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TAD5242: While inputting the TDM signal, an unexpected waveform appears on MD6.

Chia Tesng Chuang
Prodigy 50 points
Part Number: TAD5242

Tool/software:

Hi TI,

I am using TAD5242 to input TDM signals at DIN (channel = 4, Left Justified, MSB First, One Subframe, Word Width = 32, Bit Depth = 24, Falling Edge Sync, FS = 48kHz),

and observing MD6 with an oscilloscope.

I noticed an unusual signal and would like to understand what it is. Could it cause pop noise or other abnormal behavior?

  • 0
    TI__Mastermind 30671 points

    Hi Chia,

    The TAD5242  has daisy chain option for TDM mode of operation which is auto enabled whenever device is selected to be in TDM Mode. MD6 Pin acts as a Daisy Chain output in this mode. And  the device plays the audio present on the last 2 slots, and the remaining slots are shifted to the right and sent on the MD6 pin. ( see  Figure 6-2. Daisy Chain in TDM Mode Block Diagram) 

    So from your description, it is sending out the daisy chain output of the other 2 channels out to the next device . 

    Please  make sure your BCK comply with this equation :  BCLK= # of Ch.  *  Ch depth  * Fs

    Regarding the pop noise question, it should not show up as pop noise as it is part of the operation of the chip 

    Kind regards,

    Arash

  • 0 in reply to Arash Loloee
    Prodigy 50 points

    Hi Arash Loloee,

    Thank you for your reply~


    There are two points I'd like to confirm with you:

    1. My equation for BCLK is: channel number * Word Width * Fs
    Is this different from this equation? : BCLK= # of Ch. * Ch depth * Fs

    2. Regarding previous discussion, the red highlighted in the previous pictures is normal behavior, correct?

  • 0 in reply to Chia Tesng Chuang
    TI__Mastermind 30671 points

    Hi Chia,

    I think we are talking about the same parameters in the equations, so same equation.

    As I mentioned the MD6 pin is the output of Daisy chain from first DAC that will go to the second DAC. So for TDM4, the  data from the first 2 slots will be processed by the first DAC and the first DAC will pass along the data of the next 2 slots via MD6 to the DIN of the second DAC in the daisy chain. So  I don't see any issue with MD6 changing levels, but you have to monitor  it to make sure that the data that you see at this pin matches with the above statement.

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    TI__Genius 16130 points

    Hi Arash,

    Thank you for your information. Customer question here is that they are wonder if the pop noise during the LRCK state transition is normal or not.

    I saw that you answered was the operation of the chip. May you help describe more detailed? or do we show the information in datasheet/app note?

    Arash Loloee said:
    Regarding the pop noise question, it should not show up as pop noise as it is part of the operation of the chip 


    Regards,

    Roy

  • 0 in reply to Roy Chou1
    TI__Mastermind 30671 points

    Hello Roy,

    Lets rewind,  please identify the waveform in the plots, I believe you have BCK, LRCLK and the pink is input, is this correct? Is it the input to DAC2? Because you indicated 4 channel, and I see only 2 channels here , so I assume it is the data going from DAC1 to DAC2. And to comment we need to see the TDM4, signal ( all clks and inputs going to both DACs)

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    Prodigy 50 points

    Hi Arash,

    This is the the TDM signal you need.

    Regards,

    Gary

  • 0 in reply to Chia Tesng Chuang
    TI__Mastermind 30671 points

    Hi Gary,

    Thanks for the plot. I  think what you see has to do with selection of SHIFT LEFT on the AP selection of data generation/clks . But the pulse(s) that you show has no effect on the pop noise as it appears on the channel that is not active in the operation. 

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    Prodigy 50 points

    Hi Arash,

    Thank you for your explanation~

    I received the second EVK these days, and after testing, there is indeed no pop noise.

    I'm still curious that even if it appears at the end of TDM slot 4, will it have no effect?

    ​​I would like to know the reason~

    Regards,

    Gary

  • 0 in reply to Chia Tesng Chuang
    TI__Mastermind 30671 points

    Hello Gary,

    As I mentioned above it has no effect on the operation .The pulse you are showing  is  on MD6 and is going to the second DAC -at the position that the first DAC is active and getting its  input from TDM4.

    Regards,

    Arash