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short circuit / SPI communication

MARK PESACH
Intellectual 850 points
Other Parts Discussed in Thread: TMS320F28377S

Hi

I have build a PCB board with the TMS320F28377S delfino and until now everything worked very well without any problems.

in the last couple of days i have "played" with  SPI communication protocol to MEMS sensor , and now i have a short circuit in my board ( i have measured 16ohm resistance between VDD and ground ) and it seems that the short circuit is inside the TMS320F28377S chip because as i connect voltage to the circuit he gets warm very fast (other components dosnt) . 

i am pretty sure that somehow i didnt used/connect the SPI signals properly and i damaged some I/O internal circuit .

the sensor i/O voltage is also 3.3V so i didnt used any buffer .

be happy if some one can advise me , maybe adding serial resistance or buffer will be a good practice?

best regards

Mark

  • 0
    TI__Expert 4810 points
    Mark,

    The other components on the board should not apply voltages to the F28377S before the F28377S is powered. You might check the power sequencing.

    You are correct that 3.3v signaling on the SPI should not require any buffering or isolation if there is a common VSS ground between the two. If the MEMS sensor (or any other component) is on a separate board and does not have a common ground then the relative voltage seen by the F28377S could be large and cause Electrical Over Stress (EOS) damage which could cause the short you are describing. If this is the case then a reference ground should be brought over from the MEMS sensor to VSS of the F28377S board.

    Best regards,
    Jason