nRF9160 ENABLE Pin Maximum Voltage Specification

[Pertti Kasanen]

I found half of the information I was looking for (minimum voltages) from:
https://devzone.nordicsemi.com/f/nordic-q-a/47546/nrf9160-enable-pin-voltage-specification

What would be the maximum ENABLE pin voltages that can be used a) safely b) without considerable current leakage etc?
(If the information was there, did not find it as there are too many hits when searching for "ENABLE")

The PDK schematics (and OPS figure 113) suggests that maybe it would be ok to use up to the VDD voltage - so even up to 5.5V (or whatever the VDD is). 
Is that OK – or should the ENABLE pin be considered as an IO pin and have the voltage limited to VDD_GPIO?

Pertti

[ketiljo]

The enable pin is referenced to VDD. Vih,min = 1.2 V and Vil,max = 0.4 V. 

[Pertti Kasanen]

I'm still not confident about what we can do and what we should not:

Variant 1: So if we use VDD=5.5V, we can safely use 5.5V for ENABLE?

Variant 2: If we use e.g. VDD=3.3V (from separate power management IC), can the ENABLE voltage be higher than the 3.3V VDD?  Can we use a higher voltage (that could be 4.2V from a Li-Po or 5.0V from a USB?)

Variant 3: if we supply the nRF9160 from a Li-Po battery (=VDD range 3.0V-4.2V), could we still use a USB voltage 5.0V for ENABLE?

[ketiljo]

If the enable pin voltage exceeds VDD, you should use a series resistor to limit the current, 10k should be fine. Absolute max voltage is 7 V.