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Power cycling the f28m35x

Pat Harris
Genius 3890 points

Assuming the graphic did get loaded below, I have been power cycling a PCB with the same circuitry as the f28m35x PLC evaluation module. In doing so, I noticed some spikes on the +3.3, the +1.8, and the +1.2 volt test points in the circuit. I would like someone from TI to tell me if they see a problem with this performance. Could any of these spikes cause a problem for the CPU either singly or by accumulation?

The graphic is a rough sketch of the results. 

Thanks,

Pat

PLUS CCU V6 power cycling0001.PDF

  • 0
    TI__Expert 7885 points
    Hi Pat,

    Are all of these spikes simultaneous? Does the spike on the 1.8V rail not exceed 1.8V? From the linked image, it looks like the voltage on the 3.3V rail reaches 4.3V for 100us and the voltage on the 1.2V rail reaches 2.2V for 100us. Is this correct? Does it only happen during power-up?

    Best Regards,
    Adam Dunhoft
  • 0 in reply to Adam Dunhoft
    Genius 3890 points
    I cannot verify that the spikes are simultaneous. The spikes are intermittent and do appear to raise to a level of about 1 V above the rail. The 100 us is an approximation. These tests were run by interrupting the power source at a rate of from 2 to 10 Hz. I have only seen this at power up.
    We have submitted CPU samples for analysis after experiencing 8 failures in 75 PCBs that led to the CPU overheating. The analysis on three showed ESD damage, but there is a question concerning ground isolation of the 1.2v and 1.8v power.
    If there is a potential for spikes occurring through this non isolated ground condition, then we need to have a recommendation as to external circuitry that will compensate for this.
    Thanks,
    Pat