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PCM5102A: Distortion issues / modulation issues.

Sylwester Sosnowski
Prodigy 10 points
Part Number: PCM5102A

Tool/software:



We have several products based on the PCM5102A and when playing back a sine wave, I can always see some oscillations on the waveform. Looks like it is a sinewave modulated by amplitude.

Is there something that can be done with it? Each DAC uses its own high PSRR LDO.

  • 0
    Prodigy 10 points

    Here is a video to show it a bit better: https://youtu.be/abxMWpqHAx8

  • 0 in reply to Sylwester Sosnowski
    TI__Mastermind 27280 points

    Hi, 

    Our DAC expert is out of office but returns this week and can update your thread.

  • 0 in reply to Sylwester Sosnowski
    TI__Mastermind 30571 points

    Hello,

    Looking at your schematics, there are few improvements that can be implemented in the design of your board.

    • I would add more decoupling caps to supplies including VNEG and LDOO. Use 10uF + 0.1uF
    • Add a dedicated pair of caps for DVDD, it is missing the caps.  These caps should be as close as possible to each supply pins .
    • It is  recommended to put a 22-100 Ohm series resistors for I2S signals.

    This is a simple Hardware controlled DAC, so the issue is external to the DAC. So for set up do the following checks and make sure everything is set accordingly:

    • Make sure your clks are accurate  and valid according to the following equation:          BCLK= # of Ch.  *  Ch depth  * Fs
    •  Refer to Table 11 for BCK Rates (MHz) by LRCK Sample Rate (since PLL is engaged by grounding SCK) 

    Once these correction/verifications are done, let me know if the problem still exists.

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    Prodigy 10 points

    Dear Arash,

    We have 33 Ohm resistors in series for I2S, the I2S signals are coming straight from an ADAT Decoder ASIC.
    There is also 10uF + 100nF on both AVDD and DVDD. We have this issues with the PCM5102A on 2 designs - one using an MCU and one using an ASIC on completely different applications.

  • 0 in reply to Sylwester Sosnowski
    TI__Mastermind 30571 points

    Thanks for the information.

    Since it seems you have the recommended  components, we can concentrate on other possibilities. I have used/tested this part many times and never had any issue with it  and because  you see it in 2 of your different designs, I would like to  start by monitoring the I2S clks .

    Can you please send the DAC a  1KHz sinewave  and plot the I2S signals- all on the same window of the scope so we can monitor their behavior ( similar to figure 14 so we can see One cycle of LRCK with BCK and DIN ) . Please also  provide a zoom in versions with the rising and falling edge of LRCK so  they clearly  show the first few cycles of BLK and Din within each channel) .

    Separately,  can you please plot various supplies including  VNEG, LDOO and both digital and Analog GND.

    And finally can you please provide the exact values for the I2S clks being sent to the DAC.

    Regards,

    Arash