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TMS320F28377D: How to understand the setting accuracy (LSB) and calculate the acquisition window value of F28377D's ADC

Sheldon He
Expert 8585 points
Part Number: TMS320F28377D

Hi All,

I have some difficulty in understanding the "setting accuracy" in calculating the acquisition window for ADC. What does the highlighted sentence in the picture below means? In my understanding, the setting accuracy should be something between 0.25 and 0.5, is that right? How could I choose the suitable "setting accuracy" in my project? Thanks!

 

  • 0
    TI__Guru 52030 points
    Sheldon,

    Do you know the output resistance of your signal, that you are connecting to the ADC?
    That is really all you need. Then choose how accurate you want your results to be, 0.5 LSB or 0.25 LSB.

    Finally plug it into the formula above.

    Lets say you picked 0.5 accuracy.

    t = -ln(0.5/4096)*(your_signals_output_resistance + 300)*(14.5*10^-12)

    After you get this t value, select the number of System clock cycles that would represent this value in your ADC register for acquisition time.
    Since you are using TMS320F28377D most likley you are running at 200MHz, which means system clock takes about 5ns.

    Lets say the value you get above for t is 70ns, then you must use 14-1 to write to ACQPS.

    Nima