ADC2 wrong internal calibration

Hi,

I'm experiencing problem with ADC2 internal calibration.

At initialisation of my program I start the calibration of both ADC, one after the other, and the ADC2 calib value seems always wrong. If I re-execute the calibration few seconds later I get another calibration offset for ADC2..

Here's the code I'm executing at initialization:

void DrvAdc::AdcCalibrate( )
{
   // Enable calibration mode (When this bit is set, the analog input channel multiplexer
   // is disconnected and the calibration reference voltage is connected to
   // the ADC core input)
   regADCPtr->calCR.bit.calEn = 1;

   // Clear HILO
   // Clear bridge enable
   // => Voltage Reference = (ADRefHi*R1 + ADRefLo*R2) / (R1 + R2)
   regADCPtr->calCR.bit.hilo = 0;
   regADCPtr->calCR.bit.bridgeEn = 0;

   // Value used to sum all result.
   uint32_t calSum = 0;
   // Calibration offset error...
   //for( uint16_t acq = 0; acq < 8; acq++ )
   {
      // start calibration conversion (single conversion)
      regADCPtr->calCR.bit.calSt = 1;

      // Wait until calibration is finished
      while( regADCPtr->calCR.bit.calSt != 0 );

      // read back result
      calSum += regADCPtr->calR.bit.adCalR;
   }

   // Calc mid-point calibration
   // Set HILO
   // => Voltage Reference = (ADRefLo*R1 + ADRefHi*R2) / (R1 + R2)
   regADCPtr->calCR.bit.hilo = 1;

   // Calibration offset error...
   //for( uint16_t acq = 0; acq < 8; acq++ )
   {
      // start calibration conversion (single conversion)
      regADCPtr->calCR.bit.calSt = 1;

      // Wait until calibration is finished
      while( regADCPtr->calCR.bit.calSt != 0 );

      // read back result
      calSum += regADCPtr->calR.bit.adCalR;
   }

   // Divide by 2 (1 volt ref + 1 volt ref) to get mid-point
   // We add 0x1 to round up the value. (Ex: For 16 acq, add 8/16(0,5))
   calSum = (calSum + 0x01) >> 1;

   // Calculate the compensate offset and apply it
   regADCPtr->calR.bit.adCalR = (0x800 - calSum);

   // Disable calibration and write back to 0 all other calibration variables
   regADCPtr->calCR.bit.calEn    = 0;
   regADCPtr->calCR.bit.hilo     = 0;
   regADCPtr->calCR.bit.bridgeEn = 0;
   regADCPtr->calCR.bit.calSt    = 0;

}

Here's the register adCalR values

After a power ON:

      ADC1:   adCalR = 4087

      ADC1:   adCalR = 854

If I re-execute the calibration after initialization:

     ADC1:   adCalR = 4087

     ADC1:   adCalR = 1189

Is it normal that both ADC calibration offset values are so different?

Is there a stabilisation time to wait before executing ADC calibration after a power-ON reset?

Thanks

David.