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TMS320F28377D: ADC: offset compensation error on ADCin14 and ADCIN15?

AnBer
Mastermind 30160 points
Part Number: TMS320F28377D

Team,

Assuming that we need a manual calibration for the ADC to get more precise measurement:

-What do we advise to do with pin ADCIN14/ADCIN15?
-On ADCIN15: Is a voltage divider with resistor enough? Should a reference IC be used?
-Is a cap needed on ADCIN14 for GND?
-Do we have some reference schematics? or are some examples available on the F2837xx LP boards?

Thanks in advance,

A.

  • 0
    TI__Guru 60865 points

    Hi AnBer,

    Your eventual measurement will only be as accurate as your calibration voltage. 

    Considering the ADCs on the F28x7x family of devices are already reasonably accurate (typical accuracy is about 0.1%) if you just use a voltage divider with say 1% tolerance resistors, then the calibration will result in lower accuracy, not increased accuracy.

    See a pretty in depth discussion about achievable accuracy with on-line self calibration here:

    https://e2e.ti.com/support/microcontrollers/c2000/f/171/t/587441

    If you provide a calibration voltage to the ADC, certainly you need to do all the normal ADC input design considerations to ensure the input has proper settling in the allocated S+H time (S+H settling error is unpredictable and will go straight to the overall accuracy of the system).  Since the calibration voltage presumably won't need to be sampled often, a 'charge-sharing' input design seems reasonable.  This would use a capacitor on the pin that is at least  as large as Ch*2^(N+1).  For 12-bit resolution with 14.5pF Ch, this will give you something in the ballpark of 120nF.  You'd want to make sure your source is capable of driving such a large capacitive load while remaining stable.