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TAS5548: PWM Oscillation

Robert Goldansky
Prodigy 70 points
Part Number: TAS5548
Other Parts Discussed in Thread: TAS5634EVM, TAS5634

So far I have been working on a prototype board and comparing my results with a TAS5634EVM board to benchmark my build against. I keep seeing what appears to be oscillations occurring on my PWM waveform. This oscillation also occurs on the TAS5634EVM, but I would argue it is less apparent and does not interfere with the performance of the system.







After a couple seconds it will stabilize and give me a pretty clean PWM waveform that looks really good.

Then it will go back to producing a choppy PWM waveform again. I don't understand why I see this weird oscillation occurring...



TAS5634EVM scope capture of PWM and sinusoidal outputs shown below for reference...



  • 0
    TI__Genius 9200 points

    Robert,

    Please check if the oscillation is synchronized with other channel PWM switching. If yes, then it could be from: (1)the ringing coupled from other channel (2)oscilloscope's probe GND connection wire is coupled by switching node.  Generally saying, this ringing is common behavior of PWM switching, doesn't impact audio performance.

    Dylan

  • 0 in reply to Dylan Yao
    Prodigy 70 points

    Dear Dylan,

    The issue has been resolved. The client accidentally created a pi filter instead of a LC filter by placing the filtering capacitor before the inductor (no good). This caused a short being seen from the TAS5634 and the current sensing triggering a !FAULT causing the system to toggle between Hi-Z and active. Now there is a high voltage seen on the BST capacitors that should idle around ~12VDC...will continue hardware debugging...

    Thank you for the support.

  • 0 in reply to Robert Goldansky
    TI__Mastermind 36410 points

    Hi Robert

        Glad to hear that !

  • 0 in reply to Shadow He
    Prodigy 70 points

    Dear Shadow and Dylan,

    The team continued to debug the prototype and I believe we have cleared the BST issue. We are now sending 235W into a 8 ohm test load. Looking good so far..

    I think its safe to say this issue is resolved.

    Thank you for the assistance and I wish you the best.

    Regards,
    Robert Goldansky