NUCLEO-H563ZI - ADC reading noise when input grounded

[Iatik.1]

Hello, I’m trying to perform ADC measurements with the STM32H563ZIT. I’ve shared my configuration settings from the .ioc file below. The ADC reading fluctuates by about ±40. When I short the ADC pin to GND, the reading varies between 0 and 30 instead of staying stable. I can’t get a constant value. What could be causing this issue?

static void MX_ADC1_Init(void)
{

  /* USER CODE BEGIN ADC1_Init 0 */

  /* 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_DIV10;
  hadc1.Init.Resolution = ADC_RESOLUTION_12B;
  hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
  hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;
  hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
  hadc1.Init.LowPowerAutoWait = ENABLE;
  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.SamplingMode = ADC_SAMPLING_MODE_NORMAL;
  hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;
  hadc1.Init.OversamplingMode = ENABLE;
  hadc1.Init.Oversampling.Ratio = ADC_OVERSAMPLING_RATIO_16;
  hadc1.Init.Oversampling.RightBitShift = ADC_RIGHTBITSHIFT_4;
  hadc1.Init.Oversampling.TriggeredMode = ADC_TRIGGEREDMODE_SINGLE_TRIGGER;
  hadc1.Init.Oversampling.OversamplingStopReset = ADC_REGOVERSAMPLING_CONTINUED_MODE;
  if (HAL_ADC_Init(&hadc1) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_10;
  sConfig.Rank = ADC_REGULAR_RANK_1;
  sConfig.SamplingTime = ADC_SAMPLETIME_640CYCLES_5;
  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 */

}

void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure the main internal regulator output voltage
  */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE3);

  while(!__HAL_PWR_GET_FLAG(PWR_FLAG_VOSRDY)) {}

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE|RCC_OSCILLATORTYPE_CSI;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.CSIState = RCC_CSI_ON;
  RCC_OscInitStruct.CSICalibrationValue = RCC_CSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLL1_SOURCE_CSI;
  RCC_OscInitStruct.PLL.PLLM = 1;
  RCC_OscInitStruct.PLL.PLLN = 50;
  RCC_OscInitStruct.PLL.PLLP = 2;
  RCC_OscInitStruct.PLL.PLLQ = 2;
  RCC_OscInitStruct.PLL.PLLR = 2;
  RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1_VCIRANGE_2;
  RCC_OscInitStruct.PLL.PLLVCOSEL = RCC_PLL1_VCORANGE_WIDE;
  RCC_OscInitStruct.PLL.PLLFRACN = 0;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }

  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2
                              |RCC_CLOCKTYPE_PCLK3;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV4;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB3CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure the programming delay
  */
  __HAL_FLASH_SET_PROGRAM_DELAY(FLASH_PROGRAMMING_DELAY_2);
}

[TDK]

Are you calibrating the ADC before using it (this is required).

Custom board? Is VREF+/VDDA handled appropriately with decoupling caps? Show schematic.

[Iatik.1]

Yes, I'm calibrating it. I'm sharing the schematic file link.

https://www.st.com/resource/en/schematic_pack/mb1404-h563zi-c01-schematic.pdf 

  /* USER CODE BEGIN 2 */
  __HAL_RCC_ADC_CLK_ENABLE();
  LL_ADC_EnableInternalRegulator(ADC1);
  HAL_ADCEx_Calibration_Start(&hadc1, ADC_SINGLE_ENDED);

  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */

	  HAL_ADC_Start(&hadc1);
	  if(HAL_ADC_PollForConversion(&hadc1, 100) == HAL_OK)
	  {
		  adcValue = HAL_ADC_GetValue(&hadc1);
	  }
	  HAL_ADC_Stop(&hadc1);

[mƎALLEm]

Short wire length used? as it could be due to an antenna effect created by a long wire..

[TDK]

Not real sure. You should definitely be getting better performance than +/- 15 counts at 12b resolution when using max sample rate and oversampling.

Could be the way in which you're grounding the pin. How are you doing this exactly? Long wires can act as antennas.

If you measure an internal channel such as VREFINT, do you see the same variation?

[Iatik.1]

I am measuring Vref and getting a very stable result. I am performing the same test with the discovery board, and the results are correct.

[Andrew Neil]

as the others have said, it could be the way you're doing the "grounding".

Posting a (or some) good, clear photo(s) may help to see what's going on ...

[Iatik.1]

As I said, the discovery board is working fine, but I'm having problems with the H563 nucleo board. 

[Andrew Neil]

So photo of the H563 nucleo board, then.

[mƎALLEm]

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@Iatik.1 wrote:

As I said, the discovery board is working fine, but I'm having problems with the H563 nucleo board. 

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Using the same wire to ground the ADC input?