The LM3658 is a single chip charger IC designed for handheld applications. It can safely charge and maintain a single cell Li-Ion/Polymer battery operating from an AC wall adapter or USB power source. Input power source selection of USB/AC is automatic. With both power sources present, the AC power source has priority. Charge current is programmed through an external resistor when operating from an AC wall adapter allowing charge currents from 50 mA to 1000 mA. When the battery is charged using USB power, charge currents of 100 mA or 500 mA are pin-selectable. The termination voltage is controlled to within 0.35% of 4.2V. The LM3658 requires few external components and integrates internal power FETs, reverse current protection and current sensing. The internal power FETs are thermally regulated to obtain the most efficient charging rate for a given ambient temperature.