TPS3702CX33EVM-683: Why is this vibration happening?

Thank you for your inquiry. Are you able to share the schematic for this issue.

Jesse 

Thank you for answer.
The schematic for this issue is this  image. 

Hello,

Looking at the the waveform you had provided, I am assuming that the yellow waveform is the 5V VDD signal, where is the green signal getting probed?

Since it is the VDD signal, have you tried depopulating the TPS3702 to see if the oscillation is still present? I am asking because the ringing at power down is not a documented behavior of this device.

Jesse   

The waveform of yellow line is the 5V VDD signal. 
The waveform of green line is  the  current measured at the blue line in attached image.

Sorry,we have not tried depopulating the TPS3702 to see.

It oscillates after TPS3702(measured at red line in attached image), but not before TPS3702(measured at blue line in attached image).
So, we think the TPS3702 is the cause of  oscillation.

Okay, since the oscillation is detected on the output of the TPS3702, could you please remove the R232 and test again?

Jesse 

When I removed the R232, the oscilltion is green line attached image.

And I am sending the measured image, in which C55 has been changed from 0.1uF to 1uF,  just in case.

Sorry,I test again removed the R232 because oscilltion has noise.

This is correct result.

Thank you for answer.

I have tried mesuring with the R3 changed to 300k, but  the oscillation is still present.

I will have to run some more test, but we are currently in the middle of moving sites and our lab is not going to be ready till December 17.

Jesse 

I understand.
Please run some more test once your move is complete.

I'll be waiting until then.

Thank you for your patients.

Jesse 

Yes,We use TPS3702 series.

However, I wrote the issue about TPS3702cx33EVM-683 ,but in.realy, it was TPS3702cx50.
I apologize for the mistake.

Is this test done on the EVM or a different board?

How is the board/device powered?

Jesse

II'm sorry for not replying earlier.

I was testing on the product board .

And this board is powered 12EVV by AC adapter. 

How are you stepping the 12V down to 5V?

Jesse 

You might want to remove the C55. The decoupling capacitor in combination with the ferrite bead might be causing the issue.

Jesse 

I removed C55 and performed the measurement.

But oscillation is still present.

The 5V is generated on a separate board and supplied to the reset IC through a switch circuit.

Therefore, C55 in combination with the ferrite bead might be unrelated.

I apologize for the lack of information.

Are you able to power the board with another power supply?

Jesse  

Maybe.