STM32f051R8 Vrefint channel HW requirements

[istepne]

Hi,

I am using STM32f051R8 for industrial controller application. I am using cubeMx tool to generate codes and Keil v5 to compile. 

One of my project requires to read accurate ADC channel read. 

So, I decided to read Vrefint channel to get best accuracy from the ADC channel. Vrefint channel gives always 4095 (12bits).

I took many hours to find out the problem. Finally, I found a logical error condition.

The tested code below, For testing, activated Ch0, Ch1, Ch15 and Vrefint channels and also DMA to read. 

I have two different application boards, (two different schematic) Board1 and Board2. 

When read Ch0,Ch1 and Ch15 are normal, but Vrefint channel always gives 4095 on Board1. 

But same code works on Board2! I tired 3 more boards and results are same. Three of the Board2 s are OK, three of the Board1 s are not.

Pin 13-32-64 are short circuited as Vdd=3.3V and also 12-31-63 pins are short circuited as GND.

In datasheet says that Vdda >=Vdd. In my situation Vdda=Vdd=3.3V

Please let me clear which points to check on hardware?

/**

 * @brief ADC Initialization Function

 * @param None

 * @retval None

 */

static void MX_ADC_Init(void)

{

 /* USER CODE BEGIN ADC_Init 0 */

 /* USER CODE END ADC_Init 0 */

 ADC_ChannelConfTypeDef sConfig = {0};

 /* USER CODE BEGIN ADC_Init 1 */

 /* USER CODE END ADC_Init 1 */

 /** Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion)

 */

 hadc.Instance = ADC1;

 hadc.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;

 hadc.Init.Resolution = ADC_RESOLUTION_12B;

 hadc.Init.DataAlign = ADC_DATAALIGN_RIGHT;

 hadc.Init.ScanConvMode = ADC_SCAN_DIRECTION_FORWARD;

 hadc.Init.EOCSelection = ADC_EOC_SEQ_CONV;

 hadc.Init.LowPowerAutoWait = DISABLE;

 hadc.Init.LowPowerAutoPowerOff = DISABLE;

 hadc.Init.ContinuousConvMode = ENABLE;

 hadc.Init.DiscontinuousConvMode = DISABLE;

 hadc.Init.ExternalTrigConv = ADC_SOFTWARE_START;

 hadc.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;

 hadc.Init.DMAContinuousRequests = DISABLE;

 hadc.Init.Overrun = ADC_OVR_DATA_PRESERVED;

 if (HAL_ADC_Init(&hadc) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure for the selected ADC regular channel to be converted.

 */

 sConfig.Channel = ADC_CHANNEL_0;

 sConfig.Rank = ADC_RANK_CHANNEL_NUMBER;

 sConfig.SamplingTime = ADC_SAMPLETIME_239CYCLES_5;

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

 {

  Error_Handler();

 }

 /** Configure for the selected ADC regular channel to be converted.

 */

 sConfig.Channel = ADC_CHANNEL_1;

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

 {

  Error_Handler();

 }

 /** Configure for the selected ADC regular channel to be converted.

 */

 sConfig.Channel = ADC_CHANNEL_15;

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

 {

  Error_Handler();

 }

 /** Configure for the selected ADC regular channel to be converted.

 */

 sConfig.Channel = ADC_CHANNEL_VREFINT;

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

 {

  Error_Handler();

 }

 /* USER CODE BEGIN ADC_Init 2 */

 /* USER CODE END ADC_Init 2 */

}

void DMA1_Channel1_IRQHandler(void)

{

 /* USER CODE BEGIN DMA1_Channel1_IRQn 0 */

 /* USER CODE END DMA1_Channel1_IRQn 0 */

 HAL_DMA_IRQHandler(&hdma_adc);

 /* USER CODE BEGIN DMA1_Channel1_IRQn 1 */

  devsta.tempReady=1;

  HAL_ADC_Start(&hadc);

 /* USER CODE END DMA1_Channel1_IRQn 1 */

}

Regards,

Murat