Board-level hot-swap protection in a SOT-23-6
The MAX5903AAEUT+T is a single-channel hot swap controller from Analog Devices' Simple Swapper series, designed to manage inrush current and protect the upstream supply when a board is inserted into a live backplane. It operates from a 9V to 72V supply range and draws only 1 mA quiescent current, making it suitable for 24V and 48V industrial backplanes where the controller's own draw must stay negligible. The part does not integrate the pass FET internally — the external N-channel MOSFET is selected by the designer based on the load current and thermal budget, which gives flexibility for different power levels without changing the controller footprint.
What the ratings mean for the BOM decision
The 9V to 72V input range covers the common telecom -48V rail (nominal -48V, range -36V to -72V) and industrial 24V supplies with margin for transients — no external pre-regulator is needed for these standard bus voltages. Programmable UVLO via an external resistor divider lets the designer set the undervoltage lockout threshold to match the supply's brownout specification — the part stays off until the bus is above the set point, preventing the external FET from operating in the linear region. Auto retry and fault timeout mean the controller attempts to restart after a fault clears, which is useful for transient overloads on a capacitive load; a persistent short cycles the FET until the fault is removed or the input power is cycled.
Package and footprint fit
Housed in a 6-pin SOT-23 package (SOT-6 supplier device package), the MAX5903AAEUT+T occupies about 3 mm × 3 mm of board area — the small footprint fits on the edge of a plug-in card where space is tight.
Lifecycle and compliance status
RoHS3 compliant (2011/65/EU + 2015/863), with no exemptions that would restrict its use in European-market equipment or require a waiver.