LTC4054

General Description
The LTC4054 is a complete constant-current/constantvoltage
linear charger for single cell lithium-ion batteries.
Its ThinSOT package and low external component
count make the LTC4054 ideally suited for portable
applications. Furthermore, the LTC4054 is s pecifically
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 limit the die temperature during high power
operation or high ambient temperature. The charge
voltage is fixed at 4.2V, and the charge current can be
programmed externally with a single resistor. The
LTC4054 automatically terminates the 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 LTC4054 automatically enetrs a low current state,
dropping the battery drain current to less than 2μA. The
LTC4054 can be put into shudtown mode, reducing he
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.