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TPA3123D2 3HZ DUP DUP output

karthik venkatesh
Intellectual 345 points
Other Parts Discussed in Thread: TPA3123D2

Hi,

I am using TPA3123D2 TI power amplifier for my audio application.

I use BTL mode for amplification.

Please refer the attached xls sheet "Subwoofer ckt" for tpa power amp circuit and speaker connections.

Issue I face is:

I constantly get ~3Hz "DUP DUP" sound at the subwoofer speaker output.

Whatever be the input I feed to TPA3123D2 power amp, I get only 3Hz dup dup output.

Possible problem:

#1 The output LC filter values.

I have found more posts in TI forum where they have discussed about output LC filter causing these kind of issue.

Based on those discussions, I tried removing the LC filter at the TPA output and I found 250KHz PWM output at Lout and Rout of TPA power amp, which I guess is the expected behavior. 

I even tried with L=11uH and C=1.3uF at output but still I get 3Hz dup dup output.

Please find the experiments I did for debugging this issue in the sheets of attached xls.

#2. Input pre-amp:

For some reason, I found that bypassing input pre-amp ckt, eliminates the 3Hz dup dup noise.

Setup:

  • Circuit used - Please refer the "Subwoofer ckt" sheet of the attached xls.
  • TPA3123D2 Supply - 15V bench power supply.
  • Pre-amp supply - 15V.
  • Speakers - Two 3" 4ohms speakers (derived by parallel'ing four 3" 8ohm speakers). Refer "Subwoofer ckt" sheet of the attached xls.

Kindly help me in debugging the reason for getting 3Hz dup dup output.

Regards,

Karthik

0003.tpa3123 char.zip

tpa3123 char.zip
  • 0
    TI__Guru**** 189401 points

    Hi, Karthik,

    How strange. It sounds like the problem is with your op amp. When you get the "dup dup" sound, is the PWM contantly running, or is it cycling on and off at a couple hertz?

    Is your VDD/2 bias for the op amp stable? What does the output of the op amp look like on a scope?

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 30 points

    Dear Everybody,

    how did you solve this 3HZ DUP DUP at the end 'cause I am having the exact same issue testing a bright new design.

    Thanks for your help.

    Marc

  • 0 in reply to user3665145
    TI__Expert 6985 points
    Hello Marc! Shawn can help you with your question. But could you also respond with what you are trying to do (e.g. configuration set up, type/load of speakers, PVDD, etc)? This will help Shawn with a response. Thanks, Jeff
  • 0 in reply to user3665145
    TI__Mastermind 24835 points

    Hi Marc,

    Could you please let me know whether you are using the single-ended or differential mode input? Please use differential input mode as much as possible. If you have to use single-ended input mode, please use psedo differential input mode in your PCB layout design. And is there a pre-amp before the audio amplifier? Usually the pre-amp is not necessary and it probably cause asymmetry on the audio input. Any asymmetry on the input could degrade the audio performance. 

    Best regards,

    Shawn Zheng 

  • 0 in reply to Shawn Zheng
    Prodigy 30 points

    Hi Shawn,

    thanks for your answer. My problem doesn't seem to come from the pre-amplifier.

    Even when connecting both L and R inputs of the chip to the ground, the 3Hz dump is still there. It only diseaper once I connect the CS input to ground.

    The power supply is 12Vdc, if I increase it, The IC becomes hot. 24Vdc will destroy it.

    The speakers connected are 4 Ohms.

    The schematic is the one available in the datasheet. All capacitors are ceramic ones except for the 2 470uF going to the speaker.

    I also add 2 more 470uF between VCC and GND.

    The circuit is actually assembled on a bread board for validation before PCB will be realized.

     Kind Regards

    Marc

  • 0 in reply to user3665145
    TI__Mastermind 24835 points

    Hi Marc,

    Thanks for your explanation.

    About the thermal performance, how do you deal with the thermal pad on the bottom of the device on you board? The thermal pad must be soldered to the PCB for proper thermal performance and optimal reliability. Usually the dimensions of the thermal pad and thermal land should be more than 6.46mm by 2.35mm. So it's expected that the system thermal performance degrades if it's not done like this.

    Are you using it in SE mode or BTL mode? It's more sensitive to the layout design in SE mode, comparing to the BTL mode. I think you could try to use it in BTL mode. And please make sure the symmetry on the differential input and output traces. Please also pay attention to the GNDing on your board.

    Best regards,

    Shawn Zheng 

     

     

  • 0 in reply to Shawn Zheng
    TI__Expert 6985 points
    Hello Marc! Did this answer your question? Thanks, Jeff
  • 0
    Prodigy 30 points
    Hi Jeff,

    Yes, we still have a few checks to do but your support helped for sure.

    Thanks again


    Regards


    Marc Vandegaar


    Am 9 août 2017 um 16:09 schrieb "Jeff Kohnle" <bounce-7963@mail.e2e.ti.com>:

     

    A Message from the TI E2E™ Community
    Texas Instruments

     

    Jeff Kohnle replied to TPA3123D2 3HZ DUP DUP output.

    Hello Marc! Did this answer your question? Thanks, Jeff

     
     

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  • 0 in reply to user3665145
    TI__Mastermind 24835 points
    Hi Marc,
    Thanks for your update. Please let us know if you need any help on this.

    Best regards,
    Shawn Zheng