Description The FAN54015 combines a highly integrated switch−mode charger, to minimize single−cell Lithium−ion (Li−ion) charging time from a USB power source, and a boost regulator to power a USB peripheral from the battery. The charging parameters and operating modes are programmable through an I2C Interface that operates up to 3.4 Mbps. The charger and boost regulator circuits switch at 3 MHz to minimize the size of external passive components. The FAN54015 provides battery charging in three phases: conditioning, constant current and constant voltage. To ensure USB compliance and minimize charging time, the input current limit can be changed through the I2C by the host processor. Charge termination is determined by a programmable minimum current level. A safety timer with reset control provides a safety backup for the I2C host. Charge status is reported to the host through the I2C port. The integrated circuit (IC) automatically restarts the charge cycle when the battery falls below an internal threshold. If the input source is removed, the IC enters a high−impedance mode, preventing leakage from the battery to the input. Charge current is reduced when the die temperature reaches 120°C, protecting the device and PCB from damage. The FAN54015 can operate as a boost regulator on command from the system. The boost regulator includes a soft−start that limits inrush current from the battery and uses the same external components used for charging the battery.