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.

PCM1808: Pop noise

Part Number: PCM1808
Other Parts Discussed in Thread: PCM5100A,

Dear Sir 

Our system structure as below ,PCM5100A light channel have pop noise 

1. When we change a new PCM1808 ,this issue will be disappear

2. When we use probe or hand to touch LRCK of PCM1808 ,this issue will be disappear 

Do you have any experience of this issue? (schematic as below PDF file)

LOCAL V0.pdf

  • Hi, Kai,

    Thanks for he detailed information. This is not a common issue, the PCM1808 shouldn't have this behavior.

    From your comments, I could think that a solder problem could be the cause, maybe a unstable contact on the I²S clocks after the PCM1808. Did you tried using the PCM1808 with the issue in a different board?.

    Can you please share scope captures of the I²S signals at the output of the PCM1808 and at the input of the PCM5100A at the moment of the issue?.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • Dear Diego 

    1. We find some of date code PCM1808 doesn't have this issue 

    2. Due to input cap is 22uF ,do you have any suggestion?

    3. Do you have I2S layout guide?

    We need to spend a little time to measure the waveform ,could you help to reply above question ?

    Thanks 

  • Dear Diego

    Here is some feedback from customer:

    •It seems there is a resistor array before the input cap, it makes me think that the input signal that connects to J12 [SPK?] is conditioned to make it compatible with the input levels of the ADC (3Vpp for 0dBFS). Can you please confirm his?. Also, can you please check for the input value that is being conditioned.
    >> This issue is happened without any input signal
    •Regarding the input capacitor, the cutoff frequency is about 0.12Hz, usually 1µF is recommended instead.
    >> Customer will verify 1uF cap

    Do you know if customer has captures of the input signal at the moment of the failure?
    Any capture of the output stage after the PCM5100A could be useful as well.
    >> Customer use PCM1808 (TPA5052EVM) and jump the wire to their PCBA ,this issue will not happen again

    From the additional information posted by customer, I think that the issue could be related to an unstable connection on the board I²S clocks (particularly LRCK), do you know if they tried the suspect PCM1808 in a different board?. The noise could be caused by a clock mismatch, it would be good to have a capture of the clocks at the output of PCM1808 and input of the PCM5100A when the issue occurs.
    >> Customer will check the waveform and get back to you later.

    Thanks for your support.

  • Hi, Kai and Jefferey,

    Thanks for the feedback. Could you please clarify if the problem could be replicated in a different board with the device that showed the issue?. The 1µF capacitor is what we recommend, please let me know if changing it makes any difference. In general, there is no specific I²S layout requirement, if possible, pouring GND between the traces would be good.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • HI Diego

    We find all of fail device need to add damping resistor 100ohm on LRCK pin can solve this pop noise issue 

    1. Different date code device have different condition ,only one date code solution need to add damping resister 

    2. May I know why EVM have damping resistor ? have any history ??

    If anything or any data you need us to provide to you ,please kindly let me know  

  • Hi, Kai,

    Thanks for the feedback. In general, the addition fo the resistors is done to enhance the integrity of the traces, this technique is used then the I²S traces are being routed a long distance across the layout or are interconnected through different boards.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • HI Diego

    I am appreciate your reply quickly
    1. Do you have any document to describe this long distance or interconnected through different boards
    2. Due to our customer test 33~75ohm resistor ,but the result is failed ,this issue can be solved when using 100ohm ,do you have any document to explain it ??

    Thanks
  • HI, Kai,

    Unfortunately, we don't have a specific document that could be useful for this class of applications. Let me check with our team if we have something that could point to the root of the issue, I'll contact you back if I get any feedback.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • Hi Diego

    Thanks for your reply 

    I am looking forward your good news 

    Thanks

  • Hi Diego

    Have any good news about this case 

    Seems like 100ohm can solve this issue ,but can't 100% make sure this is root cause 

    Do you have any idea how to explain this issue ? or something we can check ?

    Thanks