I use the EVAL-ADuCM355QSPZ Board and I try to read out the correct voltage value from ADC from a constant voltage source with 7 mV.
On the reference manual is a calculation formula as follwos.
To calculate the input voltage (VIN) for PGA gain = 1, use the following equation to convert ADC codes to a voltage:
VREF = 1.82 V (typical).ADCDAT is the ADC conversion result.KFACTOR = 1.835 ÷ 1.82 when using G = 1.5 or when the gain calibration target voltage is 1.835. Otherwise, KFACTOR = 1.ADCVBIAS_CAP = 1.11 V (typical).
On the example (M355_Adc) project is a different formula as folllows:
volt = (((RawData[ix]-32768.0)/65535*V_ADC_REF_mV*2)/1.5)+V_ADC_BIAS_mV; // ADC reference is trimmed to 1.82V and ADCVBIAS_CAP to 1.11V by this ATE test revision
The formula in this example project works fine only with a gain factor of 1.5.
With the formula from the reference manual i do not get a correct value.
If I will change the gain factor I get following adc raw values.
gain 1 = 12300; gain 1.5 = 3242 (correct); gain 2 = 64564
Questions: 1. What is the right formula to convert raw data to input voltage?
2. How must I calculate the gain factor in the formula?
3. Is there a different calculation between anolag input pins and sensor input (CH0 or CH1)?
An updated version of the user guide will be published on the external website in the coming weeks.
It has the appended extra information relating how to calculate a voltage from the ADC codes.
See the attachment.