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ADC Error calculation

Manikandan M
Prodigy 105 points
Other Parts Discussed in Thread: SM320F28335-EP

Hello,

I am using SM320F28335-EP Microcontroller. My question about the accuracy of the internal ADC. I want accuracy the of 10mV. But I am considering all the as per the below calculation and I am achieving the worst possible error of 24mV.

Per the datasheet the INL =1.5LSB, DNL=1LSB, Offset(Zero code) = 15LSB, Gain error = 30LSB over the operting range.

I added all the possible error and i am getting

V Ref 2.048 V
Resolution 12 Bits
Number of steps 4095  
V resolution 0.5001221 mV
Zero code error 15 LSB 7.50183 mV
Gain error 30 LSB 15.0037 mV
Linearity error (INL) 2 LSB 1.00024 mV
Total possible error 24.00586081 mV

Please let me know how accurate this microcontroller is and how to tackle this problem. Or i need to use external ADC for this precise application.

Expecting earliest help from someone who worked on this processor.

Regards,

Manikandan.M

  • 0
    TI__Genius 16281 points

    Manikandan-

       Most people find simply adding the offset, gain, and INL a very pessimistic approximation of total error since those numbers represent worst case numbers across operating conditions and manufacturing process, but each parameter will not be worst case at the same conditions.  In absence of a total error spec, some will take the square root of the sum of squares of those errors.  However I must also point out that the full scale voltage for the 28335 is always 3.0V despite the reference voltage ( it is not ratiometric).  Therefore the correct LSB step size is actually ~732uV, so even using the approach I describe above, you'll be back to ~24mV total error.

      You may consider using a couple channels tied to known reference voltages to create calibration numbers so the ADC results can be compensated, but for that level of accuracy, perhaps an external ADC is best.