LTC4054L-4.2

The LTC^® 4054L is a complete, constant-current/constant-voltage linear charger for single cell lithium-ion batteries.
Its small size and ability to regulate low charge currents make the LTC4054L especially well-suited for portable applications using low capacity rechargeable lithium-ion coin cells. Furthermore, the LTC4054L is specifically de-signed to work within USB power specifications.

No external sense resistor is needed, and no blocking di-ode is required due to the internal MOSFET architecture.
Thermal feedback regulates the charge current to eliminate thermal overdesign. The charge voltage is fixed at 4.2V, and the charge current can be programmed externally with a single resistor.The LTC4054L automatically terminates a charge cycle when the charge current drops to 1/10th the programmed value after the final float voltage is reached.

When the input supply (wall adapter or USB supply) is removed, the LTC4054L automatically enters a low cur-rent state, dropping the battery drain current to less than 2A. The LTC4054L can be put into shutdown mode, re-ducing the supply current to 25A.

Other features include charge current monitor,undervoltage lockout,automatic recharge and a status pin to indicate
charge termination and the presence of an input voltage.