2.3 Battery Charger

The battery charger for the 2-cell lithium-polymer battery is an MCP73844 dual cell Lithium Polymer charge management controller. It uses an external pass transistor (NDA8434 P-channel enhancement MOSFET) to provide up to 6A of charging current, but the 100m Ω sense resistor R6 limits the charging current to 1.1A. The device also includes several safety times regulated by the 0.1 µF capacitor on pin 5. In addition to the constant current/constant voltage charging function, the device includes an enable input to disable the device, an Undervoltage Lockout and a charge status output. Both the enable and the status output will be connected to the microcontroller to manage the operation of the charger. The balance of the charger design is taken from the data sheet for the device.