ON Semiconductor FAN5400 family (FAN540X) 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 circuit switch at 3 MHz to minimize the size of external passive components. The FAN540X 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.