What this hot-swap controller does — and what it does not
The Maxim Integrated MAX5903ABEUT+T is a single-channel hot-swap controller from the Simple Swapper™ family. It manages the inrush current and protects against overcurrent faults when a board is plugged into a live backplane. The part controls an external N-channel MOSFET — there is no internal switch, so you size the FET for your load current, not a fixed limit. Supply range covers 9V to 72V, which takes in 12V, 24V, and 48V telecom/industrial rails without a separate bias supply. The controller draws 1 mA from that rail. It is packaged in a SOT-23-6, surface-mount, and rated for -40°C to 85°C, so it fits outdoor telecom cabinets and factory-floor equipment.
Fault handling: auto-retry, timeout, and thermal limit
Three built-in protection features save you from adding a supervisor MCU. Auto-retry means the controller will attempt to restart after a fault clears — useful for transient overloads that clear on their own. Fault timeout prevents the MOSFET from staying on indefinitely during a sustained overcurrent event. Thermal limit shuts things down if the die temperature exceeds the safe operating area. These are hardwired behaviors; no firmware required.
Programmable UVLO — set the brownout threshold yourself
The undervoltage lockout (UVLO) threshold is programmable via external resistors. This lets you match the turn-on voltage to the downstream converter's minimum input, preventing the load from browning out when the backplane sags. No factory-programmed threshold to work around.
Sourcing and lifecycle
The MAX5903ABEUT+T is listed as Active and ROHS3 compliant. No end-of-life notice is on record.