[FAQ] TPS659037: How should VCC1 and VIO inputs be sequenced?

VCC1 must be provided before VIO is supplied, because otherwise the output of some internal level shifters would be unknown.

Therefore, VIO should be sequenced to ramp after VCC1 is applied. If VIO is generated by the PMIC, this is intrinsically given, but can be accomplished with an external supply as well (e.g. using a powergood signal of VCC1 rail as enable for VIO rail).

Without active discharge, VIO may be discharged slower than VCC1. This is not impacting system-reliability, only negative effect is that it might cause leakage from VIO (which would ultimately discharge VIO). Except the leakage current, there is no concern even if VIO is supplied up to 3.6V when VCC1=0V.