The LTC4055 is a USB power manager and Li-Ion battery charger designed to work in portable battery-powered applications. The part manages and limits the total current used by the USB peripheral for operation and battery charging. Depending on the state of the current select pin (HPWR), total input current can be limited to either 100mA or 500mA. The voltage drop from the USB supply or battery to the USB peripheral is typically less than 100mV at 400mA and 20mV at 80mA. Other management features include: automatic switch over to battery when input is removed, inrush current limiting, reverse current blocking, undervoltage lockout and thermal shutdown. The LTC4055 includes a complete constant-current/constant-voltage linear charger for single cell Li-ion batteries. The float voltage applied to the battery is held to a tight 0.8% (typ) tolerance, and charge current is programmable using an external resistor to ground. Fully discharged cells are automatically trickle charged at 10% of the programmed current until the cell voltage exceeds 2.8V. Total charge time is programmable by an external capacitor to ground. When the battery drops 100mV below the float voltage, automatic recharging of the battery occurs. Also featured is an NTC thermistor input used to monitor battery temperature while charging. The LTC4055 is available in a 16-pin low profile (4mm x 4mm) QFN package.