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TPA3112D1 - Ringing heard in speaker?

Andrew Mossman
Prodigy 50 points
Other Parts Discussed in Thread: TPA3112D1

I have implemented the TPA3112D1 and am happy with this part; however, I have implemented an output LC filter to reduce the EMI emitted from the speaker cable wires. Though I am very happy with the results in greatly reducing EMI, I am unfortunately experiencing a constant ringing sound in the speakers (8 ohm). I also am seeing slightly lower gain than specified in the datasheet for the specific gain setting that I am using (gain0 = 1, gain1 = 1).

This is the first time that I have ever used a Class D...I am trying to learn...


Has any one experienced this issue?

and/or

Does anyone have any ideas how I could go about reducing the EMI while at the same time eliminating the ringing noise that I am hearing?

Thank you,

Andrew

  • 0
    TI__Guru**** 189401 points

    Hi, Andrew,

    Obviously, something is seriously wrong here. Can you describe your output filter? Can you post a scope shot of the "ringing" you're seeing?

    If you order one of our EVMs, it comes with an LC filter on it. You could verify the sound is fine on the EVM, then take the output filter and drop it on your board to see if the root cause is indeed the output filter.

    The most common problems with output filters are: choosing an inductor with too low of a current rating and having it saturate, and using a poor quality (eg Y5V) capacitor. For this part, a ceramic cap (X5R or better) is ok.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 50 points

    Hi Don,


    Thank you for your reply.

    I have the chip strapped for mono input with IN- tied to GND through a 150 nF X7R ceramic. At the output, I have a series inductor (IHLP2020CZER150M01) then a capacitor at output of inductor to ground (C3216X7R1E225M). The speaker load (8 ohm) is tied at the output of the inductor also.


    Could you tell me what output filter you would recommend for a 8 ohm speaker load in my configuration?

    Also, what output filter is used on the EVM? I would rather not pay $150 just to find this out.

    Thank you.

    Andrew

  • 0 in reply to Andrew Mossman
    TI__Genius 11680 points

    Hi, Andrew,

    The output filter on our EVM can be viewed here: http://focus.ti.com/docs/toolsw/folders/print/tpa3005d2evm.html and click on 'User Guide'.

    You're using a 15uH inductor and 2.2uH cap. That cap is way too large. It creates a significant gain at high frequencies. You'll likely find that getting closer to the values recommended on our EVM (22uH and .68uF) will eliminate that ringing.

    - Nate

  • 0 in reply to Nate
    Prodigy 50 points

    Hi Nate,

    Thank you for your suggestions.


    I will try this out today sometime and report back.

    Thanks again!

    Andrew

  • 0 in reply to Andrew Mossman
    TI__Genius 11680 points

    Hi, Andrew,

    Great! Be sure to let us know how it goes. :)

    - Nate

  • 0 in reply to Andrew Mossman
    TI__Genius 11680 points

    Andrew,

    Did everything work out?

    - Nate

  • 0 in reply to Nate
    Prodigy 50 points

    Hi Nate,

    Thanks for checking in. Sorry that I didn't respond earlier as promised.

    Actually after doing further testing, I am not so certain anymore that I do NOT have an issue with feedback. We use a complex matrix for configuring mono audio paths and gain settings prior to being input to the PA.

    So, I think that I may have found that this matrix is not being configured properly. In any regard, I do not think that the issue is caused by the output filter as initially thought.


    I do appreciate all the suggestions and support. I will report back once we conclude if it really is feedback or not.

    Thanks again,

    Andrew

  • 0 in reply to Andrew Mossman
    Prodigy 50 points

    Would the ringing due to incorrect LC filter be present even when no audio signal is injected at the input of the amplifier? I have noticed that the ringing only is audible/present when a signal generator is hooked up to the input of the amplifier circuit. The ringing sound is like a high pitch tone in the background of the actual audio.

     

  • 0 in reply to Andrew Mossman
    Intellectual 445 points

    Dear TI E2E Community,

    This thread appears to be exactly the same symptom we are having.  Mr. Andrew Mossman's first and last post seems to indicate the same problem, but this thread focused on the component values of the out filter.

    Our TPA3112 design is based very closely on the EVM schematic.  The output filter components are the same values.  The only differences between the EVM schematic and our schematic pertain to fixed configurations instead of jumpers/pots, and perhaps more importantly, we have quantity 2 TPA3112s on one PCB for stereo operation.  Gain is minimum setting.  We have tried inductors Taiyo Yuden NR10050T220M and TDK SLF10165T-220M2R43PF.

    There is approximately a 425 Hz "ring" with power applied.  This 425 Hz tone is about -65dBV.  The ringing changes very little regardless of whether the input connections are floating, shorted to ground, or shorted together (the input 1uF caps are not bypassed).

    Additionally, we are reviewing the presentation linked-to here

    http://e2e.ti.com/support/amplifiers/audio_amplifiers/f/6/p/60515/216650.aspx#216650

    I'm sure we are doing something incorrectly in layout.  Suggestions are welcomed.

    Kind Regards,

    David