LM3488: Question about abnormal switching waveform?

Hi 

This is a gentle remind.

Hi David,

Apologies for the delay. Can you provide a number for how many units have shown the defect vs working? Additionally, have you tried A-B-A testing with the IC from a working unit vs a non-working unit? 

Thanks,

Richard 

Hi

Defect rate: 3~4ea occur when 700 units are produced.

Swap A-B-A: When SWAP is tested, it almost follows, but sometimes it is not.

                      So I inquired because there may be circuit problems.

Thanks

Hi David, 

In order to debug, I would first check DR, COMP, FB. Can you grab the screenshots from a working, and non-working unit?

Thanks,

Richard 

Hi

Pls refer to attached file.

002.pdf

Thanks

Hi David, 

Thank you for providing the waveforms. Can you let me know what is the main difference that you see between the working and non-working units? Example: Are the boards being damaged/is it falling out of regulation, but the board is ok?

Thanks,

Richard 

Hi

Board is okay. The switching waveform is different as follows.

Thanks

Hi David,

Sorry for the delay in response. Unfortunately, there is still an insufficient amount of evidence to draw a good conclusion, so may I ask you to clarify the A-B-A test results? Can you take a known working board with a working IC, and then replace the working IC with a "bad" IC and observe the results? 

Thanks,

Richard

Hi

Even if defective IC is applied to other boards, defective waveforms come out as they are.

If IC is defective, can I get a waveform like this?

Thanks

Hi David,

The switch node waveform would imply instability. Can you provide the DR pin waveform?

Thanks,

Richard

Hi

Please refer to the attached file.

File : waveform of #2 COMP, #3 FB, #6 DR

ThanksFail vs Pass.pdf