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TPA3110D2 - pop noise

Hirotaka Matsumoto
Guru 27525 points
Other Parts Discussed in Thread: TPA3110D2

Hi all

Would you mind if we ask TPA3110D2?

Our customer uses TPA3110D2 with their board.
When the SD is changed from low to high, it occurs pop-noise(shock noise).

Our customer's board is similar to TPA3110D2 EVM.
However there is some difference.(Please refer to the following file.)
6740.20151008_TPA3110D2.pdf

<Cmpared with TPA3110D2>
-There is no C14 and R9?
-They use the inductor insted of the FB.

So, does it cause of pop-noise?
What are C14 and R9 used for?
If you have some advice, could you let us know?

We really need your help.

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Genius 9175 points
    Hello Matsumoto-san,

    Are you experiencing this pop while playing audio when you cycle SD?

    If you cycle SD with audio playing, deepening on where in the input cycle the output turns on, there will be a discontinuity. For example, a SD event on the peak of an input sin wave will cause a transient voltage spike equal to the peak voltage signal across the speaker.
    To minimize pop, it is always recommended to stop the audio signal before putting the device into SD.

    Do you have any oscilloscope photos of the output noise during a SD event?

    Best Regards,
    Matt
  • 0 in reply to Matthew Beardsworth
    Guru 27525 points

    Matt san

    Thank you for your prompt reply and your kindness!

    We are confirming  followings now;
    -Are you experiencing this pop while playing audio when you cycle SD?
    -Do you have any oscilloscope photos of the output noise during a SD event?
    We will feed back after we get some information.

    And then, if you have the effect of C14 and R9 removing and using the inductor instead of FB, could you let us know?

    We appreciate for your help.

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Genius 9175 points

    Matsumoto san,

    The changes made to the output filter including the inductor and the removal of C14 and R9 should have no effect on the pop performance.

    If you are experiencing pop even without music playing, make sure that the input DC blocking capacitors have matched time constants. These capacitors are charged during power on to 3V and due to the differienal input of the amplifier, if the RC charge time of the INP and INN paths are different, pop will often be a heard.

    If the time constant is similar, make sure low tolerance capacitors and resistors are used at the inputs. They should be 5% or better to insure that the charge time is the same on the negative and positive inputs.

    Best Regards,

    Matt

  • 0 in reply to Matthew Beardsworth
    Guru 27525 points

    Matt san

    Thank you for you excellent reply!
    Our customer could solve this problem with chaning the input DC blocking capacitors.
    We appreciate your help.
    And we got that the changes made to the output filter including the inductor and the removal of C14 and R9 should have no effect on the pop performance.

    However our customer asked what C14 and R9 is used for.
    So, at last, could you let us know only this?

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Genius 9175 points

    Matsumoto san,

    I am happy to hear that your customer was able to track down the problem.

    C14 and R9 are called a Zobel network. When driving a loudspeaker, due to the voice coil inductance, the impedance seen by the amplifier increases with frequency. This causes the Q of the output filter to increase and may case ringing and other issues. The C14/R9 Zobel will help flatten this out as its impedance falls at higher frequencies.

    Zobels are also very common in speaker crossover design in a multi-driver speaker enclosure.

    Best Regards,

    Matt

  • 0 in reply to Matthew Beardsworth
    Guru 27525 points

    Matt san

    Thank you for your reply and your cooperation!
    OK, we got it.
    (It seems that Zobel network is the same as snubber circuit.)

    Kind regards,

    Hirotaka Matsumoto