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TPA3255: Operation of the part in slave mode at lower clock frequency

Bill Carlin
Prodigy 110 points
Part Number: TPA3255

I have an application where I need the PWM output frequency to be <100kHz.  I am able to operate the device in slave mode down to ~116.67kHz (700kHz input clock), but I am having difficulty going lower.  I've increased the bootstrap caps for all 4 channels from 33nF to 100nF which seemed to work best.  At 220nF, the lowest clock frequency is 900kHz. 

Is there a way to safely get the device to work at ~100kHz PWM frequency?

  • 0
    TI__Guru 62730 points
    Bill,

    Unfortunately this is outside of our usual operating range so it is hard to guarantee how well or if the part would work.

    We know that THD gets worse as you go slower but it's hard to say how low you could go.

    What's the application here?

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 110 points
    I would like to use the PWM outputs to directly drive (no LPF and no input signal) an ultrasonic transducer (or step up xfmr) at 100kHz. In BTL slave mode, the PWM waveforms are 180° out of phase so they would still act as BTL drive, but I need to drop the clock frequency to 600kHz or slightly lower.

    I did some more testing; increased bootstrap caps to 470nF, no change. Changed GVdd from 9V to 18V, no change. Changed VDD from 48-24VDC, no change. The device stops PWM output at 761kHz, OK at 762kHz. No fault indication.
  • 0 in reply to Bill Carlin
    TI__Guru 62730 points
    Bill,

    I don't have experience using the device outside of audio purposes unfortunately.

    Regards,

    -Adam