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Original question:

I2S multiplexer / switch

TS3A44159: I2S multiplexer / switch

John Heaton
Intellectual 550 points
Part Number: TS3A44159

I have read a couple of posts that indicate the TS3A44159 switch would be suitable as an I2S MUX. I used the part in my PCB and it turns out the BCLK input switch is crosstalking. Obviously the BCLK is critical for timing in I2S when no MCLK is used.

I am using a 3.3V signal with single switch of the chip and BCLK1 being NC and BCLK2 NO,w/ output to a audio amp.

BCLK1 and BCLK2 are at different frequencies (different sources)

When in NC, (IN1-2 = low) there are no issues. Audio from BCLK1 is fine

When in NO, (IN1-2 =3.3V)  Audio from BCLK2 is being effected by BCLK1 (digital noise).

I verified this by cutting the trace of BCLK1 and noise was eliminated

Any suggestions on how to eliminate the crosstalk?

As an alternative, if I use two of the switches instead of 1, would the crosstalk remain?

example -

Switch 1 NC = BCLK1

Switch 1 NO -= OPEN

Switch 2 NO = BCLK2

Switch 2 NC = OPEN

So when IN1-2 is toggled, the source changes.

My concern is that if I leave one leg of the switch OPEN, it will create problems since your datasheet recommends 50ohm to GND. Obviously if I tie the open to GND it will kill the signal.

What do you recommend in this situation?

  • 0
    TI__Expert 3920 points

    Hi Jon,

    thank you fr reaching out to us.  Which frequencies are the I2S BCLK on? At around 48kHz there should be very low crosstalk (-70dB).

    Have you measured the crosstalk according to Figure 24 in the datasheet?

    If two devices would be used, the crosstalk would be an non-issue, but I think there could be another issue.

    Let us know how much crosstalk you see in your implementation.

    Thank you and best regards,

    Ambroise

  • 0 in reply to Ambroise Suter
    Intellectual 550 points

    Well the BCLK is a result of the following.. 

    44.1 kHz × 16 × 2 = 1.4112 MHz and can be as high as 48 kHz × 32 × 2 = 3.072 MHz

    Since I don't have a test setup (breakout board), doing this experiment on my finished PCB would be near impossible (6mil traces..), so I can't really answer that part of the response.

    In terms of using two devices, that's not what I was suggesting. I was suggesting using 2 of the 4 switches within a single TS3A44159 device. The idea being, instead of using the shared transistors within a single switch, using switch 1 for BCLK1 and another for BCLK2, as you can see in the picture below. I'm wondering if the crosstalk is a result of the shared transistors and therefore not using the same transistor path would help with the issue?

  • 0 in reply to John Heaton
    TI__Expert 3920 points

    Hi John,

    with 3Mhz, the crosstalk isolation is at -45dB. With a signal of 3.3V the crosstalk signal should be below 0.02V. That's why I think there could be another source.

    Your suggested solution should improve it anyway though, maybe even use NC1 and NO2 to maximize the distance of the BCLK traces on the board.

    Best regards,

    Ambroise