The MCP73837 and MCP73838 devices are fully integrated linear Li-Ion / Li-Polymer battery chargers with autonomous power source selection. Along with its small physical size, the low number of external components required makes the MCP73837/8 ideally suitable for portable applications. The MCP73837/8 automatically selects the USB-Port or AC-Adapter as the power source for the system. For the USB-Port powered systems, the MCP73837/8 specifically adheres to the current limits governed by the USB specification. The host microcontroller can select from two preset maximum charge current rates of 100 mA (low power USB-port) or 500 mA (high power USB-port). With an AC-Adapter providing power to the system, an external resistor sets the magnitude of the system or charge current up to a maximum of 1A. The MCP73837/8 employs a constant current / constant voltage charge algorithm with selectable preconditioning and charge termination. The constant voltage regulation is fixed with four available options: 4.20V, 4.35V, 4.40V, or 4.50V, to accommodated the new emerging battery charging requirements. The MCP73837/8 limits the charge current based on die temperature during high power or high ambient conditions. This thermal regulation optimizes the charge cycle time while maintaining the device reliability.