Texas Instruments TPS57160 Enable Pin via P-Channel Open Drain Output
As you request, I'll flesh it out to an answer close enough to being acceptable.

If you look at page 4 of the datasheet there's a table of absolute maximum ratings, it also lists the maximum Enable Pin source current as being 100&mu;A.

This means to stay under 1.2V you should certainly keep any resistor to ground below 12k. I'd prefer a smaller one, to be certain, such as 10k.

With a bit more headroom even (and sub 1mA current at "ON" state) you could calculate for 8k2 lower resistor. This would give you: 100&mu;A * 8200 Ohm = 0.82V if the EN pin is the only one sourcing.

This means, that you want, let's say 4V on your EN pin when INH is turned on, because you never dimension for ideal case, you may have power spikes. So even 4V might be too high, but that would depend on your power supply stability and reliability. You can take the Absolute Worst Case Maximum supply voltage and use that for a 5V calculation and then check if at lowest supply the EN will still go a few tenths of volts above 1.2V

which means you calculate for a current of:

4V / 8200 Ohm =~ 487&mu;A

Now, you'd be tempted to subtract the full 100&mu;A from that, and it'll most likely be perfectly good if you do, but since we don't know if that is honest in this case, as we don't know if the current might already be dropping off at that point. It is however safe to assume the EN pin will not bias itself above its own safe point and that the source will turn off at or before 5V is reached, since the Datasheet allows floating pin.

For the sake of argument I'll go compromise here and take away 50&mu;A, which makes 437&mu;A.

The upper resistor now needs to take up 32V at 437&mu;A with your supply of 36V and 4V across the bottom resistor, so the top resistor should be:

Rtop = 32V / 437&mu;A = 73091 Ohm.

Since we took away 50&mu;A at a guess we can round up or down, but 75k Ohm standard value is pretty close.

Add a small capacitor for noise and supply glitch problems, since not much is specified for either chip at switch on or off in sense of input/output glitch suppression, and you get:







simulate this circuit &ndash; Schematic created using CircuitLab

Depending on your turn-on-time requirement versus expected noise and glitches the capacitor can be anything between 1nF and 1&mu;F. Maybe even 2&mu;2 if a dozen or more ms turn-on isn't a problem. Point is, if you design it in, you can easily change it to a higher value or a lower value if the behaviour isn't what you want.

Fun point on the side, a regulator like this, that clearly specifies an internal current source on the EN pin, or even just a weak pull-up, has a very nifty start-delay option. If you connect only a capacitor on its EN pin the internal source will charge it up a while, causing a turn-on delay. Also very convenient if you need supply sequencing and you know how much the production tolerance likely is. (i.e. if it's 50% to 200% of stated value, step your caps in factor-4 at least.)