What is the required timing between ADC initialization and calibration on the STM32G0B1?

[CSmit.4]

We are using the STM32G0B1CC and have noticed that if we call HAL_ADCEx_Calibration_Start() too soon after calling HAL_ADC_Init() that the CALFACT register comes back as 0. If we insert a substantial delay, say 20 ms between the 2 calls, CALFACT is populated with a reasonable value, and later conversions are considerably more accurate. HAL_ADCEx_Calibration_Start() in all cases returns HAL_OK. I'm trying to understand why the need for the delay:

void MX_ADC1_Init(void)

{

 ADC_ChannelConfTypeDef sConfig = {0};

 hadc1.Instance = ADC1;

 hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;

 hadc1.Init.Resolution = ADC_RESOLUTION_12B;

 hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;

 hadc1.Init.ScanConvMode = ADC_SCAN_SEQ_FIXED;

 hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;

 hadc1.Init.LowPowerAutoWait = DISABLE;

 hadc1.Init.LowPowerAutoPowerOff = DISABLE;

 hadc1.Init.ContinuousConvMode = DISABLE;

 hadc1.Init.NbrOfConversion = 1;

 hadc1.Init.DiscontinuousConvMode = DISABLE;

 hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;

 hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;

 hadc1.Init.DMAContinuousRequests = DISABLE;

 hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;

 hadc1.Init.SamplingTimeCommon1 = ADC_SAMPLETIME_160CYCLES_5;  

 hadc1.Init.OversamplingMode = DISABLE;

 hadc1.Init.TriggerFrequencyMode = ADC_TRIGGER_FREQ_HIGH;

 if (HAL_ADC_Init(&hadc1) != HAL_OK)

 {

  Error_Handler();

 }

 HAL_Delay(20);  

  

 HAL_ADC_Stop(&hadc1);

 HAL_ADCEx_Calibration_Start(&hadc1);

[RomainR.]

Hello @CSmit.4 (Community Member)

Remove HAL_ADC_Stop(&hadc1) because the HAL_ADCEx_Calibration_Start() disable ADC.

Make sure ADC clock frequency is:

fADC <= 35MHz for Range 1.

fADC <= 16MHz for Range 2.

Also, I suggest you either to try the following example:

STM32Cube\Repository\STM32Cube_FW_G0_V1.6.1\Projects\NUCLEO-G0B1RE\Examples\ADC\ADC_MultiChannelSingleConversion

Or to apply the check below at the end of your MX_ADC1_Init() :

void MX_ADC1_Init(void)
{
	ADC_ChannelConfTypeDef sConfig = {0};
 
	hadc1.Instance = ADC1;
	hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;
	hadc1.Init.Resolution = ADC_RESOLUTION_12B;
	hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
	hadc1.Init.ScanConvMode = ADC_SCAN_SEQ_FIXED;
	hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
	hadc1.Init.LowPowerAutoWait = DISABLE;
	hadc1.Init.LowPowerAutoPowerOff = DISABLE;
	hadc1.Init.ContinuousConvMode = DISABLE;
	hadc1.Init.NbrOfConversion = 1;
	hadc1.Init.DiscontinuousConvMode = DISABLE;
	hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
	hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
	hadc1.Init.DMAContinuousRequests = DISABLE;
	hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;
	hadc1.Init.SamplingTimeCommon1 = ADC_SAMPLETIME_160CYCLES_5; 
	hadc1.Init.OversamplingMode = DISABLE;
	hadc1.Init.TriggerFrequencyMode = ADC_TRIGGER_FREQ_HIGH;
 
	if (HAL_ADC_Init(&hadc1) != HAL_OK)
	{
		Error_Handler();
	}
 
	if (HAL_ADCEx_Calibration_Start(&hadc1) != HAL_OK)
	{
		Error_Handler();
	} 
}

Best regards,

Romain,

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[CSmit.4]

Thank you Romain. I tried your suggestions, but the problem persisted. I then finally realized the issue was a power sequencing one. The signal that provides the ADC reference voltage was asserted AFTER the ADC calibration was being performed.