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TPS54202: Questions for TPS54202 Abnormal Power On Output Waveforms

Jacky Wang(QD)
Genius 11580 points
Part Number: TPS54202

Hi Expert,

Our customer is using our TPS54202 for 12V to 5V/1.6A application, and found some abnormal output waveform as below, can you help to check what's the possible reasons and the root cause for this issue?

Customer's schematic and PCB is as below:

Abnormal output voltage waveform during VIN slowly powering up at 1.6A load:

Thanks.

  • 0
    TI__Genius 10070 points
    Hi Jacky,

    The soft-start time should be 5ms, but from the waveform it is within 1ms, that is strange. And the inductor current increases rapidly to current limit, is the load current constant 1.6A?
    From the layout, the wire of feedback loop is too long, and there are too much vias. It is easy to introduce noise and may lead to unstable.
    In addition, did you test other board? Or test with another IC?

    Shawn
  • 0 in reply to Shawn Nie
    TI__Genius 9550 points

    hi Jacky,
    Notice that the device begins to switch when VIN is under 5V.
    Check R1 and R2 value (resistors which connect to EN pin). Suggest optimize these two resistors value and ensure device switch when VIN is higer than 7V. Let us know the test results after you update the R1/R2 value.

  • 0 in reply to Jason Wang (BSR-MV)
    TI__Genius 11580 points

    Hi Jason,

    Thanks for the reply. Actually customer's PCB layout is poor, especially for the ground plane and feedback pull-down resistor. By optimizing these two items as below picture shown, we can close this issue. But we do not know why this poor PCB layout can influence the output voltage which is out of control and having some oscillations, and customer needs us to give them some explanations - can you help on this?

    Thanks.

  • 0 in reply to Jacky Wang(QD)
    TI__Genius 10070 points

    Hi Jacky,

    Good news to know the issue has been solved, the PWM is generate by comparing FB and reference voltage, if there is too much noise on FB, the PWM is irregularity, the system would be unstable.

    Shawn