Microchip Technology

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  • Dual-Input Battery Charger

  • Created: Jun 05, 2016

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The usual battery chargers are AC powered devices which employ one power source only, and which limit the choice to charge directly when AC power source is unavailable. The reference design is dual-input battery charger from Microchip that features both MCP73837 and MCP73838, which is a highly independent integrated linear battery charger management controller. The MCP73837 and MCP73838 are Li-Ion and Li-Polymer battery chargers that feature autonomous power source selection, and employ a constant current / constant voltage (CCCV) charge algorithm with selectable preconditioning and charge termination ratio.

The charge output indicates the different state that the MCP73837/8 is processing. When at standby mode, STAT1 (Green LED) and STAT2 (Yellow LED) are at both HIGH states. The precondition, constant current fast charge, and constant voltage mode set the STAT1 on LOW and STAT2 on HIGH. The charge complete status indicates a HIGH on STAT1 and a LOW on STAT2. The reference design focuses to evaluate single-cell Li-Ion battery charge management. The MCP73837 and MCP73838 preset voltage regulation has the accuracy of +0.5% and can select autonomously between AC-Adapter and USB-Port as the power source. For an AC-Adapter powered system, an external resistor (RPROG) sets the magnitude of the charge current up to a maximum of 1A. While for USB-port providing power, the MCP73837 follows the current limit that is set by the USB specification. In USB charging, a mechanical DIP-switch is built in to select high (maximum 500mA) or low (maximum 100mA).

The MCP73837 has the /PG pin which is an open-drain output that outputs LOW whenever the input is above UVLO (Undervoltage Lockout) threshold and greater than the current battery voltage. The MCP73837 and MCP73838 feature also monitoring of battery temperature. It measures the voltage between the THERM pin and Vss pin. It minimizes the charge current based on temperature, thus regulating thermal temperature during high power application results to optimization of charge cycle time. Both the MCP73837 and MCP73838 can be applied also to smart phones, personal data assistants, handheld medical devices, digital cameras and ultra mobile devices.