The FAN5401 combines a highly integrated switched-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 3.4Mbps. The charger and boost regulator circuits switch at 3MHz to minimize the size of external passive components.The FAN5401 provides battery charging in three phases: conditioning, constant current, and constant voltage.To ensure USB compliance and minimize charging time, the input current is limited to the value set through the I2C host. Charge termination is determined by a programmable minimum current level. A safety timer with reset control provides a safety backup for the I2C host.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 with leakage from the battery to the input prevented. Charge status is reported back to the host through the I2C port. Charge current is reduced when the die temperature reaches 120°C.The FAN5401 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.The FAN5401 is available in a 1.96 x 1.87mm, 20-bump, 0.4mm pitch WLCSP package.