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  • TI Thinks Resolved

ISO7762: to replace ISO1541 and ISO7731

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Replies: 5

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Part Number: ISO7762

This design guide (http://www.ti.com/tool/TIDA-050026-23881) recommends ISO1541DR for I2C and ISO7731DWR for Reset, INT and OSS. Can I use ISO7762DWR which has 6 channels to do the job of both parts?

Thanks,
Nick

  • Hi Nicholas,

    ISO1541 is a bidirectional I2C isolator while ISO77xx is a unidirectional device where the direction for a given channel can be in either direction but will be fixed. While for ISO1541, the data can be transmitted in either direction at any point of time. Hence, ISO77xx cannot replace ISO1541 and I recommend you to use both ISO1541 and ISO7731 to meet your application requirement. Thanks.

    Regards,
    Koteshwar Rao

  • In reply to Koteshwar Rao:

    A schottky diode solves the problem with needing to be bidirectional since you have separate SDAI and SDAO pins. Actually some of your competitors recommend similar unidirectional isolator parts for I2C by using an external schottky diode as in the attached schematic below. I could do the same using ISO7762DWR.

  • In reply to Ufuk Karaaslan:

    Hi Ufuk,

    Thank you for sharing additional inputs relating to your requirement. I agree that the above approach can be followed to achieve bidirectional function provided the I2C node (mostly MCU) that is connecting to the isolator has SDA_IN and SDA_OUT available separately as unidirectional channels. If this is the case then yes, you could use a Schottky diode on the bidirectional side (or bus side) to be able to use unidirectional digital isolator.

    I also see that the SCL channel is unidirectional, I am assuming you do not require clock stretching feature in which case unidirectional clock is okay.

    Please do confirm if the assumptions I have made about your application requirement are correct. If yes, then you can use ISO77xx and meet your requirement. Thanks.

    Regards,
    Koteshwar Rao

  • In reply to Koteshwar Rao:

    Hi Koteshwar,

    As long as the master (host processor) keeps the clock rate under 400kHz, clock stretching should not be needed by TPS23881 or TPS23882, correct? Actually I see that the TI EVM Users Guide (slvubq3 page 18) for TPS23882 utilizes a similar isolator (ISO7241) for SCL.  So I think we should be fine.

    Thanks,

    Ufuk

  • In reply to Ufuk Karaaslan:

    Hi Ufuk,
    Thanks for the confirmation. Looks like you are good to use the ISO7762. Thanks for reaching out to us in clearing out your doubts.

    Hi Nick,
    I am not familiar with TPS23881/2, if any further clarifications needs on those devices please reach out to the respective team/forum. Thanks.

    Regards,
    Koteshwar Rao

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