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C2000 LaunchPad circuit board and schematic diagram

David Taylor
Prodigy 200 points

The schematic diagram of the C2000 LaunchPad development kit shows two digital isolator chips (U5 = ISO7240, U7 = ISO7231), with zero ohm resistors (R16, R18, R19, R20, R21, R25, R28, R30, R32) in a bypass arrangement.

1. First of all, I can't visually locate the nine resistors mentioned above. I see their labels on the silk screen, but I can't see any resistors/shorts or pads. So my first question is, are these zero ohm resistors actually present or not? The BOM seems to indicate that they are present. Where are they? How come I can't see them?

2. Assuming that the zero ohm resistors are present, wouldn't they defeat the purpose of the two digital isolator chips? These two chips are certainly present on the board, but what is their function if they are being bypassed by short circuits?

3. There are two jumpers, J1 and J2, that can be used to electrically connect the 3.3V pins and the GND pins on the two sides of the digital isolator chips. But since there are already zero ohm bypass resistors located between these pins, wouldn't the jumpers be redundant?

It would be great if someone could help to eliminate my confusion on these points. Thanks!

David Taylor

  • 0
    TI__Guru 57255 points

    David,

    1) The resistors are physically located under the isolator chips (an image of the PCB is attached).  The resistors are therefore "Do Not Populate" by default.
    2) The purpose of these resistors is to provide a way to debug the emulator (or to bypass isolation of the emulator if isolation is not needed).
    3) The jumpers exists so that it easier to defeat isolation.  One potential use-case for this is when you don't have a baseboard to mate with the launchPAD but want to do some simple debugging/coding.


    Thank you,
    Brett