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STM32L476 DAC usable range and ADC offset

Question asked by Dan Hunter on Mar 13, 2018
Latest reply on Mar 14, 2018 by waclawek.jan

Using the Nucleo-L476RG development board for code development for a design prototype. What is the expected linear range of the DAC?

  • For the linear range, I am measuring the lower bound of the DAC about 55mV and upper bound about 3.271V.
  • Below and above this range the DAC rails. Vref (pin AVDD) is measured at 3.3191V.
  • This testing implies that the usable DAC range is approximately 70 counts to 4030 counts with resolution of 0.81mV/cnt (i.e. 3.319/4096 ... or 0.806mV/cnt if 3.3/4096), no?

 

 

If I execute the "ADC_SingleConversion_TriggerSW_IT" program, the following DAC values are used (per comments in code)

 

/* Set DAC output on 5 voltage levels, successively to: */
/* - minimum of full range (0 <=> ground 0V) */
/* - 1/4 of full range (4095 <=> Vdda=3.3V): 1023 <=> 0.825V */
/* - 1/2 of full range (4095 <=> Vdda=3.3V): 2048 <=> 1.65V */
/* - 3/4 of full range (4095 <=> Vdda=3.3V): 3071 <=> 2.475V */
/* - maximum of full range (4095 <=> Vdda=3.3V) */

 

What I obtain: 

DAC CNT|uhADCxConvertedData|uhADCxConvertedData_Voltage_mVolt|Measured DAC (LeCroy)

   0   |       0           |                 0V              |      55.4mV

1023   |     983           |              793mV              |       850mV

2048   |    2011           |             1.619V              |      1.680V

3071   |    3035           |             2.444V              |      2.500V

4095   |    3994           |             3.218V              |      3.271V

 

  • The calculated DAC voltage (from ADC) is approx 56mV in error compared to measured DAC voltage.
  • Is this an offset within the ADC and can this be calibrated out internally via HAL/MIX/LL calls or do I have to write an ADC calibration routine?

 

Issue: I am doing motor control and need to use an external Vref as a basis. The offsets in the DAC and ADC need to be calibrated out and the linear range of each conversion (DAC and ADC) is required

 

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