Enable Pin vs Shutdown Pin

[LukeKnepp]

Hello Everyone, I have a problem here...

I am designing a board that I need a low voltage cutoff for...

I want to use the Enable pin to do this...
I have the circuit designed for a shutdown pin, but this is the opposite of the enable pin, right???

Here is my design in LTSpice...

So here are my 2 questions...

1. What is the difference between Enable and Shutdown Pins?

2. What type of "adapter" do I need to make one work for the other, if that is even possible?

Thank you all in advace for your help!!!

 

[dknguyen]

Enable and Shutdown pins are basically the same thing just named with a different a emphasis. Also consider that such pins can also be either active low or active high. So...
Active LO Enable = Active HI Shutdown
Active HI Enable = Active LO Shutdown

So basically you need the equivalent of a NOT gate with an appropriate output (push-pull or open-collector/drain) depending on what you are driving. This can be accomplished with an actual logic gate or a pull-down transistor + pull-up resistor or a totem pole or whatever.

If you take a look at your circuit there, Q1 and R2 already invert the base of Q1. So if you need to invert it again it you just run your SHTDWN output through another set of those.

 

[LukeKnepp]

Thank you!!

 

[LukeKnepp]

Just like this???

 

[Nigel Goodwin]

Or simply use a PNP transistor, and invert the entire single transistor version.

 

[LukeKnepp]

invert the entire single transistor version.

How do I do that?????

 

[Nigel Goodwin]

How do I do that?????

Turn the entire circuit upside down, and replace the NPN with a PNP. D1 will still need to be the same way though, positive upwards.

 

[dknguyen]

Just like this???

View attachment 119406

yes. You may need to adjust R2 since it now acts as a pull up (for Q1 as it did before) and a base resistor for Q2.

 

[LukeKnepp]

Not Working???

Something Wrong???

 

[Nigel Goodwin]

Not Working???

Something Wrong???
View attachment 119409

No completely wrong, the emitter of the PNP needs to be at the top, and the zener needs to be at the bottom - in series with R3.

As I mentioned, essentially the entire circuit is flipped upside down.

 

[LukeKnepp]

Thank you so much!!!!!!!!

 

[Nigel Goodwin]

No problem, it's just a matter of thinking a 'little' outside the box.