I have a LM2576 5V voltage regulator and I would like to be able to shut it down from the Arduino. I have gone through the datasheet and cannot find a way to use the ON/OFF pin, which seems to be made expressly for this purpose.
How would I build such a circuit?
Will it be a transistor to ground with a pullup to the input voltage?
You just connect it to a digital pin and run it HIGH.
Is the pin 5V tolerant?
Oh yeah, it just needs to be lower than Vin, no problems there at all. I'm looking at exactly this circuit on my table right now.
Ok, thanks!
No worries 
Stick with those Simple Switchers from TI. They are absolutely fantastic... you can make the most horrid, unforgivable mess of a protoboard layout and they just refuse to stop working. I love them.
I fried my last one shorting something out, so I am being cautious.