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).
KFACTOR = 1.835 ÷ 1.82 when using G = 1.5 or when the gain calibration target voltage is 1.835. Otherwise, KFACTOR = 1.

On the example (M355_Adc) project is a different formula as folllows:

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)?

• HI,

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. 