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TPS543B20: Output power supply issue (High Ripples)

Santosh Singh
Prodigy 130 points
Part Number: TPS543B20

Hello,

We have designed a power supply for the FPGA using TPS543B20 device. The output voltage requirement is 0.85V @ 20A. Input voltage supply is 12V. We have followed the schematic as per WEBENCH simulation . The schematic is attached for your kind reference.

TPS543B20_Schematic.pdf

Our observations regarding the outputs are as follow:

1) When Rramp is 187Kohm, we have seen more than 200mV ripples at the output power supply of 0.85V. The image is attached with name Rramp_187K.

2) When Rramp is 121Kohm, we have seen some improvement in the ripples at the output power supply of 0.85V. The image is attached with name Rramp_121K.

3) We have also changed the Rmode (R301) to 121Kohm and removed Rss (R309). But no improvement in the ripples were observed.

(Note: All the waveform snapshots attached were taken with the bandwidth settings of 20MHz).

Kindly provide your feedbacks in order to reduce these ripples from the output of this device.

Regards,

Santosh

  • 0
    TI__Expert 5446 points

    Hi Santosh,

    The only issue that I noticed in the schematic is the inclusion of the 0ohm resistor for MODE. This should be left open to select the default mode. However, since things do not improve with the addition of a 121kOhm resistor, it is likely that is not driving the issue. Can you please capture waveforms of VIN ripple, SW waveform, and BP voltage so that we can investigate further? The ripple pattern in the shared image is not typical, but I can confirm that the output LC configuration is correct

    Best regards.

    Britton

  • +1 in reply to Britton Jones
    Prodigy 130 points

    Hello Britton,

    We have noticed that when we changed the inductor at the output side to 470nH, these ripples went off and the supply seems to be clean.

    I think this issue resolved without changing anything else.

    Thanks,

    Santosh