This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

  • TI Thinks Resolved

PCM5102: Driving the hardware IO pins

Intellectual 330 points

Replies: 4

Views: 357

Part Number: PCM5102

Hello,

This is a rather silly question, but when driving IO pins such as XSMT, FLT, DEMP, and FMT is it required that I place a resistor between the pin and the GND / +3.3v? I've assembled a test board and it's not functional, so I'm trying to rule out the fact that I have my pins driven directly from 3.3v/GND as the culprit.

Thanks,

-Ted

  • Hi Ted,

    It is not required - though it can be convenient to have unpopulated resistors to both GND and +3.3V, then only populate one. That way you can modify the configuration later.

    For the PCM5102A there are a few common issues to check:
    1. Is the I2S input valid? If using 4-wire mode, the clock configuration must be on table 10 on the datasheet and not denoted with '_(2)'. If using 3 wire mode, the clock configuration must be on table 11.
    2. If you have a valid clock, what is is the voltage on VNEG? Are you using a 2.2uF on charge pump pins?
    3. Do you have a load on the DAC output?

    Thanks,
    Paul
  • In reply to Paul_Frost:

    Hi Paul,

    Thanks for the response!

    1. I'm using 3 wire mode, though I did neglect to ground the SCK pin in my design. I've added a jumper wire to GND from this pin in the meantime. I'm unable to verify the validity of the I2S coming in because I don't currently have access to a scope (though I can get access to one if need be). I have tested this setup using a cheap "Raspberry Pi Hat" PCM5102A build and everything worked fine.

    2. I'm pretty sure I have a valid clock because I do see the VNEG pin jump to -3.25v when I2S is active and 0 a few seconds after the line goes idle. I am indeed using 2.2uF caps on the charge pump pins. Is there a good way to tell if the input I2S is valid without a scope?

    3. There's a pair of earbuds on the DAC output. I'm seeing ~10mV before and after the output resistors and caps regardless of anything being plugged in.

    It may be worth mentioning that my design pulls FLT, FMT and XSMT up to 3.3v and the input data is left-justified @ 44100 khz.

    Thanks!

    -Ted

  • In reply to Theodore Salmon:

    Hi Ted,

    I think the problem here is that your are using earbuds. The PCM5102A is not a headphone driver. It may be surprising, but headphones are actually have hard load to drive. Most are between 8 and 32ohms. If you look at the PCM5102A datasheet, you will see that the minimum output load impedance is 1kohm! The PCM5102A is designed for line-out only, with the user adding there own amplifier to drive their headphones or speakers.

    You should try looking at the output with an oscilloscope to see if the DAC is working, or connect the output to amplifier (or receiver).

    Thanks,
    Paul
  • In reply to Paul_Frost:

    Pete,

    While the PCM5102A isn't suited for driving earbuds, it does work :).

    I soldered up one of my PCM5102AQ1's to the cheap breakout board I mentioned earlier and I'm getting good audio out of the earbuds now. My assumption is that I have missed something fundamental in the schematic or layout.

    I'll update this thread once I figure out what's actually causing my issues :).

    Thanks again for your all help!

    -Ted

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.