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Original question:

Help to define the best reference design for IOT Gateway development

Isolated Digital Input and Output Interface

Guilherme Augusto
Prodigy 170 points
Other Parts Discussed in Thread: ISO7741, SN6501, ISO1211

Hello,

i'm developing an IIOT Gateway using some design references from TI. I made a block diagram and I'd like to know if it's correct and reliable in terms of isolation 

Thanks

  • 0
    TI__Genius 17100 points

    Hi Guilherme,

    Thank you for posting to E2E! From this schematic the digital isolator looks to be configured correctly. Please ensure the power supplies on both sides (Vcc1 and Vcc2) are within its datasheet Recommended Supply Voltage range.

    The ISO77xx family of devices can be used for this project: ISO7741 as an example. To help recommend a part, how many data channels are needed? How many of those channels are inputs and outputs to the Raspberry Pi / MCU?

    For your consideration, an SN6501 or SN6505 circuit can also be used to generate an isolated 5V supply directly from the 5V rail on the field side. Let me know if you would like more information on this.


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 30 points

    Dear Manuel, thank you very much for your advice.

    I also participate in this development. Your recommendation about using the SN6505 is very useful, but we have a small inconvenience that is the maximum electrical output current is 1A. There is a possibility to add some configuration or other chip that allows me to have between 2A and 2.5A.

    Best regards.

  • 0 in reply to ever quinones
    TI__Genius 17100 points

    Hi Ever,

    You're welcome! I understand the SN6505's current capability is a limit here. If you'd like to evaluate it in future projects, please feel free to reach out.

    When creating the isolation schematic and PCB for this Gateway IIoT, ensure GND and power connections or planes on the field and MCU sides are separated. In schematics this is typically achieved by using separate net names for each local GND and power connection, and in PCB layout there is a visible separation between copper on the two sides. TI can also review those on this thread if you'd like or directly via E2E's Personal Messages.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points

    Hi Ever, Guilherme,

    Just a note, it's also possible to isolate the Field I/Os directly using ISO1211 or ISO1211 if you prefer to have digital inputs isolated independently from the serializer so that any serializer failures affect only the serializer channel(s).

    Additionally, I'd like to suggest the ISO7741 to use for digital signal isolation since it has a proper channel configuration for SPI communications (3 forward for CLK, /CS, MOSI and 1 reverse for MISO).


    Please let me know your thoughts or any questions.


    Thank you,
    Manuel Chavez