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MSP430F4784 and AtoD convertor error after power cycle

Louis Kovach
Prodigy 240 points
Other Parts Discussed in Thread: MSP430F4784

I am using a MSP430F4784 making a/d samples on each of the 4 channels. I have the inputs connected to a bench precision voltage source. I am receiving very stable A to D data with a consistent reading. Leaving everything the same except cycling power on the MSP430, I once again receive a stable signal but 6-8 counts plus or minus than the original each time the power is cycled. This error occurs in all channels and are offset by about the same amount.This leaves me to believe that the problem is in the common circuitry inside the A to D.

Is there something I need to do to correct this situation?

Thanks for the help,

   

  • 0
    Expert 2080 points

    I was working on some ADC12 those days, I discovered that the time to let internal vref  to settle while it is outsourced (on recommended 10uF and 100nF) take a "long" time.

    Perhaps, in your case, after a power cycle and the first time you make a conversion the vref is not yet stable.

  • 0 in reply to Argail
    Prodigy 240 points

    Argail, Thanks for the replay but I don't think this is the issue. because the values remain consistent during the entire time the CPU is powered. The only change that occurs is when the CPU power is cycled. In addition, I have discovered that it appears to be a gain vs a bias issue because the change in readings is proportional to the input voltage. Example 0.25v of input produces 1/2 the error counts as 0.50v of input.

  • 0 in reply to Louis Kovach
    Prodigy 240 points

    I am still struggling with this issue. Could someone from TI please respond if this is a characteristic of this part or I am misusing it in some way?

    Thanks for the help,

  • 0 in reply to Louis Kovach
    Guru 227245 points

    Which reference do you use?

    What about your power supply? maybe it changes a bit on each power cycle? If you use VCC as reference, a slight difference in VCC (even though VCC is stable at this changed value) will change the ADC result.

    Just a guess.

  • 0 in reply to Jens-Michael Gross
    Prodigy 240 points

    Jens-Michael Gross,

    Thanks for your idea. I am using a precision external voltage reference. This should be immune to changes in VCC. I appreciate your idea, I am still working on it but have not made any progress. I am hoping TI can shed some light and point me in the right direction. Thanks for the time. Lou

     

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