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TPA2039D1: AMP pollute VCC issue

TSRDM
Prodigy 690 points
Part Number: TPA2039D1

Hello Audio Amplifier Team, can you please help provide feedback on the below issue from our customer?

 

"We have a class D AMP output "pollute the power supply issue". We use TI Class D amp "TPA2039D1YFF".

In our application, we use +5V from USB host and the +5V will also be used for other circuitry like audio preamp. Once the amp output is high, there will be a second harmonic reflect to the +5V power rail.

 

Here is a sample photo for you reference. The input signal is 1k sine wave, the audio output is about 1w@4R+33uH dummy load. You will see the 2kHz ripple(300mV pp) on the power supply rail of 2039.

 

I checked the demo kit of 2039 and also looks similar.

Do you have any suggestion to improve this? Or any suggestion to change to a good class D AMP?"

 

Please see attachment for the waveform.

 

Thank you.

  • 0
    Guru 140200 points
    Hi Dave,

    having a look into the datasheet of TPA2039 you will notice, that this amplifier is intended to be powered by a battery? This would explain the rather small recommended decoupling capacitance of 10µF. Me thinks that this capacitance is much too small when the TPA2039 is powered by voltage regulator instead. So, I would first try to increase the decoupling capacitance of TPA2039 before switching to another chip.

    Kai
  • 0
    TI__Mastermind 20085 points
    Hi Dave,

    This seems to be a decoupling problem. TPA2039D1 is a Class-D audio amplifier that requires adequate power supply decoupling to ensure the efficiency is high and total harmonic distortion (THD+N) is low.
    It would be useful if you can provide me a schematic to review it.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer
  • 0 in reply to José Luis
    TI__Prodigy 690 points

    Hi, we asked for the schematics, will advise. We did get the following paraphrased:

    "For our application, we use USB(connected to PC) power supply for the this Class AMP and we have limitation to increase the decoupling caps. Because of the I-rush issue.

    I use 1k sine wave input and output level is 1W@4R.

    I had tried increasing the decoupling cap to 220uF or even 470uF. There is improvement but ripple is still high.

     

    As you mentioned, I had tried with a good regulator(LTC3127EDD, 5v to 4.5v) between USB input and AMP power supply. The ripple is nearly gone at the 5V side. But still high at 4.5V side.

     

    Any comments?"

     

    Thanks,

  • 0 in reply to TSRDM
    Guru 140200 points
    Hi Dave,

    1W at 4R means a load current of 0.71Ap!

    Kai
  • 0 in reply to kai klaas69
    TI__Prodigy 690 points
    Hi Kai, can you please be more precise in your response, You write that at 1W at 4R means a load current of 0.71Amp! What does this mean for the customer? What are they violating? Thanks,
  • 0 in reply to TSRDM
    TI__Mastermind 20085 points
    This issue is been supporting via email.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer