TPS54620: Vout is unstable

Vincent Chen64988

Expert 4480 points

Part Number: TPS54620

Hi Team,

My customer is using TPS54620 at 12V to 1.1V application. He encountered output voltage is randomly unstable issue.

1. Below is customer's SCH.

2. Below is the unstable voltage waveform.

Usually, it happens at power up at room temperature, once the device get warm and customer reset TPS54620 by pulling down then pulling up EN pin, output voltage become normal.

If output voltage is stable, using freeze spray to cool down the chip that can reproduce voltage unstable problem.

Could team help to review the SCH and this issue, then please provide us the comment. If need any other information or experiment, please let me know.

Thanks very much.

Vincent Chen

over 7 years ago

0 Vincent Chen64988 over 7 years ago

TI__Expert 4480 points

Hi Team,

Attached SCH and waveform again, is there any comment for this issue?

Thanks a lot.

Vincent

0 Vincent Chen64988 over 7 years ago in reply to Vincent Chen64988

TI__Expert 4480 points

Hi Team,

Is there any update for this issue?

Thank you.
Vincent

0 JohnTucker over 7 years ago in reply to Vincent Chen64988

TI__Guru**** 191445 points

Vincent,

Can we see the SW node waveform?

0 JohnTucker over 7 years ago in reply to JohnTucker

TI__Guru**** 191445 points

Vincent,

Your design is only marginally stable at best. My simulation shows only about 12 degrees of phase margin. Try:
R9824 = 1 k
C9794 = 33 nF
C9793 = 100 pF
Let me know if this helps.

0 Vincent Chen64988 over 7 years ago in reply to JohnTucker

TI__Expert 4480 points

Hi John,

Thanks a lot for your comment.
I will ask customer to provide SW node waveform and try the values of compensation circuit that you suggested. Will keep you updated for the test result.

Best regards,
Vincent Chen

Power management

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TPS54620: Vout is unstable