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PCM3168a not operating

Jack Dagdagan
Prodigy 120 points
Other Parts Discussed in Thread: PCM3168A

Hi,

I want to use the PCM3168a in slave mode to convert some MEMS microphone signals to I2S streams. I have connected the USBStreamer by the company miniDSP to SCKL,BCKAD,LRCKAD and DOUT1. The MEMS microphone is attached to VIN1+ and VIN1- via the interface circuit from Figure 58. I have buffered the supply ports as recommended in Figure 54. Mode is connected to ground. Unused analog inputs are connected to ground. DIN1…DIN4, RST, OVF, Zero, MC, MS, LRCKDA, BCKDA, MDI, MDO, VOUT1…VOUT8, DOUT2, DOUT3 are not connected.

VCC  to GND is 5V, VDD is supplied by a 3.3V voltage regulator.

I don't get any signal out of the PCM3168a. It does never get warm when I apply the supply voltage. What am I doing wrong?

Thanks a lot!

Jack

  • 0
    Prodigy 120 points

    I tried to debug the issue by measuring the pin voltages. Is it possible that I need to keep RST high the whole time in order to keep the codec running? I would really appreciate an example of a minimal application around the PCM3168a. I thought that I do not need any control pins if I operate the device under default the settings.

    Thank you!

    Jack

  • 0 in reply to Jack Dagdagan
    TI__Mastermind 27900 points
    Hi Jack,

    Yes reset must be held hi or low and cannot be left floating. Are you controlling the PCM3168A in HW mode or software mode?

    Justin
  • 0
    Prodigy 120 points

    Ok, I am holding RST at VDD=3.3V now and I finally get some output. The problem now is that it is the wrong output. the microphone signal is totally lost, I only get some impulse every 10ms. I attached a picture of the signal plot.

    I thought maybe this is some clock related issue? The device is running in slave mode. I don't write to the register settings, so everything should be running in default settings. Sampling frequency Fs is 96kHz, BCKAD is 64xFs, System Clock is 256xFs.

  • 0 in reply to Justin Bohr
    Prodigy 120 points
    Thank you for your answer Justin,
    Please read my last reply. I am controlling the PCM3168A in software mode (I2C), but the control pins are floating, because I thought I can operate everything in default mode (differential input signals, etc.)
  • 0
    Prodigy 120 points

    Please give me some support, I am very certain that the problem is trivial for an expert. What do I need to consider?

  • 0
    Prodigy 120 points

    I took a picture of the I2S signal. It looks as if there are 16 bits data and 16 bits zeros only. But I have checked the clocks and SCKI/LRCKAD is 256 and BCKAD/LRCKAD is 64. What is causing this?

  • 0
    Prodigy 120 points
    I found out that the the i2s stream is not always 16 bits {0,1} but rather periodically 24 bits {0,1}. Those samples that have 16 bits {0,1} have {0} for the higher bits. Those with 24 bits have {0,1} for the higher bits. So the issue definitely has something to do with the circuit around the codec. Does anybody know what kind of errors in the wiring of the chip can have such an effect? Can this be due to unstable voltages?
  • 0 in reply to Jack Dagdagan
    TI__Mastermind 27900 points
    Hi Jack,

    Is it possible for you to post a schematic of the connections you have to the part, and then you said you are using default register definitions, as in you are not driving the I2C lines at all?

    Justin
  • 0 in reply to Justin Bohr
    Prodigy 120 points

    Hi Justin,

    Thank you for the reply. I have attached a screenshot from my eagle schematic file. To the left I have connected the microphones via the amplifier circuits as mentioned earlier in this thread. I don't drive any I2C lines at all. Do I need to transmit any I2C signals if I just want to use the codec in default modes?

    Thank you!

    Jack

     

  • 0
    Prodigy 120 points

    I managed to get some sound recorded using the codec now. I have attached two 96 kHz wav files, one the original recording from the codec, the other one a clipped version. Due to the advice from Luis Fernando I am now certain that that nuisance noise comes from DGND and AGND being connected to the same ground plane. It would be nice if you could listen to the recordings and see whether you can argue against my suspicions.

    Thank you!

    Jack