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SPikes in ADC readings

Zac Bogart
Prodigy 30 points


We are using a 28335 and we're getting spikes in the ADC readings.  The spikes come and go, but interestingly seem to be specific sizes (e.g. 40 counts, sometimes 15 counts).  They come on all channels.  We think we've tried everything, but obviously we have not.  Normally the ADC readings are rock solid, maybe +/- 1 count.  Then we get a reading with a spike.  There is noise in the system (any system) but the analog voltages are and reference pins are both heavily bypassed and bypassed with smaller, fast, caps.   I have seen this post:

http://e2e.ti.com/support/microcontrollers/tms320c2000_32-bit_real-time_mcus/f/171/p/71975/261681.aspx

It is marked as having the question answered, but there is not a real answer.

Does anyone have any advice?


THanks

 

Zac

  • 0
    TI__Guru 55700 points

    Zac,

    Can you please answer the following questions:

    (1) Dynamic range of the input voltage sampled?

    (2) Did you trying sampling at lower frequency? Did you  trying varying the ADC clock and / or sampling window size?

    (3) Are you using internal reference (or) external reference voltage?

    (4) I understand that you try to reduce the spikes using bypass capacitors, but did you scope your analog voltage to check the noise levels

    (5) Do you see these spikes in ADC output when you provide DC voltage to ADC input?

    (6) Do you provide bypass caps on the ADC input channels?

    (7) Do you believe the ADC readings violates the ADC electrical characteristics provided in Pg 168 of datasheet?

     

    Regards,

    Manoj