What this controller does — and what it doesn't
The MAX5903LCEUT+T is a single-channel hot-swap controller from the Simple Swapper™ family, designed to manage inrush current and protect against overcurrent faults when a board is plugged into a live backplane. It operates from a 9V to 72V supply, drawing 1 mA supply current, and drives an external N-channel MOSFET — there is no internal switch, so the BOM must include the pass FET and a sense resistor. The controller integrates a fault timeout, latched fault output, and thermal limit; once a fault latches, the system needs a manual power-cycle or enable toggle to reset. The undervoltage lockout (UVLO) threshold is programmable with an external resistor divider, letting you set the turn-on voltage for the specific rail.
Where it fits — and where it doesn't
Rated for general-purpose hot-swap applications over -40°C to 85°C, this part suits telecom base stations, 48V distributed-power systems, industrial PLC backplanes, and any board that needs live insertion into a 9V to 72V rail. The SOT-23-6 package keeps the footprint small, but the lack of an internal FET means the external MOSFET and sense resistor add board area. The latched-fault behavior is a deliberate choice: it prevents auto-retry into a persistent short, which is correct for systems where a faulted board should stay off until serviced. If your design needs auto-retry, look at the Simple Swapper parts with an auto-retry option in the same family.
Lifecycle and sourcing reality
The MAX5903LCEUT+T is listed as Active and ROHS3 compliant. No end-of-life notice or last-time-buy window is in effect.