WEBENCH® Tools/TPS55330: boost a negative rail?

Hi Jim,

TPS55330 can't create an output voltage with a larger (more negative) amplitude. You need to choose a buck converter.

Thanks, that makes sense and i had overlooked the title of the article I linked, ha. 

It's actually been quite difficult to find any resources for developing a negative rail boost with a power IC.  All i have found is that one article.

I'm already using an LMR33630 in a few different power scenarios in the same design. It's a buck converter. Would this IC be usable for boosting a negative rail at 1A? 

If so, any guidance would be super appreciated! 

Zack Liu said:

Hi Jim,

TPS55330 can't create an output voltage with a larger (more negative) amplitude. You need to choose a buck converter.

Hi

   Here is an article that talks about using a buck in an IBB application which you can use as a reference

https://www.ti.com/lit/an/slyt286/slyt286.pdf

We will recommend some parts for you shortly.

Regards,

Gerold

Hi Jim,

I think TPS54335A would be a good converter to consider. It has external compensation, and has more than sufficient current headroom (points #1 and 2 in the Converter Selection section on p.2 of the app note). And with your input being -12V, I don't think there is any concern with point #3 on p.2

Let me consult with the TPS54335A experts to see if they have any specific advice on using this device for your negative boost application, or other part recommendations.

Kris

Thank you! I look forward to hearing what you find.

Hi Jim,

The person I contacted is out of office right now, so it may take some time to hear back. We don't see negative boost applications using buck converters very often, so I do have doubts there would be any specific guidance for using this device in a negative boost configuration, beyond what is covered in the app note.

Kris

Thanks Vincent!

That sounds great. I look forward to hearing if you end up with some results. 

On a side note, will negative-to-negative operations ever be supported by the WEBENCH design tool? 

Thanks

Jim

Hi Jim

   There are no plans to support negative Vin -to-negative Vout designs in WEBENCH at the moment.

Regards,

Gerold

Hi Vincent,

Any chance you've had a moment to look at what kind of negative-negative configuration would work with the TPS54335A to boost -12 to -15 at 1A?

I appreciate your time, and thank you!

jim

Vincent Zhang(BSR) said:

Hi Jim, Kris,

I don't see problem to use TPS54335A to configure as negative boost, but we can try on our EVM and feedback to you next week.

Hi Jim,

   Vincent will get back to you on this.

Regards,

Gerold

Hi Jim,

     Vincent is trying to confirm this on the bench and will reply back with the results.

Regards,

Gerold

That's terrific, thank you!!

Hi Jim,

I'm trying to check on EVM but seems the negative boost is not same buck-boost, which means we need to change the layout if want to verify the performance.

I draw a simplified schematice about how to configure TPS54335A to negative boost converter, hope it helps.

Using TPS54335A to configure as Negative boost.pdf

Hi Jim

   I would not recommend go down the WEBENCH approach for this specific topology.

regards,

Gerold