STM32U5 Analog input, can not read values under ~1,6V. With 12-bit resolution, it gets stuck in 2036 even if the voltage goes down.

[RomainR.]

Hello JAltu.1 (Community Member)

In order to help you, your request requires more details.

Can you indicate whether you use a custom board or Nucleo/Eval/DK?

The STM32U5 family has two different and independent ADC types (ADC1 and ADC4) which one do you use?

What is your VDDA/VREF schematic for the analog device section?

Finally, can you share your ADC/channel configuration code, input signal characteristics and the method by which you perform the conversion (polling, IT or DMA) ?

Best regards,

Romain,

[JAltu.1]

Hi @RomainR.​ 

It is a custom board.

I am using the ADC1.

The microcontroller is STM32U575CIU so it does not have VREF. VDDA is 3V3 and the connection is done with the recommended capcitors:

 

I am using the polling method and this is the channel configuration:

static void MX_ADC1_Init(void)

{

 /* USER CODE BEGIN ADC1_Init 0 */

  // get access to PWR

  SET_BIT(RCC->AHB3ENR, RCC_AHB3ENR_PWREN);

  // switch voltage monitor on

  SET_BIT(PWR->SVMCR, PWR_SVMCR_AVM1EN);

  // wait until ready

  while (READ_BIT(PWR->SVMSR, PWR_SVMSR_VDDA1RDY) == 0);

  // switch VDDA isolation off

  SET_BIT(PWR->SVMCR, PWR_SVMCR_ASV);

  // we do not need access to the PWR domain

  CLEAR_BIT(RCC->AHB3ENR, RCC_AHB3ENR_PWREN);

 /* USER CODE END ADC1_Init 0 */

 ADC_ChannelConfTypeDef sConfig = {0};

 /* USER CODE BEGIN ADC1_Init 1 */

 /* USER CODE END ADC1_Init 1 */

 /** Common config

 */

 hadc1.Instance = ADC1;

 hadc1.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;

 hadc1.Init.Resolution = ADC_RESOLUTION_12B;

 hadc1.Init.GainCompensation = 0;

 hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;

 hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;

 hadc1.Init.LowPowerAutoWait = 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.TriggerFrequencyMode = ADC_TRIGGER_FREQ_HIGH;

 hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;

 hadc1.Init.LeftBitShift = ADC_LEFTBITSHIFT_NONE;

 hadc1.Init.ConversionDataManagement = ADC_CONVERSIONDATA_DR;

 hadc1.Init.OversamplingMode = DISABLE;

 if (HAL_ADC_Init(&hadc1) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure Regular Channel

 */

 sConfig.Channel = ADC_CHANNEL_5;

 sConfig.Rank = ADC_REGULAR_RANK_1;

 sConfig.SamplingTime = ADC_SAMPLETIME_5CYCLE;

 sConfig.SingleDiff = ADC_SINGLE_ENDED;

 sConfig.OffsetNumber = ADC_OFFSET_NONE;

 sConfig.Offset = 0;

 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

 {

  Error_Handler();

 }

 /* USER CODE BEGIN ADC1_Init 2 */

 /* USER CODE END ADC1_Init 2 */

}

Than you

[JAltu.1]

Hi @RomainR. (ST Employee)​ 

It is a custom board.

I am using the ADC1.

The microcontroller is STM32U575CIU so it does not have VREF. VDDA is 3V3 and the connection is done with the recommended capcitors:

 

I am using the polling method and this is the channel configuration:

static void MX_ADC1_Init(void)

{

 /* USER CODE BEGIN ADC1_Init 0 */

  // get access to PWR

  SET_BIT(RCC->AHB3ENR, RCC_AHB3ENR_PWREN);

  // switch voltage monitor on

  SET_BIT(PWR->SVMCR, PWR_SVMCR_AVM1EN);

  // wait until ready

  while (READ_BIT(PWR->SVMSR, PWR_SVMSR_VDDA1RDY) == 0);

  // switch VDDA isolation off

  SET_BIT(PWR->SVMCR, PWR_SVMCR_ASV);

  // we do not need access to the PWR domain

  CLEAR_BIT(RCC->AHB3ENR, RCC_AHB3ENR_PWREN);

 /* USER CODE END ADC1_Init 0 */

 ADC_ChannelConfTypeDef sConfig = {0};

 /* USER CODE BEGIN ADC1_Init 1 */

 /* USER CODE END ADC1_Init 1 */

 /** Common config

 */

 hadc1.Instance = ADC1;

 hadc1.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;

 hadc1.Init.Resolution = ADC_RESOLUTION_12B;

 hadc1.Init.GainCompensation = 0;

 hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;

 hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;

 hadc1.Init.LowPowerAutoWait = 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.TriggerFrequencyMode = ADC_TRIGGER_FREQ_HIGH;

 hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;

 hadc1.Init.LeftBitShift = ADC_LEFTBITSHIFT_NONE;

 hadc1.Init.ConversionDataManagement = ADC_CONVERSIONDATA_DR;

 hadc1.Init.OversamplingMode = DISABLE;

 if (HAL_ADC_Init(&hadc1) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure Regular Channel

 */

 sConfig.Channel = ADC_CHANNEL_5;

 sConfig.Rank = ADC_REGULAR_RANK_1;

 sConfig.SamplingTime = ADC_SAMPLETIME_5CYCLE;

 sConfig.SingleDiff = ADC_SINGLE_ENDED;

 sConfig.OffsetNumber = ADC_OFFSET_NONE;

 sConfig.Offset = 0;

 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

 {

  Error_Handler();

 }

 /* USER CODE BEGIN ADC1_Init 2 */

 /* USER CODE END ADC1_Init 2 */

}

Than you

[RomainR.]

from your MX_ADC1_Init() function.

I see that you are doing an Enable PWR and VDDA supply. Then you do a Disable PWR Why ?

Can you simply replace following code :

/* USER CODE BEGIN ADC1_Init 0 */
  // get access to PWR
  SET_BIT(RCC->AHB3ENR, RCC_AHB3ENR_PWREN);
  // switch voltage monitor on
  SET_BIT(PWR->SVMCR, PWR_SVMCR_AVM1EN);
  // wait until ready
  while (READ_BIT(PWR->SVMSR, PWR_SVMSR_VDDA1RDY) == 0);
  // switch VDDA isolation off
  SET_BIT(PWR->SVMCR, PWR_SVMCR_ASV);
  // we do not need access to the PWR domain
  CLEAR_BIT(RCC->AHB3ENR, RCC_AHB3ENR_PWREN);
 /* USER CODE END ADC1_Init 0 */

By:

__HAL_RCC_PWR_CLK_ENABLE();
HAL_PWREx_EnableVddA();

Be sure you have also implemented HAL_ADC_MspInit(ADC_HandleTypeDef* hadc) function to :

- Configure and enable the clock source of ADC1.

- Configure also PA0 as Analog input and that is associated to your ADC1 Channel 5 (you also need to enable the clock for GPIOA)

Finally I recommend to calibrate the ADC1 once before using it:

HAL_ADCEx_Calibration_Start(&hadc1, ADC_CALIB_OFFSET, ADC_SINGLE_ENDED)

Let me know.

BR

Romain,

[JAltu.1]

I have changed the code to:

	__HAL_RCC_PWR_CLK_ENABLE();
	HAL_PWREx_EnableVddA();

I have implemented HAL_ADC_MspInit(ADC_HandleTypeDef* hadc) function and the calibration.

But i still have the same problem. The weird thing is that above 1.6V more or less, it returns correctly the values.

BR

[RomainR.]

Is it abnormal that your conversions have an offset equal to VDDA/2 ? 

What is your input voltage source, since you are configuring the ADC1 in single-ended mode, is your analog signal is correctly referenced to VSSA/VSS?

What is the ADC1 result conversion if you short PA0 directly to VSSA or VSS ?

Are you able to share your project firmware as an archive ?

BR

Romain,

[JAltu.1]

The input voltage source is a 4.2V battery with a voltage divider and the analog signal is correctly referenced to VSSA.

About the project, simplifying the code to this, the same thing happens:

  HAL_ADC_MspInit(&hadc1);
  HAL_ADC_Start(&hadc1);
  HAL_ADC_PollForConversion(&hadc1,100);
  Battery = HAL_ADC_GetValue(&hadc1);