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PCM1864: Using multiple I2S audio DACs with the same clock

Jejomar Ildefonso
Genius 9490 points
Part Number: PCM1864
Other Parts Discussed in Thread: TMUX1308, PCM1860, TMUX1309

Hi Team,

You've helped us to put on our customer to decide on PCM1864 as it takes 4 analog stereo audio and outputs 2 independent digital I2S audio. They saw that it uses the same WS and CLK signals for both channels despite being fully independent from each other. However, they've come across a few follow-up questions:

Can I use other I2S audio devices with their DOUT signal while using my WS and CLK from PCM1864? Or should they have their own independent CLK and WS lines... assuming all 192khz?

My real world case is an HDMI transmitter IC which can have multiple I2S audio inputs but has only one CLK and one WS inputs... and I have different sources of audio in my board... analog audio to converter by PCM1864, and also separate digital I2S audio coming from HDMI receiver ICs and external connectors.

Can I take CLK and WS from PCM1864, and just take the DOUT from all these sources? Or should they be with their own independent CLK and WS?

If they should have their separate independent CLK and WS, then I thought of using 3 TMUX1308 to choose select the desired input... one TMUX1308 to pick the required I2S DOUT signal, one for WS, and one for CLK.

Please advise for this issue + if separate signals are required, will the TMUX1308 be a good apprach? Is TMUX1308 suitable for audio signals here?


Thanks in advance!


Kind Regards,

Jejomar

  • +1
    TI__Genius 13610 points

    Hello Jejomar,

    Could you clarify a couple of things:

    Are PCM 1864 being used as slaves or masters?

    What are you referring to as WS?

    If you have common devices needing same clock with only one source of that clock it should be fine as long as you keep in mind possible situations where for some reason a device would produce noise on that clock signal which is not likely but not impossible but also depends on capacitance and layout of board if everything is close together with min capacitance it would seem to be okay but you don't want numerous long traces that would increase capacitance to point where there is phase shift or distortion in clock depending on where you take a probe.

    Also for the idea of buffering to isolate the clks see this brochure for ideas and part examples:

    www.ti.com/.../slab060.pdf

  • 0 in reply to Carson Allen
    Intellectual 360 points

    Hello,


    I am the original poster of this question.


    I decided to use PCM1860 since it is significantly cheaper, but the question stands for PCM1864 as well.


    I don't know about master or slave to be honest. However, here are the audio sources that I have:


    1- Source 1: I have 3 analog audio inputs, all go to PCM IC and it outputs I2S signals DOUT, BCLK, LRCLK.

    2- Source 2: I also have another IC which takes HDMI video and delivers parallel video bits (60 bits) + audio as I2S output.

    3- Source 3: external I2S input from a PCM1860 which is outside the device itself. So the device will have only the 3 I2S signals.

    4- Source 4: same as source 3.


    All of them will go to 2 HDMI transmitter ICs which has up to 6 I2S inputs. However, the HDMI IC has one BCLK and one LRCLK inputs, but has 6 DOUT inputs. Therefore, I need to route all 3 signals from each source when I choose it. I thought of why not just use one BCLK and one LRCLK from one of the sources for all sources and just route the DOUT... will it work? I figured this since they are just clock and word select.... all sources are 192khz too.


    If this won't work then I got TMUX1309 to switch all 3 signals for all 4 sources... all TMUX1309 ICs take inputs without buffering. please check the attached image for schematic.



    please check and get back to me if this works.







    Here is the attached image: https://imgur.com/a/aCBsuRq

    best regards

  • 0 in reply to Hossam Moghrabi
    TI__Genius 13610 points

    Hello 

    Could you please copy and paste into new post and I will reply there. It helps keep our forum organized.

    Best Regards,

    Carson