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Larger bootstrap capacitor for TPA3122D2

martin haag
Intellectual 400 points
Other Parts Discussed in Thread: TPA3122D2

Hello,

I try to simpify the reproduction of the TPA3122D2. It would help if i could use a 1000nF capacitor instead the recommended 220nF for the bootstrap. Will that work, and will it affect the characteristic of the amplifier?

Best Regards

Martin Haag

  • 0
    TI__Expert 7925 points

    Hi, Martin. I'm sorry we didn't reply to this post months ago when you wrote. If you are still thinking of using the TPA3122D2, I hope I can help with this reply. 

    Capacitance is inversely proportional to the capacitor voltage charging rate, and the bootstrap capacitors are used as a boosted voltage reference for the high side switching rail when they are charged. So, using a larger capacitor will slow how quickly these capacitors charge, and could affect the high voltage of your switching output. The high side switching output should be its peak value for as long as possible (and charging up to it should be as fast as possible) so as to not introduce funny harmonics to the sound. If it's close to a square wave, the output filter will handle it well and convert the output to audio. 1000 nF not an enormous change in capacitance from 220 nF, and the part switches at 250 kHz, so I don't think it will prevent the TPA3122D2 from working, but it could have an effect on performance.

    If you haven't already tried, use the 1000 nF capacitors across the bootstrap and output pins and verify that you get the switching output you want. Or, you can go one step further and verify that the audio output you want is at the correct voltage level and a minimal amount of distortion.

    Good luck,
    Matt 

  • 0 in reply to Matt Lauer
    TI__Expert 7925 points

    Hi, Martin. As a follow-up, larger capacitors around the bootstrap pins could be a reliability concern. The TPA3122D2's bootstrap capacitor charging system was designed around the 220 nF capacitor, and increasing the bootstrap capacitor to 5× its intended value could have repercussions I haven't considered. Just a warning. I would advise you to use the 220 nF capacitors.

    Best,
    Matt

  • 0 in reply to Matt Lauer
    Intellectual 400 points

    Hello Matt,

    thank you for you advice. I will use the recommended 220nF capacitor. Perhaps ill do some testing with the 1000nF by chance.

    Best Regards

    Martin

  • 0 in reply to martin haag
    TI__Guru**** 189401 points

    Martin,

    This is a long term reliability concern, made worse by high temperatures (google electromigration).

    So, unless you have a darnd good reason to use 1000 nF, I suggest you use our recommended value...

    -d2