LM5158-Q1: LM5158-Q1 input and output capacitor select

lin Luke

Part Number: LM5158-Q1
Other Parts Discussed in Thread: LM5156, LM5158

HI,

When I use the WEBENCH Design tool to check LM5158-Q1 with input 6V/ output12V/ 1.2A output current (the same with datashhet reference design).

I find the input and output capacitor's value have huge different compare to datasheet reference deign, Which shall i reference?

Thank you

over 3 years ago

0 Stefan Schauer over 3 years ago

TI__Mastermind 48201 points

Hi Luke,

thanks you for using the E2E forum.

When comparing the two designs i get from Webench 22uF whereas the summed up capacitors on the EVM is 28.2uF.
So there is not really a big difference.

To set the output cap fully to your needs you can check this report.

https://www.ti.com/lit/an/snva941/snva941.pdf

It shows the math to calculate the different components for the LM5156.
It is a little bit different then the LM5158 as it has the sitching FET external.

A similar report for the LM5158 should be available soon as well.

Best regards,

Stefan

0 lin Luke over 3 years ago in reply to Stefan Schauer

Prodigy 80 points

Hi Stefan

If you comparing the output capacitor total value between Webench and datasheet( in page.28), thatWBDesign88.pdf will be 44.1uF and 228.2uF, So is it ok to choose the 44.1uF for output capacitor? Thank you

+1 Stefan Schauer over 3 years ago in reply to lin Luke

TI__Mastermind 48201 points

Hi Luke,

i see now - let me check with the author of the datasheet and come back to you.

Best regards,

Stefan

+1 Yinsong Cai1 over 3 years ago in reply to lin Luke

TI__Expert 7450 points

Hello Luke,

The bulk capacitor may or may not be used depending on your requirement on the load transient performance. The ~40uF ceramic cap is generally ok in your case for the steady state ripple.

Please let us know if there is any question.

Thanks,

Yinsong

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LM5158-Q1: LM5158-Q1 input and output capacitor select