• State
  • Locked Locked
  • Replies 6 replies
  • Subscribers 30 subscribers
  • Views 652 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

PCM2704C

Mehrdad Bradaran
Intellectual 430 points
Other Parts Discussed in Thread: PCM2704C, TPA2008D2

Hello,

Can you please help with the following.  My customer has a new design with P/N: PCM2704C.  They have built 2 boards and tried on 2 different computers. When normal audio is played through their boards, it sounds good except for a periodic clicking sound about 5 times a second. Other commercial USB speakers
sound fine using same computers and audio sources.  To investigate furthers, they used the audio program "Audacity" to generate a pure sine wave tone of 4000 Hz. When played through their boards, the audio is reproduced cleanly except that about every 200 mSec the audio output goes to 0 for 1 mSec, then continues a clean tone.  They are using the schematic in the PCM2704C datasheet. There appears to be no drivers you can tweak on the PC side. They don't have an EEPROM on the PCB2704C, but that seems to be optional.  I have attached the scope picture.  Please advise.PCM2704 scope pic.docx

  • 0
    Expert 1720 points
    It is really strange. I never had troubles with PCM270x. Do you have more informations like schematics and PCB design? It is possible that your customer forget something or PCB design is not good. More frequently it is software or USB hub or cable problem.
  • 0 in reply to Pavel Ruzicka
    Intellectual 430 points

    Schematic and scope.pdfThanks, Pavel.  It is strange.  Attached please find the schematic for the design.

  • 0 in reply to Mehrdad Bradaran
    TI__Guru* 95175 points
    Hi Mehrdad,

    As Pavel said this is not commonly seen. Is this issue present on different boards?
    Perhaps the problem is related to the clock circuitry.
    I will take a look to your schematic.

    Best regards,
    Ivan Salazar
    Texas Instruments
  • 0 in reply to Mehrdad Bradaran
    TI__Guru* 95175 points
    Hi Mehrdad,

    I can see in your schematic that you have a TPA2008D2 integrated in your application.. It seems that you've configured PCM2704C in Bus-Powered 500mA, but there is a TPA2008D2 sharing this supply so maybe the USB power can't supply both devices.
    Have you tried to use only the PCM2704C without the TPA2008D2. Another option you can try is to use a different power supply for TPA2008D2.
    Let me know if you try any of the above.

    Best regards,
    Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Intellectual 430 points
    Hi Ivan,

    Yes, they have tried different power supplies, and also built a board with just the USB chip on it. On one experiment they added a big capacitor on the power leads. This is their reply:

    "I don't know that much about USB data transmission, but I think the basic packet takes 1 mSec. From what I saw, the dropout could be exactly 1 packet, so to me it sounds like a operating mode, or buffer allocation or driver problem. I was hoping a USB guy would recognize these symptoms as a known USB phenomenon."

    Please advise.

    Thanks,

    Mehrdad.
  • 0 in reply to Mehrdad Bradaran
    TI__Guru* 95175 points
    Hi Mehrdad,

    Indeed, each packet contains 1 mS of audio data. So it seems that it is losing one packet every 200 mS.
    Have you tried to modify your oscillator circuitry? Is this circuitry close to the PCM2704C?

    Best regards,
    Ivan Salazar
    Texas Instruments