This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2500: Humming Noise when load is connected

Part Number: TPS2500

Hi,

We are using TPS2500 in one of our design. We are noticing a humming noise when the load is connected to USB output( Connected Pendrive). Please let us know if there a way to filter out this noise. a snap of the design is attached for your reference.

  • Hi, Gireesh,

    You mean the inductor sounds or VBUS ripple? What's your test condition? Vin, Load?

    Regards,
    Bob
  • Hi Bob,

    We are able to hear an audible humming noise and during debugging we have seen ripple in VBUS also.

    We have connected 3.7V battery voltage as VIN for TPS2500 IC.

    We had tried out devices like USB thumb drive(pen drive), mouse & mobile in charge only mode(SDP mode). we have found that the humming noise is predominant when pen drive's are connected and it was less when a mouse was connected & very less audible when mobile in charge only mode connected.
    We have also found that amplitude & ripple frequency of VBUS varies when the load is changed(different device connected) & No humming noise was observed in the no-load condition.

    Please suggest us a way to filter out the humming noise.

    Regards,

    Gireesh

  • Hi, Gireesh,

    I am clear about your problem.
    From my understanding, the humming noise is coming from inductor. When the low frequency(in audio frequency) periodical current flow through inductor, it will cause magnetic field, and the magnetic field will cause noise. There are 2 solutions for your reference:
    1. Increase Cap on AUS pin(C74).
    2. Try a better inductor.

    If these two solutions can't resolve the noise, please tell me below information for my easier analysis:
    1. What's your Vin.
    2. What's the charging current of pen drive, mouse & mobile phone. If you can't measure it, please arrange it from big to small.
    3. What's your Vin. When you change Vin>4.35 or Vin<4.35, will the noise change?

    Regards,
    Bob
  • Hi Bob,

    we have tried your suggestions, we have placed one more 22uF in parallel to C74(22*2=44uF) & we have tried with multiple inductor values like 2.2uH,4.7uH(different make)& 10uH. But in both the case the humming noise issue persists.

    Below are the information for your analysis.
    1)We had provided Battery voltage to Vin of TPS2500 IC.T he battery voltage can be between 3.5V to 4.2V (3.7 typical). During the time of the test, battery voltage was 3.84V.

    2)we could measure current in few test condition as mentioned below

    *Connected a USB thumb drive(pen drive) which consumes 41mA
    We were able to hear a humming noise. VBUS ripple was measured to be 7.4khz

    *Connected another USB thumb drive which consumes 74mA.
    We were still able to hear humming noise & VBUS ripple was measured to be 3.8khz

    *Connected mobile in charge only mode which consumed 305mA
    No humming noise was produced & there was no ripple in VBUS either.

    *Connected another mobile in charge only mode which consumed 253mA
    No humming noise was produced & there was no ripple in VBUS either.

    3)Since our device is a battery operated "Vin>4.35V" condition doesn't exist.

    In our design, Vin will always be less than 4.35V.

    Regards
    Gireesh
  • Hi, Gireesh,

    From my understanding, at your Vin condition, frequency should be 1MHz. But when load is light, the device work at eco mode. When Load=10mA, the part switches every 200us, so the frequency is 5K, which is in 20Hz-20KHz audio frequency. This will cause humming noise. When load get heavier, this frequency get higher. When frequency get higher than 20KHz, you can't hear the noise anymore.

     

    One possible solution is that try better inductor. What kind of inductor are you using? Can you tell me the partnumber? Can you try the inductor on our EVM?

    By the way, the ceramic cap might generate noise too when low frequency noise is high. The solution is to decrease ripple.

    Regards,

    Bob

  • Hi, Gireesh,

    How is your case? Have you resolved your issue?

    If you resolve your problem, I will close this thread. If you think my answer helped you, please help to click "this resolved my issue" button.

    Regards,
    Bob