Vout p-p calculations in Webench

FZ37

Other Parts Discussed in Thread: LM25117

I have two very similar designs with only output caps' difference. However, the results showed the opposite direction from what I understand and what from the datasheet of LM25117 page 29. This may not make a lot difference to the design but really like to clear it out. Please help a little detail on how the Vout p-p is calculated in Webench. Thanks,

(1) Vout p-p 9.692 mV with one 560uF Cout.

Design : 4561043/372 LM25117PMHX/NOPB

LM25117PMHX/NOPB 22.0V-26.0V to 12.00V @ 10.0A

(2) Vout p-p 26.382 mV with one 560uF and two 47uF Cout.

Design : 4561043/423 LM25117PMHX/NOPB

LM25117PMHX/NOPB 22.0V-26.0V to 12.00V @ 10.0A

over 9 years ago

0 Surinder Singh over 9 years ago

TI__Expert 3085 points

Thanks for the question. We are looking into this and we will get back very soon.

Regards.

0 Sahil Gupta over 9 years ago in reply to Surinder Singh

TI__Intellectual 1020 points

Hi FZ37,

Can you please share both of your designs with me/or on my email : sahilg@ti.com
I want to look at them and see what are some of the parameter values like fsw, ESR, etc.

thanks
sahil

0 Sahil Gupta over 9 years ago in reply to Sahil Gupta

TI__Intellectual 1020 points

FZ37,

Thanks for sharing the designs.

We realized that the ripple for the mixed output cap in your design should have been lesser compared to the first one.

We are working on fixing the issue.Will let you know as soon it is done.

The datasheet gives an approximate equation for Voutpp, if you want to know how Voutpp is calculated in WEBENCH, you might want to refer to this app note - http://www.ti.com/lit/an/slva630a/slva630a.pdf

Let us know for more questions,

Thanks,

sahil

0 FZ37 over 9 years ago in reply to Sahil Gupta

Intellectual 450 points

Thank you for the clarification. Planning to use one of the designs on a new board.

0 Sahil Gupta over 9 years ago in reply to FZ37

TI__Intellectual 1020 points

Hi FZ37,

The issue has been fixed, please check now.

Thanks

sahil

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Vout p-p calculations in Webench