The MAX5079 ORing MOSFET controller replaces ORing diodes in high-reliability redundant, parallel-connected power supplies. Despite their low forward-voltage drop, ORing Schottky diodes cause excessive power dissipation at high currents. The MAX5079 allows for the use of low-on-resistance n-channel power MOSFETs to replace the Schottky diodes. This results in low power dissipation, smaller size, and elimination of heatsinks in high-power applications.
The MAX5079 operates from 2.75V to 13.2V and includes a charge pump to drive the high-side n-channel MOSFET. Operation down to 1V is possible if an auxiliary voltage of at least 2.75V is available. When the controller detects a positive voltage difference between IN and BUS, the n-channel MOSFET is turned on. The MOSFET is turned off as soon as the MAX5079 sees a negative potential at IN with respect to the BUS voltage, and is automatically turned back on when the positive potential is restored. Under fault conditions, the ORing MOSFET's gate is pulled down with a 1A current, providing an ultra-fast 200ns turn-off. The reverse voltage turn-off threshold is externally adjustable to avoid unintentional turn-off of the ORing MOSFET due to glitches at IN or BUS caused by hot plugging the power supply.
Additional features include an OVP flag to facilitate shutdown of a failed power supply due to an overvoltage condition, and a PGOOD signal that indicates if VIN is either below the undervoltage lockout or VBUS is in an overvoltage condition. The MAX5079 operates over the -40°C to +85°C temperature range and is available in a space-saving 14-pin TSSOP package.
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