How to measure VBAT using ADC correctly in STM32L476 MCU

[eson]

Hi everyone!
I'm having trouble in measuring the VBAT through ADC. I'm using 3.3V power supply to the development board and when I measure VBAT through ADC, I'm getting values around 3.657V 

Here's my code:

void MX_ADC1_Init(void)
{

  /* USER CODE BEGIN ADC1_Init 0 */

  /* USER CODE END ADC1_Init 0 */

  ADC_MultiModeTypeDef multimode = {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.DataAlign = ADC_DATAALIGN_RIGHT;
  hadc1.Init.ScanConvMode = ADC_SCAN_ENABLE;
  hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
  hadc1.Init.LowPowerAutoWait = DISABLE;
  hadc1.Init.ContinuousConvMode = ENABLE;
  hadc1.Init.NbrOfConversion = 7;
  hadc1.Init.DiscontinuousConvMode = DISABLE;
  hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
  hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
  hadc1.Init.DMAContinuousRequests = ENABLE;
  hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;
  hadc1.Init.OversamplingMode = DISABLE;
  if (HAL_ADC_Init(&hadc1) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure the ADC multi-mode
  */
  multimode.Mode = ADC_MODE_INDEPENDENT;
  if (HAL_ADCEx_MultiModeConfigChannel(&hadc1, &multimode) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_VREFINT;
  sConfig.Rank = ADC_REGULAR_RANK_1;
  sConfig.SamplingTime = ADC_SAMPLETIME_247CYCLES_5;
  sConfig.SingleDiff = ADC_SINGLE_ENDED;
  sConfig.OffsetNumber = ADC_OFFSET_NONE;
  sConfig.Offset = 0;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_3;
  sConfig.Rank = ADC_REGULAR_RANK_2;
  sConfig.SamplingTime = ADC_SAMPLETIME_92CYCLES_5;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_4;
  sConfig.Rank = ADC_REGULAR_RANK_3;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_5;
  sConfig.Rank = ADC_REGULAR_RANK_4;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_7;
  sConfig.Rank = ADC_REGULAR_RANK_5;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_13;
  sConfig.Rank = ADC_REGULAR_RANK_6;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_VBAT;
  sConfig.Rank = ADC_REGULAR_RANK_7;
  sConfig.SamplingTime = ADC_SAMPLETIME_247CYCLES_5;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN ADC1_Init 2 */

  /* USER CODE END ADC1_Init 2 */

}​

/* USER CODE BEGIN PV */
uint16_t adc_data_buffer[7]; /* ADC常规转换数据 */

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
void PeriphCommonClock_Config(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{

  /* USER CODE BEGIN 1 */
  //NVIC_Redirect();
  /* USER CODE END 1 */

  /* MCU Configuration--------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* USER CODE BEGIN Init */

  /* USER CODE END Init */

  /* Configure the system clock */
  SystemClock_Config();

  /* Configure the peripherals common clocks */
  PeriphCommonClock_Config();

  /* USER CODE BEGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_ADC1_Init();
  MX_I2C2_Init();
  MX_I2C3_Init();
  MX_UART5_Init();
  MX_TIM2_Init();
  /* USER CODE BEGIN 2 */
  other_Init();

  // ADC Calibration
  HAL_ADCEx_Calibration_Start(&hadc1, ADC_SINGLE_ENDED);
  HAL_ADC_Start_DMA(&hadc1, (uint32_t *)adc_data_buffer, 7);

  /* USER CODE END 2 */

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

    /* USER CODE BEGIN 3 */
    ProcessADCValues(adc_data_buffer, 7);
    main_Task();
  }
  /* USER CODE END 3 */
}

void ProcessADCValues(volatile uint16_t *adcData, uint8_t length)
{
  for (uint8_t i = 0; i < length; i++)
  {
    // 处理每个通道的数据
    switch (i)
    {
    case 0:
      VREF_voltage = get_VREF(adcData[0]); // 
      break;
    case 1:
      ILIM_MonitorI = get_MP5087_ILIM(adcData[1]); // ADC channel 3, ilim_monitor
      break;
    case 2:
      ILIM_MonitorI2 = get_MP5087_ILIM(adcData[2]); // ADC channel 4, ilim_monitor1
      break;
    case 3:
      Tosa_temp1 = get_NBC103_Temp(adcData[3]); // ADC channel 5, TOSA_TEMP1
      break;
    case 4:
      Moudle_temp = get_TH05_Temp(adcData[4]); // ADC channel 7, module_temp
      break;
    case 5:
      Tosa_temp2 = get_NBC103_Temp(adcData[5]); // ADC channel 13, TOSA_TEMP2
      break;
    case 6:
      Vbat_voltage = get_Vbat(adcData[6], VREF_voltage);
      break;
    default:
      break;
    }
  }
}

#define VREFINT_ADDR ((uint16_t *)0x1FFF75AA) 

float get_VREF(uint16_t adc_value)
{
  uint16_t vrefint_cal = *VREFINT_ADDR;
  float vref_actual = (3.0f * vrefint_cal) / adc_value;
  return vref_actual;
}

float get_Vbat(uint16_t adc_value, float vref_voltage)
{
  float vbat = (adc_value * vref_voltage) / 4095.0f;
  return vbat;
}​

Can anyone please tell me where I'm doing it wrong?