2 What is Hot Swap?

Hot swap is the replacement or addition of components to a powered system without pausing, powering down, or restarting the system and maintaining normal operation. Preserving normal operation of an I2C bus includes not affecting communication by loading the bus or corrupting an ongoing bitstream. When an I2C node or device is first connected to a system, there is no power supply holding the gates of the internal I2C output FETs to ground, and if the power-up transient on the drain of these pins is fast enough, it may couple to the gate of these output FETs, lifting the gate voltage enough to turn the switch ON momentarily. This, in turn, could reduce bus voltage levels enough to cross the HIGH/LOW thresholds of different devices, resulting in communication errors or data corruption across the bus.

Hot-swapping capabilities help preserve the communication integrity of an I2C bus when replacing nodes or devices, making them most beneficial to high-reliability or zero down-time systems that must be maintained or upgraded while operating. Hot-swappable parts must protect sensitive components against electrical shocks, so using components that are not designed to be hot-swapped or that are partially hot-swappable instead of fully hot-swappable could result in instant errors and possibly hardware failure or damage. To preserve communication during hot-swap events in a system with multiple removable nodes or modules, each removable node must have the ability to be withdrawn and replaced without affecting the operation of any adjacent nodes, regardless of power supply levels and bus activity.