditions.
The charge voltage is preset at 4.2V and the charge current can be programmed externally with a single resistor.

FEATURES
■ Programmable Charge Current up to 800mA
■ No External MOSFET, Sense Resistor or Blocking Diode Required
■ Constant-Current/Constant-Voltage Operation with Thermal Regulation Maximizes Charge Rate Without Risk of Overheating*
■ Charges Single Cell Li-Ion Batteries Directly from USB Port
■ Preset 4.2V Charge Voltage with ±1% Accuracy
■ Current Monitor Pin for Charge Termination
■ 25µA Supply Current in Shutdown Mode
■ Low Battery Charge Conditioning (Trickle Charging)
■ Soft-Start Limits Inrush Current
■ Available in a Low Profile (1mm) SOT-23 Package

APPLICATION
■ Wireless PDAs
■ Cellular Phones
■ Portable Electronics