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ISO7742: Could ISO7742 be used in I2C isolation?

Walsh
Intellectual 950 points
Part Number: ISO7742
Other Parts Discussed in Thread: ISO1540,

Hi,

May i use ISO7742 in bidirectional I2C isolation? to replace ISO1540. connect as below figure.

If could not apply? Why?

Thanks

Walsh 

  • 0
    TI__Guru 53855 points
    Hi Walsh,

    The answer to your question is NO, ISO7742 cannot be directly connected to function as a bidirectional device. If you do connect them like you described in the image, the device would get latched to a single state and stops responding. Let me explain how does this happen in steps as given below.

    1. Let's assume SDA1 is made LOW by an MCU, this would make INA to force OUTA to a LOW state.
    2. Since OUTA is connected back to the other associated input INC in the other direction, INC will also force OUTC to go LOW.
    3. OUTC is going to hold INA LOW even when SDA1 is changed to HIGH.
    4. This makes Channel A & C latched to LOW state and stop responding to any inputs at SDA1 or SDA2 as long as the device is powered.
    5. A power cycle can bring the device back to a normal state but it gets locked to LOW state when any of the inputs is applied with a LOW.
    6. Hence a ISO7742 cannot be directly converted to a bidirectional device.

    Bidirectional channels using unidirectional digital isolator can be created using a few external components. To know how to achieve this, please refer to the article titled "Designing an isolated I2C bus interface by using digital isolators" on www.ti.com. You can also download the article at the link below.

    www.ti.com/lit/an/slyt403/slyt403.pdf


    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    Intellectual 950 points
    Hi Koteshwar:

    Thank you very much! The reply is very detailed and helpful. My question is solved by the answer.

    Thanks,
    Walsh