LM5141: The working principle of skip cycle mode and how does the secondary harmonics happened

Jessica,

I will take a look at this and reply on Monday.

-Sam

Hi Sam,
Thank you so much, look forward to you reply.

Jessica,

It looks like you have subharmonic oscillation at CCM. Are you using the EVM or a custom board? If it's a custom board, please share the layout. We may be seeing some instability which will hurt results.

Let me get you in touch with the expert on this part to answer your other questions.

-Sam

Hi Sam,
Thank you for your reply, I'm using the LM541 EVM do this test.

Jessica,

I will try to reproduce this in the lab.

What changes have you made to the EVM?

-Sam

Jessica,

I don't have one in the lab at the moment. I'll order one.

-Sam

Test EVM.docxHi Sam,

I don't change the EVM, as the attached file shows.

Efficiency test and analysis.pptxHi Sam,

I would like to share more test information with you about this issue. Thank you for your help.

Jessica,

Thanks for all this info. I got EVMs and I've been testing. I'm seeing what you're seeing.

It may be an issue with part sourcing. If the components on the EVM are out of stock then they must be replaced with parts as similar as possible. Sometimes this is not done properly and the operation suffers. I'm in the process of narrowing this down so I'll keep you posted.

-Sam

Sam,

Thank you so much for your kindly help.

Could you please also test the efficiency when the load current is 0.01A, 0.1A,1A,2A,3A and then compare with the datasheet test result(user guide of LM5141). I want to make sure if my test result is correct. These days I want to make sure if the test result is true, so I calculate the efficiency under skip cycle mode. and find the calculate result's tendency almost the same as test result. But the calculate result is lower than test result when load current is low (as the picture attached in my word file). So that let me suspect if my test way have some problem. I attached the test way to you.

I also find when LM5141 work in skip cycle mode, the switching frequency are not regular. I also attached it to you. Maybe this can give you more information to analysis. Thank you so much.   

Jessica.

test way.docxskip cycle mode waveform.docx

Jessica,

I am seeing what you're seeing. We are currently investigating.

-Sam