Switch-Mode Single Cell Li-ion Battery Charger with USB OTG

The RT9451 integrates a high efficiency USB friendly switch mode charger with On-The-Go (OTG) support for single cell Li-ion and Li-polymer batteries, D+D- detection, and a 50mA LDO regulator into a single chip. The charger features a synchronous 375kHz PWM controller with integrated power MOSFETs, input current sensing and regulation, Minimum Input Voltage Regulation (MIVR), high accuracy charge current and voltage regulation, and charge termination. It charges the battery in three phases : low current pre-charge, constant current fast charge, and constant voltage trickle charge. The input current is automatically limited to the value set by the host. The charger can be configured to terminate charge based on user-selectable minimum current level and automatically restart the charge cycle if the battery voltage falls below the recharge threshold. A safety timer with reset control provides a safety backup for I²C interface. The charger automatically enters sleep mode or high impedance mode when the input supply is removed. The charge status is reported to the host using the I²C interface and the STAT pin. The D+D- detection circuit allows automatic detection of a USB wall charger. If a wall charger is detected, the input current limit will automatically increase from 500mA to 975mA.

In OTG mode, the PWM controller boosts the battery voltage to 5V and provides up to 1.6A of current to the USB output. At very light load, the Boost operates in burst mode to optimize efficiency. OTG mode can be enabled either through I²C interface or GPIO control.