The Solenoid Common pin on our PMC controllers is used for the protection of the Output MOS-FET's from spikes generated by inductive loads. When an inductive load switches off the inductor tries to maintain the current as the field collapses and this can produce extremely high voltages.

By connecting the sol_com pin to the same voltage that supplies the load any high voltage will be clamped to the supply rail by the internal diodes in the controller. Each MOS-FET has a diode connected to it.

The controllers internal diodes are not designed to protect the load and diodes/capacitors/vdr's at the source are always the best solution and should be used to ensure a stable system.