Hi larsen,
At this time the requirement is 0V. We have not yet identified a non-zero threshold value that will work in all cases. So far we have observed a part-to-part variation in the threshold, so while many parts may have a threshold much greater than 0V, we do not have the data to guarantee a threshold >0V that will work for all parts.
The potential consequence is that the SPI communication interface may become unresponsive if the supply is not started from 0V. The behavior is therefore easy to detect, and the corrective action is to restart the supply from 0V.
I hope this helps,
Nitzan