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I2C with ISO1540D and two PCA9600 bus buffer

Andreas Wenzel
Prodigy 20 points
Other Parts Discussed in Thread: ISO1540, TCA4311A

Is it possible to use the ISO1540D with a PCA9600 bus buffer (for longer bus range) at both sides? I tried this, also with pull-up's, but it does't work.

What's wrong?

Thanks and best regards!

A.

  • 0
    TI__Intellectual 2200 points

    Hi Andreas,

    Side 1 of ISO1540 has its receiver thresholds at ~0.6V. The minimum low threshold on side1 is 0.5V. That is, only if the input signal is below 0.5V will it be detected as a low. It seems the VOL for PCA9600 can be as high as 0.74V. The low level driven by PCA9600 will not be recognized as a low by side 1 of ISO1540. This may be the reason why this scheme is not working for you.

    Rgds,

    Anant

  • 0 in reply to Anant Kamath
    Prodigy 20 points

    Hi Anant!

    Thanks! It seems you are right. The 2nd side works well with the PCA9600, but not the 1st.

    Is there a idea to fix it easy, because the pcb is produced now? I'm afraid, to change the pull-ups isn't the best way...?

    Thanks

  • 0 in reply to Andreas Wenzel
    TI__Intellectual 2200 points

    Hi Andreas,

    Even with higher pull up resistors, the VOL from the PCA9600 will remain higher than the IIL of the ISO1540.

    I think you need something like the TCA4311A - but unfortunately the pinout is different from the PCA9600.

    The other question to ask is if you really need bus extension on both sides? We can discuss by email if you like: anantkamath@ti.com

    Rgds,

    Anant