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ISO1540: Can I parallel ISO1540?

David Chance
Genius 4760 points
Part Number: ISO1540
Other Parts Discussed in Thread: ISO1541,

Can I parallel multiple ISO1540s to use one I2C bus to talk to multiple isolated I2C slaves with different address? I assume so, but would like to confirm it before placing it in my design

Thanks!

  • 0
    TI__Expert 6195 points

    Hi David,

    Thanks for asking your question on E2E and for providing a quick sketch. 

    In short, yes this is fine. For more details please see this E2E thread. 

    Please let me know if you have any additional questions!

    Best regards, 

    Dan

  • 0 in reply to Dan Kisling
    Genius 4760 points
    Thanks, and I followed your link to see the other thread, the diagram in the other thread seems to have the wrong usage on the isolator? I think the single master should be the one sends out the clock to multiple slaves, so the direction of SCL is wrong. If ISO1541 is indeed used like the schematic, side 1 should be the input side, side 2 should be the output side, meaning side 1 should be in the bus side, while side 2 in the device side.

    Could you take another look at that and clarify it?
  • 0 in reply to David Chance
    TI__Expert 6195 points
    Hi David,
    Thanks for catching that. Yes, the direction of SCL does look incorrect. Let me check this with our resident I2C expert on Monday to make sure that I provide you with the best information. Sorry for the inconvenience.
    Best regards,
    Dan
  • 0 in reply to Dan Kisling
    TI__Expert 6195 points
    Hi David,
    Again thanks for pointing out the mistake in our previous post. I've checked in with our resident isolated I2C expert and they confirmed that the drawing was incorrect in the previous post. Please see the following notes.

    1. Side1 always needs to connect to MCU (master/slave) and Side2 to bus.
    2. Slave SCL should be input only, hence ISO1541 can’t be used for slave.
    3. For Slave SCL to work, only ISO1540 should be used.
    4. Only Master can use ISO1541. If it requires clock stretching then it should use ISO1540 only.

    Please let me know if this clarifies the requirement better.
    Thanks and best regards,
    Dan