Hello,

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:

VIN = VREF × (((ADCDAT - 0x8000)/2^15) × KFACTOR) + ADCVBIAS_CAP where: |
(1) |

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)?