The SWEN pin is a signal which is driven high when the FET must be turned ON. When the SWEN pin is driven low (internally or externally), it signals the driver circuit to turn OFF the FET. This pin serves both as a control and handshake signal and allows multiple devices in a parallel configuration to synchronize their FET ON and OFF transitions.

The SWEN is an open-drain pin and must be pulled up through a 100 kΩ resistance to an external supply generated using the input voltage to the eFuse.

In a primary and secondary parallel configuration, the SWEN pin is used by the primary device to control the ON and OFF transitions of the secondary devices. At the same time, it allows the secondary devices to communicate any faults or other conditions which can prevent it from turning on the primary device.

To maintain state machine synchronization, the devices rely on SWEN level transitions as well as timing for handshakes. This ensures all the devices turn ON and OFF synchronously and in the same manner (for example, dVdt controlled or current limited start-up). There are also fail-safe mechanisms in the SWEN control and handshake logic to ensure the entire chain is turned off safely even if the primary device is unable to take control in case of a fault.