INTERNAL TEMPERATURE SENSOR: Reading false value (STM32L152RE)

[TUmsc.1]

Hello all,

I am working with the STM32L152RE and want to read out the internal temperature sensor of the mikrocontroller. My code is the following:

#define TS_CAL1 *((uint16_t*) 0x1FF800FA) // 30 °C

#define TS_CAL2 *((uint16_t*) 0x1FF800FE) // 10 °C

double Get_Temp(void)

{

   ADC_ChannelConfTypeDef sConfig = {0};

   HAL_StatusTypeDef Res;

// GLOBAL CONFIGURATION

hadc.Instance = ADC1;

hadc.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;

hadc.Init.Resolution = ADC_RESOLUTION_12B;

hadc.Init.DataAlign = ADC_DATAALIGN_RIGHT;

hadc.Init.ScanConvMode = ADC_SCAN_DISABLE;

hadc.Init.EOCSelection = ADC_EOC_SINGLE_CONV;

hadc.Init.LowPowerAutoWait = ADC_AUTOWAIT_DISABLE;

hadc.Init.LowPowerAutoPowerOff = ADC_AUTOPOWEROFF_DISABLE;

hadc.Init.ChannelsBank = ADC_CHANNELS_BANK_A;

hadc.Init.ContinuousConvMode = DISABLE;

hadc.Init.NbrOfConversion = 1;

hadc.Init.DiscontinuousConvMode = DISABLE;

hadc.Init.ExternalTrigConv = ADC_SOFTWARE_START;

hadc.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;

hadc.Init.DMAContinuousRequests = DISABLE;

Res = HAL_ADC_Init(&hadc); // HAL_OK

  // CHANNEL CONFIGURATION

   sConfig.Rank     = 1;

   sConfig.SamplingTime = ADC_SAMPLETIME_384CYCLES;

   sConfig.Channel = ADC_CHANNEL_TEMPSENSOR;

   Res = HAL_ADC_ConfigChannel(&hadc, &sConfig); // HAL_OK

   // WAKE UP TEMPERATURE SENSOR

   ADC->CCR |= (uint32_t)ADC_CCR_TSVREFE;

   // WAIT FOR STABILIZATION (datasheet: >10 microseconds)

   HAL_Delay(100);

   // START ADC CONVERSION

   Res = HAL_ADC_Start(&hadc); // HAL_OK

   Res = HAL_ADC_PollForConversion(&hadc, 100); // HAL_OK

   Res = HAL_ADC_Stop(&hadc); // HAL_OK

   // READ RESULTING DATA

   int TempAdc = HAL_ADC_GetValue(&hadc); // 589

  // CALCULATE TEMPERATURE

  int CAL1 = TS_CAL1; // 663

  int CAL2 = TS_CAL2; // 845

double Slope = (110-30)/(double)(CAL2-CAL1); // 0.4395

double Degree = (Slope * (TempAdc-CAL1)) + 30; // -2.5274 °C

return Degree;

}

So the problem is, that I read and calc the temperature -2,5 °C. It should be about 22 °C. I did the instructions in the reference manual (RM0038 page 287) and consider the spezifications in the datasheet (page 112). I know the accuracy of TS_CAL1 and TS_CAL2 is +-5°C but I think this value ist too small.

I am grateful for any help.

Best regards,

Tobias

[Kraal · Accepted solution]

Hi,

This is funny, I had the exact same problem this afternoon, however on a L452 device, but I believe it is the same issue.

The TS_CAL values are measured with 3.0 Vcc supply voltage. I suppose that like me your system has 3.3 Vcc supply voltage.

Apply a x1.1 correction factor on the TempAdc, and you shoud get the right value of around 23°C.

Best regards,

Kraal

[TUmsc.1]

Thank you! That solved the problem.

For others who have the same problem, one more addition: The factor 1.1 is calculated by 3.3/3.0

Best regards,

Tobias