STEF05: What is the minimum time En/Fault must be held low to reset the device?

Usually you would reset the STEF05 using e.g. a MOSFET, as shown in the datasheet, fig. 4.

The datasheet gives a recommendation how to handle the Enable/Fault pin (section 5.4): "[...]the device can be reset either by cycling the supply voltage or by pulling down the Enable pin below the Vil threshold and then releasing it."

The datasheet also contains the value of Vil.

/Peter

Just to confirm; There is no minimum timing, reset occurs immediately when Enable/Fault is pulled below Vil?

Correct.