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TAS5631B noise on BTL output

Other Parts Discussed in Thread: TAS5631B, TAS5518, TAS5631, TAS5630

Hi Engineer,

I verified TAS5631PHD2EVM and found there is noise on BTL when BTL output level is close to clipped level.

At this point, PWMout signal is not continous. Please see the attached waveform in detail.

Thanks,150904_TAS5631B_PWMout_noise_on_max_output.xlsx

  • Hi user4292685,

    The problem may be tied also to the TAS5518, have you verified that the digital input of the PWM processor is correct?, what are the settings used to configure the EVM? 

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • Hi user4292685,

    The switching waveforms look normal for a device that is entering clipping. When the output begins to clip positive, the TAS5631B begins to skip switching pulses to maintain an output closer to the positive rail. Eventually as it is driven deeper into clipping, you will only see pulses at Fsw/3. These narrow pulses are included to simply maintain a healthy bootstrap cap charge. Some LC filters may begin to react to the lower switching frequency by increasing the ripple. If the resonant frequency of your LC filter is somewhat close to Fsw/3, you will see a pretty large ripple. This should not cause any audible artifacts, since it is well above the audio band. However, you could reduce the Q of your filter or reduce the cutoff frequency if these ripple effects are bothersome. Make sure you have a load connected while making the measurements. An open load will exaggerate the ringing.

    An e2e thread about clip behavior for TAS5630 (basically same as TAS5631) is covered here:
    e2e.ti.com/.../83065

    Recommended reading for Class D filter design:
    www.ti.com/.../sloa119b.pdf

    Regards,
    Jeff Berwick
  • Hi Jeff-san,

    Thank you for useful comment.

    Now it's clear.

    Thanks,