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TPA3132D2: Audio Input capacitance question

AJ Cheng
Genius 3615 points
Part Number: TPA3132D2


Hello.

We use TPA3132D2 have a question want to consult with you.

We change input Capacitance value C7 / C770 and will Affects the output voltage Vp-p. Can I know why? Thanks for help.

  • 0
    TI__Mastermind 24835 points

    Hi AJ,

    How much value capacitors did you try? Basically the DC block capacitors on the input only changes the HPF bandwidth, please find more info about this in the section 7.3.2 in the datasheet. So for the lower frequency input signal, the output amplitude changes wih the input capacitors.

    Please don't use the voltage divideded resitors network(T9101~R9104) on the input, because it could introduce mismatch on the differential input and then it's very easy to cause pop noise is in single-ended input mode during power-up.

    Best regards,

    Shawn Zheng

  • 0 in reply to Shawn Zheng
    Genius 3615 points

    Dear Shawn.

    Thanks for your reply.

    We setting TPA3132D2 Gain MIN 20 dB but got issue is output sine wave too big will cut high side and low side waveform.

    So we add voltage divideded resitors network and as you said we got POP noise.

    We remove R9102 / R9104 and keep R9101 / R9103 and change C7 / C770 can be solved POP noise and output sine wave too big issue.

    We tested music and 1K Hz is OK. We want to confirm with you if this is possible.

    Right now solution is R9102 / R9104 = remove. R9101 / R9103 = 11K Ohm. C7 / C770 = 1.5nF.

    Some test data are given below for your reference. Thanks for you kindly help~

    1. C7 / C770 = 1nF + R9101 / R9103 = 11Kohm => 1.36Vamp (Output too small)
    2. C7 / C770 = 1.5nF+ R9101 / R9103 = 11Kohm => 1.76VAmp (Right now solution)
    3. C7 / C770 = 2.2nF+ R9101 / R9103 = 11Kohm => 2.28VAmp(Output too big)
    4. C7 / C770 = 3.3nF+ R9101 / R9103 = 11Kohm => 2.6Vamp(Output too big)
    5. C7 / C770 = 1.5nF+ R9101 / R9103 = 0ohm => 1.92Vamp(Output too big)

    Input 1K sine wave, R9102 / R9104 = remove. R9101 / R9103 = 11K Ohm. C7 / C770 = 1.5nF. Input waveform.

    R9102 / R9104 = remove. R9101 / R9103 = 11K Ohm. C7 / C770 = 1.5nF. Output waveform.

  • 0 in reply to AJ Cheng
    TI__Mastermind 24835 points
    Hi AJ,
    Thank you for your update. Is the pop noise within the acceptable range for your solution please? In another word, the pop noise issue and the gain issue can be resolved at the same time, right? Actually we don't recommend users to changing the gain by adapting the input circuit, because the any imbalance on the differential input could be enlarged on the output and cause noise on the speaker, especially this is a single-ended input application. Is it possible to decrease the input signal amplitude?
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Genius 3615 points
    Dear Shawn.
    Thanks for your reply.
    Yes. pop noise issue and the gain issue can be resolved right now.
    I can understand your explanation. However, the amplitude of the input signal cannot be changed.
    Therefore, We chose to change the input circuit.
    If the music test is normal, will there be other risks? Thanks for kindly help~
  • 0 in reply to AJ Cheng
    TI__Mastermind 24835 points
    HI AJ,
    Thanks for your reply. The biggest risk is still the pop noise. The resistor/capacitor tolerence could also cause the imbalance on the differential mode. You need to do the test on many boards to make sure the issues can be fixed on all of them.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Genius 3615 points
    Dear Shawn
    Thanks for help.
    I will test all the PCB boards. About 60~70 pieces. If any question will update for you. Thanks for kindly help~
  • 0 in reply to Shawn Zheng
    Genius 3615 points
    Dear Shawn
    Good day.
    After we remove the R9102 / R9104 and keep the R9101 / R9103 and change the C7 / C770 to 1.5nF, verify that the 60 board is fine.
    We need to know Is the current practice the best solution or have other better solutions can provide to us? Thanks for kindly help.~
  • 0 in reply to AJ Cheng
    TI__Mastermind 24835 points

    Hi AJ,
    Thanks for your update. As I explained sbove, the best solution is to shrink the input signal amplitude. If resistor divider circuit has to be used here, you could select the appropriate resistors and capacitors for the input circuit, as soon as the pop noise is accepatable.
    Best regards,
    Shawn Zheng