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PCM2706 strange sound

Lucifer
Expert 2600 points
Other Parts Discussed in Thread: PCM2706

Dear Sir

We uses PCM2706 Audio DAC for USB MP3 player.

So far we encountered a problem need your help to clarify. below is our schematic file

http://www.seawalk.com.tw/0000/2.html 

When we turn on the system power,  PCM2706 has strange sound, we checked the waveform and found some strange as below video.

www.seawalk.com.tw/.../2.1.mp4

the situation only happens in the beginning 5 minutes of turning on power, then it will disappear

Moreover we ran EVT 500kits only 18kits has this issue.

May you give me some suggestion of this problem? Thanks,

  • 0
    TI__Guru* 95145 points
    Hi Passerby,

    Your schematic seems to be fine.
    I have viewed the video you shared, it seems that the signal is gone and then it comes back, but the transition is almost immediate.
    I think the problem could be on the digital section of the system. As the signal is abruptly interrupted there is a chance that a data packet from the USB host is lost or corrupted. Perhaps there is some kind of problem with the clock signals or the digital pairing.
    The crystal resonator circuitry is connected close to the PCM2706?
    VDD (Pin 21) is output from the internal voltage regulator, there is not an external supply voltage at VCC_3V3, right?

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Expert 2600 points

    Dear Sir,

    thanks for your reply.

    (1) Yes, the crystal is connected close to the PCM2706.

    (2) VDD(Pin21) we have used a buck 3.3v connect to this pin (VCC_3V3). is this a problem?

    Thanks.

  • 0 in reply to Lucifer
    TI__Guru* 95145 points
    Passerby,

    PCM2706 in BUS-powered internally generate its 3.3V supply rails from the 5V Vbus. So there is no need to connect an external supply voltage to VDD, VCCL, VCCR and VCCP. Although I don't think this is really the cause of the noise problem.
    Is there a way you could inspect the digital USB input signal to be sure that the signal reaches completely and not distorted to the PCM2706?

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Expert 2600 points
    Dear Ivan,
    That is digital USB input signal , I can not inspect it . Do you have any other suggestion for this issue? Thanks.
  • 0 in reply to Lucifer
    Expert 2600 points
    Dear Sir,
    Any suggestion would be highly appreciated, Thanks.
  • 0 in reply to Lucifer
    TI__Guru* 95145 points
    Passerby,

    Sorry for the delayed response.
    I think the problem must be on the digital side, some kind of synchronization issue as this seems to be solved after 5 minutes.
    Could you please share the layout? This is just to take a look how is it all connected. You can send it to my mail address ivan.salazar@ti.com if you don't want to upload it to the forum.
    The video you uploaded shows a 1-kHz signal where a full cycle of the signal is missing.
    Is this behavior the same for any signal frequency? What I mean is, if you use a higher/lower frequency, is it missing a full cycle of the signal, too?

    Best regards,
    -Ivan Salazar
    Texas Instruments