PowerPath Controllers & Ideal Diodes

PowerPath and ideal diode controllers provide a simple and compact solution to seamlessly switch between multiple power sources such as AC-to-DC wall adapters, USB ports, batteries and redundant supplies. While similar to a power multiplexer, a power source selector or a power distribution switch, Linear Technology’s PowerPath and ideal diode controllers protect the supply by minimizing reverse currents back into the supply and shoot-through currents between supplies. Selection of the power source can be either by highest voltage or by highest priority.

For selection by highest voltage, ideal diodes are employed in a diode-OR configuration. An ideal diode is a controlled MOSFET emulating a diode with a very low forward voltage (< 100mV), saving both power and voltage headroom over conventional power Schottky diodes. The lower drop enables cooler operation, eliminating bulky heat sinks to save board area. External or integrated P-channel MOSFETs are utilized as ideal diodes for load currents below 5A (LTC441n devices), while N-channel MOSFETs handle currents all the way up to 100A (LTC435n). Linear Technology’s ideal diode controller ICs regulate the MOSFET forward voltage in a linear fashion. Compared to comparator based methods, a linear servo ensures smooth, oscillation-free supply switchover and no DC reverse current. If a power source fails or is shorted, a fast

For selection by highest priority, a Prioritized PowerPath controller provides the most general purpose and flexible solution. A Prioritizer, such as the LTC4417, powers the system from the highest priority input that is within its valid voltage window. Typical applications occur in battery-equipped portable products, memory modules with capacitive holdup, and server sub-systems with main and auxiliary supplies.

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