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TAS5754M: Unexpected waveform output

Jesse van der Zouw
Expert 1045 points
Part Number: TAS5754M


I wanted to verify the output power of a Texas Instrument class D EVM (TAS5754MDCAEVM)
After hooking up a 4 ohm test load and a 24V 5A power supply I got the following waveform after the LC output filter (see attachment)

If I reduce the output to <1V the output is what I expected (two out of phase sines)
However, when increasing the volume the individual outputs (yellow/blue, +/-) starts to distort, but the differential signal (purple) seems okay.
Is this a problem? Do I measure incorrectly? My speakers dont seem to clip audibly.

  • 0
    TI__Mastermind 28090 points
    Hi Jesse,

    What you are observing appears to be distortion. However the outputs distortion cancels each other out producing a clean differential signal.

    Based on your oscilliscope y axis scale, you appear to have close to 10Vpp per output? Is this right at when the outputs start distoring?

    Also can you give me details on your system configuration and gain setting?


    Thanks,

    Robert Clifton
  • 0 in reply to Robert Clifton56
    Expert 1045 points
    I used the TAS5754M EVM in standard configuration: 768khz, 20dB. Power supply is 24V 5A, load is a 4 ohm resistor
    I'm measuring the mono output with hybridflow 4 running.

    From what I remembered the individual outputs start to distort at about 1Vpp, and the differential signal at 13Vpp
    If you need exact numbers I can verify this on monday.

    What could be the cause? Am I missing a setting somewhere?
  • 0 in reply to Jesse van der Zouw
    TI__Mastermind 28090 points
    Hi Jesse,

    Actually what you are seeing is completely expected. I tested your setting to verify as well.

    Best Regards,

    Robert Clifton