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PCM4204 does not provide 2,5V on Vcom

Other Parts Discussed in Thread: PCM4204, PCM4104

Hi,


I'm using the PCM4204 in a costum board design. The input circuits are equal to those in the data sheet (Figure 16/17). The ADC is running and generates the right clock signals, but the output pins Vcom12 and Vcom34 do not provide the 2,5V like discribed in the data sheet.

Have you any idea what can cause this error?

best regards

Roland

  • Hi Ronald,

    Since this is on a custom board there are many variable that could effect this. I have a few questions to help identify the situation:
    What voltage is output on Vcom?
    Are you following figure 15 for the connections to Vcc, Vdd, and the Vref pins?
    Are your voltage rails correct and are the voltages you are supplying to the part meet the data sheet requirements?

    Justin
  • Hi Justin,

    On both Vcom12 and Vcom34 there is 0V.
    The supply connections are designed just as in figure 15.
    I'm using 5V for Vcc and 3.3V for digital curcuits.
    To be certain that the rails are correct I messured the voltage directly on every single supply pin.

    However, there are two diffrences between my schematic and figure 15.
    I'm not using these 100Ohm resistors for clock and data rails etc. (not sure if this is important)
    And only PCM format is used, so the pins DSDCLK, DSD1-DSD4 and SUB are left unconnected.
    The pins TEST and EPAD are unconnected too.
  • Hi Roland,

    Please gnd the test pin as suggested in the data sheet layout and done in the EVM layout.

    Justin
  • Hi Justin,
    it's very difficult to reach the pins, so I can't try to do so. I didn't connect it because of its internal pull down resister.

    But I had another idea while reading in the data sheet of PCM4104 digital-analog-converter. This DAC is also included in my design and this IC has 2.5V pins too. So I took the necessary voltage of those pins.

    Not a very smart solution but it works.
    Thanks for your efforts
  • Hi Roland,

    Could you show me your schematic for the Vcom and Vref pins? If the part is working correctly you should have 2.5 V on the Vcom pins.

    Justin
  • Hi Roland,

    Did you ever figure out why VCOM was not working. I am having the same problem.

    I have four development boards with 2 PCM4204's on each one. One board is working, 3 are not.

    The batch code on my parts is 36C7TFT. Could you check the batch code on your parts?

    Thanks,

    Gerry
  • Hi Gerry,

    I did not figure out why it isn't working. But I'm working on a new design wich will include a new ordered PCM4204. This might take a week or two to get the board ready.
    But that is very strange that it isn't working on a development board. Perhaps there are no faults of mine and in this case I just hope for the best.
    The Code on my IC is 17A38TT.

    regards,
    Roland