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Noisy ADC read-outs: seems to be function of power-up

tamir friedrich
Prodigy 40 points

Hello, I have a ADC related question , regarding calibration or power-up sequence:
Following a simple re-layout of the board, we are getting x10 noisier read-oust from the ADC's channels, for a reference HW based 0 volt  input. We found out it is possibly related to the power-up sequence of the voltage feeds, yet we are not sure about it.
Anyone experienced such a behaviour or can give me some directions to look for?

Your helpis much appreciated, Tamir, ACS tamirf@acsmotioncontrol.com

  • 0
    TI__Guru 60865 points

    Hi Tamir,

    Is the read out nosier (repeatedly sampling 0V gives a large code spread) or just offset from the original (repeatedly sampling gives a fairly consistent but large positive or negative offset) .  In the second case, there is probably some resistance in the ground between the ADC and signal being sampled that introduces some offset.  This can be pretty easily calibrated out of the system.  If it is the first case, you will probably need to hunt down the source of the noise and isolate it.  

  • 0 in reply to Devin Cottier
    Prodigy 40 points

    Hello Devin,
    It is an issue of a large and inconsistent spread of results, at certain cases of power-up it has the full swing of values. We ruled out all supplies as being the source of it, and tested in multiple samples and products. Soft-reset does not clear the issue, only a successful powering up. Thank you for your reply, Tamir

     

  • 0 in reply to tamir friedrich
    TI__Guru 60865 points

    Hi Tamir,

    Are you allowing the ADC at least 1ms to power up before taking samples?

  • 0
    Intellectual 810 points

    C2000 on-chip ADC is very difficult to use. sometimes it's inaccurate and at least difficult to predict its behavior. i think using off-chip ADC is a better solution although

    high resolution off-chip ADC needs some work on layout.

     

    Thanks

    Yu Cai