Hot Swapping - Signal Electronics

Signal Electronics

Circuitry attached to signal pins in a hot-swap component should include some protection against electrostatic discharge (ESD). This usually takes the form of clamp diodes to ground and to the DC power supply voltage. ESD effects can be reduced by careful design of the mechanical package around the hot-swap component, perhaps by coating it with a thin film of conductive material.

Particular care must be taken when designing systems with bussed signals which are wired to more than one hot-swap component. When a hot-swap component is inserted its input and output signal pins will represent a temporary short-circuit to ground. This can cause unwanted ground-level pulses on the signals which can disturb the operation of other hot-swap components in the system. This was a problem for early parallel SCSI disk-drives. One common design solution is to protect bussed signal pins with series diodes or resistors. CMOS buffer devices are now available with specialized inputs and outputs that minimize disturbance of bussed signals during the hot-swap operation. If all else fails, another solution is to quiesce the operation of all components during the hot-swap operation.