Stop! Zoom out!

This is your weekly reminder to stop, and zoom out. Fix fixation is foolish.

I've been slammed with a week of unplanned hour here and in-between hour there. Always only enough time to "quickly finish" stuff that deserves a pause. Case in point:

I needed to modify a power supply enable signal, 24V_EN, to be fail safe. That is, if the signal is cut, the power supply needs to shut off. Normally you have to drive the signal to ground (BATT-) to shut the supply down.

Now I want a floating signal to drive the enable to ground.

Easy right? Lemme just quickly chuck in a NOT gate.

Eh, that's ugly. And means I have to negate the logic. And requires a compatible voltage rail. And it just kinda sucks for a number of reasons.

That's alright, I can just quickly fix it with a high side switch.

Not pretty, but now my logic is back to normal and there's no need to match voltage levels.

It's just... messy. Something doesn't feel right. Surely there's something clever I can do here.

It wasn't until I was riding home, for yet another urgent kiddie merry-go-round manoeuvre, that the light bulb went off. Alone with my thoughts and with only my head to work with, I stopped fixating on the fix.

The UVLO isn't required any more. The supply is the last to turn on and the first to turn off, hence the failsafe. So this is the right solution:

Don't fix what you can eliminate instead.