The LTC4059/LTC4059A are constant-current/constantvoltage linear chargers for single cell lithium-ion batteries. Their 2mm x 2mm DFN package and low external component count make these chargers especially well suited for portable applications. Furthermore, they are designed to work within USB power specifications. No external sense resistor, MOSFET or blocking diode is required. Thermal feedback regulates the charge current to limit the die temperature during high power operation or high ambient thermal conditions. The charge voltage is fixed at 4.2V and the charge current is programmable. When the input supply (wall adapter or USB supply) is removed, the LTC4059/LTC4059A automatically enter a low current state, dropping the battery current drain to less than 1A. With power applied, they can be put into shutdown mode, reducing the supply current to 10A. The LTC4059A features an open-drain status pin to indicate the presence of an input voltage. The LTC4059 can be used as a constant-current source to charge Nickel cells. Other features include undervoltage lockout protection and a current monitor pin which can indicate when to terminate a charge cycle.