STM32G071 ADC problem

[JuM]

Using a STM32G071RBT6 on a Nucleo-64 board. Board is powered by its USB ​port.

According to user manual schematic VREF+ is connected to VDD (jumpers are installed).

At CN6.4 (VDD) we measure 3.322 V against CN6.6 (GND).

ADC is calibrated, CALFACT varying between 0x2A and 0x2B.

Sampling is max (160.5 us), and conversions single/polling.

Now trying to measure VDDA according to User Manual Chap. 14.9:

"The embedded internal voltage reference (VREFINT) and its calibration data acquired by the ADC during the manufacturing process at VDDA = 3.3 V can be used to evaluate the actual VDDA voltage level.

The following formula gives the actual VDDA voltage supplying the device: VDDA = 3 V x VREFINT_CAL / VREFINT_DATA."

3.0 V or 3.3 V... ?

We read

for VREFINT_CAL: 0x0683

for VREFINT_DATA (CH13) we read 0x05D6

Calculated VDDA gives 3.679 V (3.3V) or 3.345 (3.0V).>

What is wrong ?

Also problem with internal temperature sensor:

TS_CAL1 reads 0x0407, TS_CAL2 reads 0x055F.

TS_DATA (CH12) reads 0x03E0 (Nucleo board open air on desktop).

With formula we get -301.37 °C (VDDA==3.345V)...

What' wrong here ?

Regards Juergen

[Olek1]

@JuM​  Did you find out what is wrong? I also have a problem with STM32G0 and ADC.

My Vintref measure is incorrect.

[JuM]

Hi Olek, had these problems

• Vdda read/calculated via ADC did not match Vdda measured with a 61/2 digit multimeter, so had to adjust binary value
• The CALIB values are 12 bit, so if uisng lower ADC resolution (10, 8, 6) one must round down CALIB values before calculating.
• Readings were very unstable on Nucleo G071 board using Vdda, so we switched to internal 2.500 V reference:

void ADCSetVref2500 (void)
{
    uint32_t temp32;
    
 
    //---- Enable clock for VREFBUF ----//
    //
    temp32       = RCC->APBENR2;
    temp32      |= (RCC_APBENR2_SYSCFGEN);
    RCC->APBENR2 = temp32;
    
 
    temp32       = VREFBUF->CSR;                        // should be 0x0000 0002 (HIZ==1) after Reset
    temp32      &= ~(VREFBUF_CSR_VRR | VREFBUF_CSR_VRS | VREFBUF_CSR_HIZ | VREFBUF_CSR_ENVR);
    VREFBUF->CSR = temp32;
    
    
    //---- 2.500 V connected to pin VREF+ ----//
    //
    temp32 |= (VREFBUF_CSR_ENVR | VREFBUF_CSR_VRS);     // ENVR == 0x01 , VRS == 0x04
    VREFBUF->CSR = temp32;
    
} // of void ADCSetVref2500 (void)
    

[RSali.374]

Hi @JuM, @Community member​ 

Did you try to calibrate the ADC before?

HAL_StatusTypeDef HAL_ADCEx_Calibration_Start(ADC_HandleTypeDef* hadc)