This document introduces the working principle of the LTC1421 hot swap circuit, which can safely insert or remove the circuit board when the power is on.
The LTC1421 is a device designed for safe hot swapping of circuit boards into live backplanes. It controls positive and negative board supply voltages at a programmable rate, preventing large inrush currents that could damage components or cause system resets. The device includes internal charge pumps to drive external N-channel pass transistors.
They form an electronic circuit breaker that protects against excessive supply current by tripping when voltage across them exceeds 50mV for more than 20us.
The device assumes the board is fully connected when connection sense pins CON1 and CON2 are both forced to ground for more than 20ms.
Pushing S1 generates a hard reset by shorting the POR pin to ground, which cycles the board's power and actively pulls supply voltages to ground.