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.