Power Path Controller System using LTC4412 to Switch between Primary and Auxiliary Power

The Power Path Controller System is designed to manage two independent DC power sources—a primary adapter and an auxiliary battery—ensuring continuous power to a load without interruption. At the heart of the circuit is the LTC4412 IC, which acts as a low-loss power controller. It drives a pair of external P-Channel MOSFETs (FDC610PZ) acting as pass switches for the power rails. When the primary power supply is active and healthy, the LTC4412 keeps the primary MOSFET turned on while turning off the auxiliary MOSFET, allowing the adapter to power the load. A 100k ohm resistor is typically used for biasing and configuration settings such as gate control on the LTC4412. If the primary power supply fails or drops below the desired threshold, the LTC4412 senses the voltage drop and rapidly switches the primary MOSFET off while turning the auxiliary MOSFET on. This seamlessly routes power from the battery to the load, preventing any reset or power loss in the downstream embedded system. A large 2200uF capacitor placed on the power rail helps filter voltage ripples, stabilize transients, and provide temporary bulk energy storage during the switching transition. Interconnections between power inputs, the controller board, and the load are securely made via three Relimate connectors, all organized on a neat custom PCB.