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Original question:

ISO7742: Step in the middle of edge problem

ISO7742: How to do FSI isolation between two C2K MCU?

Dylan You
Intellectual 2630 points
Part Number: ISO7742
Other Parts Discussed in Thread: ISO7720, ISO1640,

Dear Teams,

My customer is using ISO7742DWR. They have two I2C interface (I2C_DATA and I2C_SCL) and two other pin (Power good and AC drop), which will be used for FSI to communication between primary side MCU and secondary side MCU. Could you help me check their schematic diagram and isolation table are correct or not?

 

TI propose

Isolation direction (TI)

I2C_PRIDATA

GPIO32 --> I2CA_SDA and FSIRXA_D0

Primary to secondary

I2C_PRICLK

GPIO33 --> I2CA_SCL and FSIRXA_CLK

Primary to secondary

PFC PG-A

GPIO10 --> FSITXA_CLK

Secondary to Primary

AC Drop-A

GPIO9 --> FSITXA_D0

Secondary to Primary

Thanks!

Dylan

  • 0
    TI__Guru 54245 points

    Hi Dylan,

    Thanks for sharing the schematic.

    I2C is a an open collector / drain bidirectional communication interface. If customer needs to isolate I2C interface then ideally they should use I2C isolator ISO1640 which is compatible to most I2C devices and provides isolation. For any additional unidirectional channels, you can use devices from ISO77xx family like the ISO7720 in this case.

    In your description, you have indicated the direction of communication. If these directions of data transmission are going to be maintained even thought this is I2C then unidirectional isolator channels can be used to transmit data as well. ISO7742 can definitely support such unidirectional channel isolation.

    Hence, please do check with customer regarding bidirectional / unidirectional channel requirement and accordingly suggest them to use either ISO1640 + ISO7720 or just the ISO7742. Let me know if you have any questions, thank you.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Intellectual 2630 points

    Hi Koteshwar,

    Thanks a lot for your help!

    The case is: I am pushing customer used FSI with these four pin (I2C_PRIDATA/I2C_PRICLK/PFC_PG-A/AC_DROP-A). If customer wants to change the I2C_PRIDATA and I2C_PRICLK pin to I2C interface, then we are not able to use existing schematic diagram with ISO7742 for bidirectional transmission, right?

    If customer wants to use FSI for these four pin, my schematic diagram is correct or not?

    Thanks!

    Dylan

  • 0 in reply to Dylan You
    TI__Genius 17100 points

    Hi Dylan,

    Yes, answering your questions, if our customer will keep the directions of data transmission mentioned in your original post, then unidirectional isolator channels of ISO7742 can be used to transmit data.

    A change in schematic to ISO1640 + ISO7720 will be necessary if our customer would like to implement bidirectional I2C communication.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Intellectual 2630 points

    Hi Koteshwar,

    Thanks a lot for your help!

    Dylan