• State TI Thinks Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 3 answers
  • Subscribers 32 subscribers
  • Views 626 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

TPA3138D2: some issue and sch review

user5883945
Expert 2066 points
Part Number: TPA3138D2


Tool/software:

Hi

Customer have some issue need some advice

1. If the input exceeds 50%, it will produce a popping sound

2. The filtering capacitor at the power supply point will pull down the supply voltage, causing other voltages in the system to also be pulled down. After removing it, it is OK. When using a voltage regulator to supply power to the amplifier alone, the filtering capacitor will not affect the supply voltage.

The SCH as attachment.

TPA3138D2.pdf

  • 0
    TI__Genius 9195 points

    Hello,

    Does removing the capacitor fix the popping issue as well? And which capacitor is the one that is removed?

    I'd also recommend probing the inputs to the device to make sure the source is not coming before the amp.

    Regards,

    Ramsey

  • 0 in reply to Ramsey Foote
    Expert 2066 points

    Hi,

    There are two issue:
    1. After removing all the filtering capacitors from the 8V7 power supply, the power supply returned to normal; Only one capacitor is connected, and there are issues with the power supply; The customer also tried replacing all capacitors with a 100uF electrolytic capacitor, and it was the same issue;
    Ask the customer to inspect the power board;


    2. After the input signal exceeds a certain value, there will be a popping sound phenomenon at the output end of the power amplifier;
    The customer's main concern now is to solve the second problem

    " I'd also recommend probing the inputs to the device to make sure the source is not coming before the amp"

    The customer does not understand the meaning of this sentence. Can you provide a detailed description.

  • 0 in reply to user5883945
    TI__Genius 9195 points

    Hello,

    The TPA3138D2 is an analog input device. If you are hearing artifacts on the output, then the goal is to determine what the source of the pop is. If you probe the analog inputs to the device with an oscilloscope, we can determine if the pop is from the input or the amp. I would also recommend probing the outputs to see what the pop looks like on the scope.

    Regards,

    Ramsey

  • 0 in reply to Ramsey Foote
    Expert 2066 points

    Hi,

    Another issue is that the output bottom noise is too high, how to reduce it?
    Customer testing data:
    The bottom noise at the input end is -130dB, and the output is -80dB, When there is no input source, the amplifier has significant noise; The customer conducted two experiments:
    a. Disconnect input channels, leave them suspended and grounded;
    b. Replace the power supply with a DC voltage source;
    Both experiments mentioned above are invalid;

    Figure1 output bottom noise

    Figure2 input bottom noise

    Figure3 DC voltage source bottom noise

    Figure4 board power bottom noise

  • 0 in reply to user5883945
    TI__Genius 9195 points

    Hello, 

    Noise measurements should be done with a 20kHz filter with A-weighting. 

    Common ways of reducing noise are to reduce gain, using low noise capacitors, using differential inputs or AC grounding the ground of a single ended signal at the source, and using multiple values of decoupling caps to cover wider frequency ranges. These are all mentioned in the datasheet for more in depth explanations.

    Regards,

    Ramsey

  • 0 in reply to Ramsey Foote
    Expert 2066 points

    Hi 

      Could you help to review the SCH&PCB, Is there anything that can be improved?

  • 0 in reply to user5883945
    TI__Genius 9195 points

    Hello,

    The schematic looks great. Only note I have on the layout is to improve the grounding. I do not see any ground vias and the ground plane is constricted between the output side and the rest of the device. This is especially notable because the grounds for the output stage are only connected to the plane under the device. This means the ground return path for the outputs needs to go through the restricted area on the top and bottom. Adding ground vias to a ground plane on a lower layer or widening the ground plane on the top and bottom of the image could help.

    Regards,

    Ramsey

  • 0 in reply to Ramsey Foote
    Expert 2066 points

    Hello,

      The customer followed your suggestion and modified the PCB, but the test results showed no significant improvement, and the bottom noise was still noticeable.
    Do you have any other suggestions? Is it feasible to replace the inductance with Ferrite Beams based on the schematic of EVM?

  • 0 in reply to user5883945
    TI__Intellectual 2361 points

    Hello,

    Ramsey is out on travel today. He will provide you a response by Monday. Thank you for your patience.

  • 0 in reply to user5883945
    TI__Mastermind 20541 points

    hi

    i find that the noise level in our datasheet is just close to what you tested.

    so maybe your noise level is just the actual result.

    tks

    jesse