v-reg ON|OFF control issue

[mikes603]

I'm using a LM2576 switching v-reg that has a ON|OFF port. Which, of course, looks for a high to go off. Now, I'm sending out a 200ms long pulse from my uC (powered from my bench supply so there is no race condition issue). And, looking at the uC output pin with my scope I see that there is in fact a nice (no skew) 200ms pulse.

My issue is when I tie that uC output into my v-regs ON|OFF pin. Once the uC output is wired to the v-reg signal input I no longer see a 200ms pulse, but a short 35ms pulse with skew.

Any idea what is going on here? My v-reg isn't being pulled down enough because it's only getting that short blip instead of the full 200ms I'm generating.

[fcb]

Please post a diagram or sketch. Much quicker for us to understand.

[mikes603]

Please post a diagram or sketch. Much quicker for us to understand.

I'm only running Vin at 5.5v temporarily (I know that's low) so I can run the uC off it and avoid the possibility of a race condition causing my issue.

Excuse my DoodleCAD

[mikes603]

Try using a pull-up see pic from the datasheet below.

That's probably it. The v-regs signal input probably isn't as low Z as i assumed. I'll give a pull-up a go. Thanks.