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  • TI Thinks Resolved

ISO1540: ISO1540 multiple ISO Slave on SDA1, SCL1 side

Part Number: ISO1540

From the datasheet I recognize that multiple slave devices are applicable to ISO1541.

But is it also possible to connect any i2c slave device on SDA1, SCL1 side?

The datasheet says that the maxium load permissible on the inputline, SDA1 and SCL1, is lower than 40pF and on the outputlines , SDA2 and SCL2, is lower than 400pF.

I am not sure about each slave device has which capacitive loads, it seems to be better to ask before start testing.

If possible, I would like to connect i2c expander and LCD on SDA1 and SCL1 line.

Regards

  • Hello,

    Thank you for your question and interest in isolated I2C.

    Do you have a part number for the I2C expander and LCD in mind?

    Our isolated I2C expert is out of office at the moment, so I will check into this matter for you. Please allow me until Thursday, December 14 to respond.

    Best regards,
    Dan
  • In reply to Dan Kisling:

    Hello, thank you for your quick response.

    I2C Expander part number is Microchip MCP23017 16bit I/O expander.
    And I2C Controlled LCD is ZETTLER DISPLAYS AQM1602Y.

    I hope I2C master (micro processor) can handle a ISO1540 as one of these slave devices.

    Best regards,
    Masashi
  • In reply to user5195160:

    Hi Masashi,

    Could you provide a quick block diagram of what you are trying to do? I am not sure that I understand your application.

    Thanks,
    Dan
  • In reply to Dan Kisling:

    Masashi,

    I am sorry, I have been waiting for a response from you but now I see that you have uploaded a block diagram in the original post (presumably quite some time ago). My sincerest apologies. I will bring this to our isolated I2C expert and get a response to you on Tuesday.

    Thank you for your patience,

    Dan
  • In reply to Dan Kisling:

    Hello Masashi,

    Side1 of ISO154x is the master side and recommended to be connected to Master only whereas all the slaves should be connected on Side2 of ISO154x. I hope that answers your question, thank you.

    Regards,
    Koteshwar Rao
  • In reply to Koteshwar Rao:

    Hello Koteshwar,

    Thank you for your reply.

    But in my application if all the slaves are connected on Side2 of ISO154x, the power supply on Side2 is not able to provide enough power to all the devices.

    In that case, how do you think the following idea?

    Put another ISO154x (#2) to Side2 of ISO 154x (#1) and drive Side 2 of ISO154x (#2) by the power supply of master side.

    In terms of cost, it is not good solution. But this idea should satisfy your recommendation and my requirement at the same time.

    Regards,

    Masashi

  • In reply to user5195160:

    P.S.

    The above solution seems to be OK about ISO154x #1. But regarding ISO154x #2 may have the same problem.

    There are multiple I2C connections on Side1 of ISO 154x #2.

  • In reply to user5195160:

    Hello Masashi,

    Sorry, I missed to respond earlier to this post.

    Your understanding of ISO1540 #2 facing a similar problem is correct. The best way to address this is to increase power on Supply B. Alternatively you could use isolated power solution to get additional power to Supply B side using device like SNN6501 / SN6505. Please refer to the datasheet of SNN6501 / SN6505 for more details.


    Regards,
    Koteshwar Rao

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