A server hot-swap controller manages the connection of a load to an energized supply. Selection begins with the input voltage range, load capacitance and fault requirements. The controller and its external power components must survive startup and faults together; a controller current rating by itself cannot prove that the circuit is suitable.
Calculate what insertion requires
TI's LM5069 documentation describes a controller for live power connections with inrush control and power limiting. It is a useful example of the distinction between controlling a pass MOSFET and carrying the load current inside an integrated power switch.
Record the bus voltage limits, downstream capacitance, normal current and required startup time. Estimate the charge that must enter the load capacitors, then check the startup waveform against the chosen controller's operating method. Include loads that begin drawing current before startup finishes; otherwise the predicted charging time may be too optimistic.
Qualify the MOSFET and current-sense path
During controlled startup or a fault, the pass MOSFET can experience substantial voltage and current simultaneously. Check its safe operating area for the relevant pulse duration and temperature. A low on-resistance value is useful during normal conduction but does not establish safe linear-mode operation.
Choose the sense resistor from the required trip threshold, tolerance and power dissipation. Review the layout of its measurement connections and the gate-drive path. Include the MOSFET package, copper area and airflow in the thermal evaluation rather than relying on an isolated component rating.
Specify the recovery behavior
Decide whether faults should latch the channel off or allow automatic retry. Check how the server management controller receives status and restores service. Repeated retry into a persistent short must be evaluated for temperature rise and stress on upstream power distribution.
Test insertion, removal, short circuit, brownout and operation at maximum supported load. Capture input voltage, load voltage, gate voltage and current during each event. Define what happens when the downstream board is connected with unexpected capacitance or a load already enabled. These tests turn a proposed alternate controller into an engineering decision supported by evidence.
Frequently asked questions
Is a hot-swap controller the same as an eFuse?
They can address related protection tasks, but integration and operating limits differ. Compare the complete circuit, including any external switch, sensing and fault logic.
Can I select the MOSFET only by current rating?
No. Voltage stress, safe operating area, pulse duration, gate drive and thermal conditions are essential parts of the selection.
Request hot-swap components with bus limits, capacitance, load current and the approved schematic. Stock, price and lead time are confirmed in the quotation.