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iso72xx

luca turrini
Intellectual 300 points
Other Parts Discussed in Thread: ISO7221C, ISO7240M, ISO7242C

I'm designing a new project with two type of optocoupler: ISO7221C and ISO7240M.

Is is possible place the two components  in the same PCB position but one top and the other bottom or there are different PCB indication?

In the ISO7221C which is the maximum frequency for a clock signal ? 25MHz or 12.5Mhz?

Thank you

  • 0
    TI__Mastermind 21901 points

    Hi Luca,

    For your first question, are you just asking if you can have one isolator on the top layer of the board and another isolator on the bottom layer? Where both isolators would share the same isolation barrier?

    In terms of your second question, the 25MBPS is how many bits (edges) per second. Therefore with 25MBPS, you can have a 12.5 MHz square wave.

    Let me know if I am understanding your first question correctly and I can follow up.

    Thanks,

    John

  • 0 in reply to John Griffith
    Intellectual 300 points

    Hi John,

    you have understand corretly. Probably I will use an ISO7240M and ISO7242C on the same PCB point, where the VCC1 of the two optocoupler is the same (3.3V) and the Vcc2 also the same (5V).

    Do you think I could have any interference problem between the two chip?

    Thanks

    Luca

  • 0 in reply to luca turrini
    TI__Mastermind 21901 points

    Luca,

    I want to start with letting you know that our team has never tested a system like this before. Ultimately I believe the two devices will end up coupling some noise from each other, but I do not believe it will be to the extent where they interfere with communication. 

    Unfortunately, since we have no data that shows how much noise couples between two isolators installed on opposite sides of a PCB, I cannot guarantee this. My gut reaction is that FR4 is a good insulator, and I think that it should not be an issue.

    Thanks,

    John

  • 0 in reply to John Griffith
    Intellectual 300 points

    In the past I've had many problems with HS magnetic coupler form AD, placed on opposite sides of PCB.

    Do you have any indication about minimum distances of your components? This optocoupler works different for magnetic type (ADUM14xx)?

    Thanks

  • 0 in reply to luca turrini
    TI__Mastermind 21901 points

    Hi Luca,

    I do not know if we can compare the two in an apples to apples comparison. Analog Devices isolators use transformer based isolation. And as you can imagine the transformers on chip will create magnetic fields that are being used to inductively couple the two sides. I would imagine that this would cause much more of a noise / cross talk issue.

    The isolation technology from Texas Instruments is completely different. We use a capacitive isolation technology where a dielectric barrier is placed between the input and outputs creating the isolation barrier where no current needs to flow to pass a signal across the barrier. It is also known as galvanic isolation.

    I do not think we can compare the two technologies.

    Thanks,

    John