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PCM1789: During initialize the SPI port, there are noise at the output pins, cause unwanted voice at speaker side.

Xu Derek
Prodigy 10 points
Part Number: PCM1789

Tool/software:

If the mute pin is used, the noise at output pin will disappear during SPI initialization, but in our application, the mute pin is not used.

I would like to know, is it an inherent problem with the chip itself or somewhere wrong? and how to solve it in our application ( mute pin is not used).

  • 0
    TI__Mastermind 22720 points

    Hello,

    In general SPI or I2C activity should not be reflected at the output of a device.  Having said that , check "Mode control register reset"  MRST in register 0h10.  Datasheet  mentions  this bit sets the mode control register reset to the default value. Pop noise may be generated. You might not have any choice but using MUTE if this is the cause.

    Also it mentions that "During undefined data periods, some noise may be generated in the audio signal. Also, the transition of normal to undefined data and undefined (or zero) data to normal data creates a discontinuity of data on the analog outputs, which may then generate some noise in the audio signal." 

    In many of our DACs we  use the Mute to mask the pop noise that might be resulted from other sources such as interruption of clks or powering up the IC and you might not have any choice.

    If you still think this is not related to the above mentioned points, you can provide more insight to this issue by considering the following:

    1) Do you mean there is no noise at the output, until the SPI communication takes place and once SPI communication is done, the noise disappears as well?  That is,  any communication using SPI creates noise at the output? ( exclude the MRST bit that was mentioned above) 

    2) Do you see the same issue if you use I2C instead of SPI? If it is because of the register 0h10, you still would see it, if not , then probaly it is related to  SPI itself.

    3) While you are writing via SPI, are you sending any input signal to the DAC as well? If yes, repeat it with no input signal- just to be sure.

    4) Please isolate the DAC from any other IC that you are sharing the SPI signals with it. 

    5) Are you sharing the power supplies? for example , is the same supply  connected to DAC and source of SPI, or any other IC sharing the supplies? Also refer to layout guidlines in datasheet for seperation of supplies even within the DAC itself.

    6) Are the SPI traces crossing the DAC outputs on the board such that it  might create unwanted coupling noise?

     If you still have an issue, please share the full schematics along with answers to the above so we take a look at it.

    Kind Regards,

    Arash