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Original question:

PCM1681: Customer wants to combined use LRCK for DSD compatible model

PCM1681: How should user use PCM1681 in order to avoid the hung by unexpected DSD data input

Koki Tsushima
Prodigy 695 points
Part Number: PCM1681

Hi expert, 

I want to ask three questions for PCM1681.

Q1

How should be un-used pin for DATA1-4? Is it OK to be Open or needs to be connected to pull-down resistors? If the later, could you tell me the recommended values of pull-down resistor?

Q2

Let me confirm to make sure when the case which Glitch noise (=short pulse than normal "high" signal) is input to SCK/ BCK /LRCK.

For that time, will not be hung if Glitch noise for 1 pulse is input to them when SCK/ BCK /LRCK was inputted or loss? 

I personally think this is yes, by refer to former E2E by me

(https://e2e.ti.com/support/audio-group/audio/f/audio-forum/1048809/pcm1681-customer-wants-to-combined-use-lrck-for-dsd-compatible-model?tisearch=e2e-sitesearch&keymatch=PCM1681%20tsushima# ),

If an unexpected DSD data signal is sent to LRCK, no damage will be resulted, because as far as the pin is concerned, just  a "wrong" signal  is sent to it and  therefore the part  should not function.

Is this understanding correct?

Q3

Let me confirm to make sure when DSD data may be also input.

By refer to https://e2e.ti.com/support/audio-group/audio/f/audio-forum/1048809/pcm1681-customer-wants-to-combined-use-lrck-for-dsd-compatible-model?tisearch=e2e-sitesearch&keymatch=PCM1681%20tsushima#,

it may be hung for worst scenario if DSD data was inputted to LRCK of PCM1681.

Therefore, customer try to keep "L" for LRCK when DSD audio was played by changing their circuit.

Is this solution a good way to solve the hung for worst scenario?

Customer think that there are no issue if DSD data was inputted to SCK/BCK because the frequency for DSD and PCM are same (i.e. DSD 2.8M　→ 22.57MHz/2.82Mz).

If this is true, though there is DSD data for DATA pin, but goes into suspend and the data will be ignored, then the music will be played again when all CLK was correct and synchronized.

Are those thinking true?

Best regards,

Koki Tsushima

  • 0
    TI__Mastermind 19290 points

    Hello Koki-san,  the I2S signals can be left floating , if not being used.

    Regarding your other questions, as it was mentioned in previous post, since this DAC is not really a DSD DAC, customer should not  use it  for that,  but if they just want to use it regardless , then it is their choice.   Although PCM1681 has fs of 192kHz ,compared to much faster fs of DSD systems,   I don't think the part will be damaged and probably their thinking might work for what they are saying, but honestly  I can not be sure of third question.  

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    TI__Prodigy 695 points

    Hello Arash-san,

    Thank you for responding again.

    Let me talk about the background again.

    I. Customer wanted to share the I2S signal line for PCM and DSD for their product.

    Estimated DSD is 2.8MHz to 11.2MHz and put into LRCK.

    II. We answered PCM1681 will not be functioned for that time because it was regarded "wrong" signal and will not be broken the device. 

       But for worst scenario, PCM1681 may be hung which needs power off, but the other DAC for DSD will be performed as usual, therefore, system will not be multifunction.

    For that background, I asked question 1, 2, 3 and 1 was closed. Let me discuss again for 2 and 3.

    2. Is it OK to tell as follows? If not, could you fix the sentences?

    When 1 pulse Glitch noise (=short pulse than normal "high" signal) is input or loss to SCK/ BCK /LRCK, we estimate PCM1681 will not be hung because it is configured just  a "wrong" signal.

    3. Is it OK to tell as follows? If not, could you fix the sentences?

    PCM1681 will ignore the SCK/ BCK of DSD , therefore, if SCK/ BCK of DSD will be inputted to DATA pin of PCM1681 data and LRCK of DSD will not be inputted to DATA pin of PCM1681 (by stay Low"), we estimate that the music will be played again when all CLK was correct and synchronized.

    However, note that PCM1681 is the device just for PCM, therefore, please confirm whether it come true or not on real situation. 

    Best Regards,

    Koki Tsushima

  • +1 in reply to Koki Tsushima
    TI__Mastermind 19290 points

    Hello Koki-san,

    Considering we have not done this in real life before, in theory probably it will be a wrong signal and will not work for PCM1681 but probably your answer is the best we can give them under these circumstances.

    Regards,

    Arash