The LTC4054L 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 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 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 current state, dropping the battery drain current to less than 2µA. The LTC4054L can be put into shutdown mode, reducing the supply current to 25µA.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.*U.S. Patent No. 6,522,118Max Charge CurrentTrickle ChargeLTC4054-4.2800mAYesLTC4054X-4.2800mANoLTC4054L-4.2150mAYesApplicationsCharger for Li-Ion Coin Cell BatteriesPortable MP3 Players, Wireless HeadsetsBluetooth ApplicationsMultifunction Wristwatches