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ISO1640: difference between I2C isolator device and Digital isolator

Ella KIM
Expert 3862 points
Part Number: ISO1640
Other Parts Discussed in Thread: ISO7721,

Hello,

I have a back-to-basic question. I wonder the basic difference between I2C isolator devices and Digital isolator devices. I'm comparing ISO1640 and ISO7721. ISO1640 is a bidirectional 2 channel device while ISO7721 is one forward/reverse channel each. Also it looks ISO7721 supports higher surge voltage capability.

Other than these kind of structural difference, I wonder the functional difference. I checked both devices has different data rate spec, but if the data rate condition meets, I believe ISO7721 can be also used on I2C bus, and ISO1640 can be also used on the normal signal lines. Then, what would be a benefit over ISO7721 when I use ISO1640 in I2C bus? What is a benefit over ISO1640 when I use ISO7721 for the normal signal line?

Thank you for your advice.

  • +1
    TI__Mastermind 49485 points

    Hi Ella,

    Thanks for reaching out.

    Functionally, there are many differences between an I2C I/O and a general purpose digital I/O. The digital isolator cannot be use in I2C application without additional channels or external components while an I2C isolator can be used for general purpose I/Os but with many limitations.

    Before we delve further into functional differences, I would like to discuss about the isolation inbuilt into these devices. The isolation channel formed inside the device using isolation capacitors is very similar with similar isolation performance with ISO7721 being slightly higher in performance. Both of these isolation ratings are considered large enough to be used for most isolation applications.

    Coming to functional differences, the major difference between ISO1640 and ISO7721 is that each channel in ISO1640 is a bidirectional channel where the same channel can transmit data in either direction. The individual channels in ISO7721 are unidirectional, although the direction of the two channels in ISO7721 are in opposite they can only transmit data in the one direction they are designed for.

    I2C I/Os need to be open-collector/drain, ISO1640 meets this requirement while ISO7721 doesn't. ISO1640 I/Os support much higher sinking current (35mA) and max capacitive load of 400pF while ISO7721 I/Os can only sink a max of 4mA with a typical load of 15pF. The reason ISO1640 supports higher loading is because they are connected to an I2C bus with multiple nodes on it while ISO7721 is usually connected to just one device on either side.

    Since I2C operates at much lower speeds, ISO1640 also supports only low datarates. While ISO1640 can certainly be used in unidirectional general purpose I/O applications but it will be very poorly positioned when compared to the high performance unidirectional device ISO7721.

    I hope the above highlights help you understand the differences between ISO1640 and ISO7721. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Expert 3862 points

    Koteshwar, 

    Many thanks to your kind explanation. It helps a lot.