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question regarding the fluctuating of AD conversion result

weifeng zheng
Prodigy 40 points
Other Parts Discussed in Thread: REF3020

In my case, a constant voltage with a value of 2.048 generated by REF3020 is connected directly to one AD pin. However, the conversion result of AD fluctuates between 2080 and 2096 when refleshing the watch window in CCS. On the other hand, different setting of the value of AD clock and hold window duration would result in different fluctuating range of converted digital value. Is fluctuating common? Could anyone help me? Many thanks.

  • 0
    Prodigy 40 points

    A further supplement, the type of DSP is TMS28335. Could anyone so kind to tell me how to configure the AD clock and hold window duration to achieve a stable and accurate conversion result?

  • 0 in reply to weifeng zheng
    TI__Genius 13786 points

    With a 2.048V input voltage I would expect a conversion result in the range of 2796 using this formula from the datasheet:

    4096*((VIN-ADCLO)/3  ( assuming ADCLO is connected to ground as is should be )

    4096*(2.048V/3.0V)

    The fact that you are getting mid range conversion results might be an indication the ADC input which is being converted is floating.  If you change the input voltage to 0V or 3V and see no appreciable change in the conversion results then likely the wrong channel has been selected.

    If the conversion results do change ( i.e. are close to 0 for 0V input or close to 4095 for 3V input ) then it is likely the ADC cal function is not being run ( please refer to section 4.7.3 int he datasheet for details ).