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TPS7A47: TPS7A4701 output noise

Rock Su
Intellectual 2220 points
Part Number: TPS7A47

Dear colleague,

Our customer is using TPS7A4701, Vin=24V, Vout=18V, Load=0A.

By AC coupling, test is as below. Blue is input, Yellow is output.

Do we have some suggestions?

Thanks a lot!

  • 0
    TI__Mastermind 29180 points

    Hello Rock,

    I did a test on the TPS7A47 EVM.
    If I do not bandwidth limit the output and I use the long oscilloscope ground clip, I see similar results.
    This tells me that I am picking up random noise with the ground clip as the antenna.

    At 20mV per division you will need very good measurement techniques to accurately measure the output.
    The customer could connect the linear regulator to a spectrum analyzer to try to detect the various frequencies in the noise spectrum.
    This would help the customer to eliminate test equipment or other noise sources which are corrupting the measurement.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Intellectual 2220 points

    Dear colleague,

    Thanks for your support!

    And I checked again it with the customer, there may be some misunderstanding.

    Their concern is not the noise, their concern is the noise floating.

    You can see the input is straight, but the output is not straight with low-frequency change.

    Rock Su

  • 0 in reply to Rock Su
    TI__Mastermind 29180 points

    Hello Rock,

    The noise floating can be the result of a poor connection from the oscilloscope to the hardware.
    If you bump the probes during the measurement, that will also affect the noise and cause it to look like the customers waveform.
    It can also be the result of noise coupling into the measurement from other equipment.
    The measurement setup must use low noise techniques to accurately make a measurement at this voltage levels.

    For what it's worth, here is the same measurement using the TPS7A47 EVM.
    I am using the ground clips of the oscilloscope probe in this measurement, to reflect what I believe the customer is seeing.
    Please note that I see the same result when the device is powered or unpowered - demonstrating that the noise is coupling into the EVM from external sources.

    Thanks,

    - Stephen