SLAZ296AC October   2012  – August 2021 MSP430F5505

 

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6.2 ADC31

ADC Module

Category

Functional

Function

Sporadic occurrence of false ADC conversion results

Description

Sporadic errors in the ADC conversion results occur when the input voltage is an integer fraction of the reference voltage Vref. The probability of these sporadic errors is extremely low but possible. The false ADC results deviate from the actual input value depending on which integer fraction of Vref the input voltage is; for example:

- With Vin= 1/2 Vref, the most significant bit of the ADC conversion result might be affected, thus affecting all the bits that follow the most significant bit and, therefore, a completely wrong reading that ranges anywhere in the ADC range might be read.
- With Vin = 1/4 or 3/4 Vref, the second most significant bit along with all the bits that follow this bit are affected. In this case, the false reading is confined to one-half of the ADC range (as the first most significant bit value is correct).
- With Vin = 1/8, 3/8, 5/8, or 7/8 Vref, the third most significant bit and all the bits that follow this bit are affected. The false reading is confined to one-fourth of the ADC range (as the first two most significant bit values are correct)
- Similarly this behavior continues to the last bit.

Workaround

For measuring dc signals: Depending on the dc signal range being measured, discard the obvious outliers in measurement results and average out the false reading for errors in the lower bits.
For measuring ac signals: If possible, use a higher over-sampling rate to average out the error readings.