SHDN pin driven by logic gate, is it the same as arduino's HIGH/LOW

Using Arduino General Electronics
1

Hi all, possibly very stupid question but I can't quite get it:

I have voltage regulator SC4501 and it is enabled/disabled by SHDN pin (with overscore mark) that is active low as far as I understand, in the datasheet there are few examples how to drive that pin however simplest method is via logic gate, there are no examples how to drive it with microcontroller, is it the same thing as Arduino's HIGH/LOW with pulldown resistor on SHDN pin?

I am asking because I had some issued with it being simply connected to Arduino's digital pin, when arduino was outputting HIGH regulator was enabled, but then I set Arduino's pin LOW regulator did not shut down until I added pulldown resistor. But now I am not quite sure that this is how it supposed to be done properly.

Thanks.

2

Do you have the grounds connected?
Otherwise, it should be working. Try a relay or transistor.

3

It is working, I was just curious if this is a correct method of driving SHDN pin because in datasheet it was saying that if pin is over 1.XX something volts then regulator is enabled if votlage less than 0.4V then disabled, it did not say to tie pin to ground to disable it. So I was really concerned if I am doing it right since when its connected to ground via pulldown resistor voltage will be 0V, right?

4

If the wire to SHDN gets disconnected somehow, the regulator will disable itself because of the pulldown. So that isn't really the best practice.

5

It sounds like you could eliminate the uncertainty by just using a 2N2222 transistor to pull the pin low.

6

Typically they give you the threshold below which it's guaranteed to be off, and the threshold above which it's guaranteed to be on. As long as you're above or below those threshold voltages, and are not exceeding the max voltage on the pin (per datasheet absolute max ratings), it should just work.

As always and as noted above, you need to connect all the grounds together for anything to work.

Isaac96:
If the wire to SHDN gets disconnected somehow, the regulator will disable itself because of the pulldown. So that isn't really the best practice.

It seems like perfectly fine practice to me - assuming that's the behavior you want, which it quite likely is.

7

The datasheet give both the maximum voltage for #SHDN and the threshold voltage which is logic
compatible for 5 and 3.3V logic. We say #SHDN for active low signals in text that doesn't support
an overbar. You'll often see things like #RESET and #EN.

8

alexmg2:
I am asking because I had some issued with it being simply connected to Arduino's digital pin, when arduino was outputting HIGH regulator was enabled, but then I set Arduino's pin LOW regulator did not shut down until I added pulldown resistor. But now I am not quite sure that this is how it supposed to be done properly.

Thanks.

Does setting the pin HIGH with that circuit start the regulator back up? if you blink the pin, does it turn on and off like it should?

Either you have something miswired, or you didn't set the pinMode to OUTPUT. Without a sketch or schematic there's no way to know.

9

alexmg2:
I am asking because I had some issued with it being simply connected to Arduino's digital pin, when arduino was outputting HIGH regulator was enabled, but then I set Arduino's pin LOW regulator did not shut down until I added pulldown resistor. But now I am not quite sure that this is how it supposed to be done properly.

The #SHDN pin takes a few microamps to hold it low, the Arduino output being LOW is guaranteed to cope with
that if the pin was set as an OUTPUT.