TPS54531 in negative configuration

Dimitri Petrucci

Prodigy 90 points

Other Parts Discussed in Thread: TPS54531, TPS54331, TPS54060A

Hello

Is it possible to use TPS54531 in negative configuration, to get -12V from +15V input?

I'd use another TPS54531 in parallel to get +12V from the same +15V.

If I didn't explain well, I'd like to use TPS54531 with this approach:

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

Yes you can do that. Here are some app notes that explains it. It is applicable to TPS54531:

www.ti.com/.../slva540

www.ti.com/.../slva317

And a calculator tool:

www.ti.com/.../swiftinv-calc

0 Dimitri Petrucci over 8 years ago in reply to JohnTucker

Prodigy 90 points

Thank you.

By looking at those app.notes, it seems that I can't simply "reverse" GND and positive output, instead I should also change the components values and not keep those suggested by the Webench for the positive application, is that right?

0 JohnTucker over 8 years ago in reply to Dimitri Petrucci

TI__Guru**** 191445 points

I would probably use whatever the calculator tool provides. It was designed specifically for inverting buck boost topology. In the past I have used webench for 27 V input to 12 V output to get "close".

0 Dimitri Petrucci over 8 years ago in reply to JohnTucker

Prodigy 90 points

I would use the calculator tool, but TPS54531 isn't listed in the deveice selection menu.

I'm not familiar with the others devices supported, which other one could I use to approximate the calculations? maybe TPS54331?

0 JohnTucker over 8 years ago in reply to Dimitri Petrucci

TI__Guru**** 191445 points

It is probably not too hard to modify the tool to include TPS54531. It might be a couple days before I can do it though as my schedule is rather full. Can you tell me about your application? That way I can prioritize this. If it is sensitive, you can contact me directly at j(dash)tucker(at)ti(dot)com.

0 Dimitri Petrucci over 8 years ago in reply to JohnTucker

Prodigy 90 points

thank you, don't worry, it is not prioritary. I will try to do that, I guess I just need to compare the specs for the TPS54531 and TSP54331 and modify the constants on the sheet

0 JohnTucker over 8 years ago in reply to Dimitri Petrucci

TI__Guru**** 191445 points

I think you cannot modify the constants yourself. They are hidden and locked. I am pretty sure I know the original author. I can possibly get him to make you a version that supports TPS54531 directly.

0 Dimitri Petrucci over 8 years ago in reply to JohnTucker

Prodigy 90 points

you're right, I tried and indeed I cannot modify the consants.
I guess I will use TPS54331 in the meanwhile for tests/prototypes, and then if the calculator will support TPS54531 in the future, I will change for it.

0 JohnTucker over 8 years ago in reply to Dimitri Petrucci

TI__Guru**** 191445 points

probably the most important factor is the difference in gmps...

0 Dimitri Petrucci over 8 years ago in reply to JohnTucker

Prodigy 90 points

I noticed that changing the device in the calculator, doesn't change any component values. The only component that changes is the Cin capacitor, according to Io.
So I'd say I can use TPS54331 using the components suggested by app.note SLVA317 for TPS54060A, since it meets my requirements: 15V min input, -12V output, 0.01% output ripple v. noise, 2A Io
And I think it would give me the same numbers if there was TPS54531 in the list.

0 JohnTucker over 8 years ago in reply to Dimitri Petrucci

TI__Guru**** 191445 points

That is somewhat surprising. I did not personally develop that tool, but I would expect the compensation to change with the varying power stage parameters. I tried a coupe different ICs and notice that you are correct. Very little changes. Let me see if I can track down the author of that tool and find out what is going on.

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TPS54531 in negative configuration