USB battery charger for Li-ion batteries using FAN5400

Using the FAN5400 integrated switch-mode charger, can be designed a very simple single-cell USB battery charger Lithium-ion (Li ion) charging solution . FAN5400 charger circuit can be designed for charging 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 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 FAN5400 charger circuit (IC) automatically restarts the charge cycle when the battery falls below an internal threshold and 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.

As you can see in this circuit this Li-ion charger require use few external components and can be a good solution for compact electronic projects .
The maximum input voltage that is accepted by this circuit is around 20 volt DC . The maximum charging current can be up to 1.25 amperes .