The LTC4057 is a constant-current/constant-voltage linear charger for single-cell lithium-ion batteries. Its ThinSOT™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.When the input supply (wall adapter or USB supply) is removed, the LTC4057 automatically enters a low current state, dropping the battery drain current to less than 2µA. With power applied, the LTC4057 can be put into shutdown mode, reducing the supply current to 25µA.For the standalone version (on-board charge termination) of the LTC4057, refer to the LTC4054.ApplicationsWireless PDAsCellular PhonesPortable Electronics