N+1 ORing controller for redundant power rails
The Maxim MAX8555AEUB is an N+1 ORing MOSFET controller designed to replace discrete diode-OR solutions in redundant power architectures. It drives an external N-channel MOSFET to steer current from the active supply rail while blocking reverse current from a failed or lower-voltage rail. With a 100 ns turn-off delay, the MAX8555AEUB catches reverse-current faults fast enough to keep the output bus within regulation during a supply dropout or short-circuit event.
External FET selection and thermal budget
Because the MAX8555AEUB has no internal switch, the designer selects an external N-channel MOSFET sized for the load current and the worst-case Rds(on) at the maximum junction temperature. The 2 mA supply current is drawn from the higher of the two supply rails. The 1:1 input-to-output ratio means each controller manages a single ORing path; multiple devices are used in parallel for N+1 redundancy.
Sourcing and lifecycle posture
Note that this variant is listed as RoHS non-compliant. If your BOM requires RoHS compliance, confirm the lead-free equivalent (MAX8555AEUB+) before committing the line.