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F28069-ISO CONTROL CARD --> USB ISOLATION IN SCHEMATIC

Varaprasad Malisetty
Intellectual 460 points

Hi,

      I am trying to understand the schematic of F28069 ISO CONTROL CARD, up to page 3 it was understandable but on page 4 the ground used was the actual system ground used in page 3 and microcontoller GPIOs has been given directly to the USB connector. This will make both the grounds shorted(controller and system) as far as i understand. Is there anything i am missing here or should i use an external usb isolator to use the usb function. Please help me.

Regards,

Varaprasad.

  • 0
    TI__Guru 57255 points

    Hi Varaprasad,

    I will first restate your question to confirm that I understand it.  I'll then answer my question.

    Question:
    There appear to be two grounds in the F2806x ISO schematic.  One is a downward triangle ground and the other is the three-line ground (MCU ground/DIMM ground).  Page 2 is on three-line-ground, page 3 has both grounds on it, and page 4 is on triangle-ground.  The main question for you is: doesn't page 4 defeat the isolation is this board?

    Answer:
    It appears that the engineer who designed the controlCARD designed the schematic in a less than ideal way.  Within a page, OrCAD seems to connect all symbols that look the same to the same net.  However, when moving from one page to another, you should ignore the look of the symbols and only look at the netnames.  This means that Page 2 is on DGND, Page 3 has both grounds on it, and Page 4 is on DGND.

    It is worth noting that the USB peripheral interface on the controlCARD (J200 and associated circuitry) is not isolated from the C2000 MCU.  This can lead to potential issues if you plan on using USB at J200 and also plan to have the C2000 on the hot-side of an application.  This is because the remote PC will now be connected to the C2000's hot side ground.  If they indeed are using the C2000 on the hot-side, they should add isolation between J200 and the PC.


    Hopefully this answers your question as well.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Intellectual 460 points
    Hi Brett,

    Thanks for the help.

    Regards,
    Varaprasad.