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weird behaviour on F2808....:-/

samuele^_^
Prodigy 170 points

Hi to Everybody!

I'm experiencing a strange problem with F2808.

I developed a sw for DC-DC converter, and the DSP makes 3 acquisitions on the ADC pins (the ADC is correctly configured for 3 acquisitions). However, another signal (output voltage) is at the input of ADCINB1 but it's not sampled, it's just there for future developments.

If the board boots up with ADCINB1 tied to GROUND, there's no problem, and everything works, but if it boots up with a voltage > 0 at ADCINB1, the DSP doesn't start at all, it cannot reach the first instruction. It looks like it were held in reset, but the reset signal is always high!...

all the boards have the same problem, so it's not a matter of some defect of the DSP....and of course it's not a sw problem, since the code is not run at all!....

Does anyone have a clue about this??! I really cannot understand...

I tried to change impedance at the ADC input,  then I tried to remove the REF3020 and set the internal ADC reference...and no results...

thank U

samuele....

  • Expert 1495 points

    Most probably your external signal connected to the analog input is powering up your microcontroller, through the internal clamping diodes.

    Regards,

    JayantD

  • in reply to Jayant Deshpande
    Prodigy 170 points

    thanks, that's could be definitely the reason, but do you think it's a normal behaviour?

    so the only thing I can do is avoiding to have a signal at the input of ADCINB1...

    by the way, since the DSP has internal clamping diodes, I didn't put external Schottky clamping diodes at the ADC inputs...is this a right practice?

    thankU!

    sam

     

  • in reply to samuele^_^
    Expert 1495 points

    This is perfectly normal. Avoiding an input signal may not be feasible in a real world application. What you need is a power supply supervisor. If your controller doesn't support power supply monitoring internally, an external chip may have to be used.

    External clamping diodes may be used as an additional precaution.

    All the best,

    JayantD