STM32H7 + Zephyr: ADC + DMA giving wrong (low) values for Internal temperature, VBAT, VREF

[DhirajThakur]

Hi,

we are using ADC with DMA for internal ADC channel like internal Temperature sensor, VBAT, VREF but we are facing issue related to accuracy please help me on this Configuration:

ADC channel:

   adc_channel_config_t ADC3_temp_config = {

        .channel       = ADC_CHANNEL_TEMPSENSOR,

        .rank          = ADC_REGULAR_RANK_8,

        .sampling_time = ADC_SAMPLETIME_810CYCLES_5,

    };

   adc_channel_config_t ADC3_vbat_config = {

        .channel       = ADC_CHANNEL_VBAT,

        .rank          = ADC_REGULAR_RANK_9,

        .sampling_time = ADC_SAMPLETIME_8CYCLES_5,

    };

        uC_AtoD_HAL::adc_channel_config_t ADC3_vref_config = {

        .channel       = ADC_CHANNEL_VREFINT,

        .rank          = ADC_REGULAR_RANK_10,

        .sampling_time = ADC_SAMPLETIME_8CYCLES_5,

};

 

DMA :

dma_channel_config_t ADC3_dma_config = {

        .channel = 2, // Channel 0 - ADC1, Channel 1 - ADC2, Channel 2 - ADC3, In H7 this parameter is used as a

                      // instance number

        .stream          = DMA1_Stream3,

        .src_data_width  = DMA_PDATAALIGN_WORD,

        .dest_data_width = DMA_MDATAALIGN_WORD

    };

 

ADC register for internal:

    ADC_Common_TypeDef *adc_common = ADC3_COMMON_REGISTER(pADC3Handler);

    adc_common->CCR |= ADC_CCR_TSEN | ADC_CCR_VREFEN | ADC_CCR_VBATEN;

 

Code:

For temperature:

#define TS_CAL1_TEMP 30.0f

#define TS_CAL2_TEMP 110.0f

#define TS_CAL1_ADDR ((uint16_t*)0x1FF1E820) // 30°C
#define TS_CAL2_ADDR ((uint16_t*)0x1FF1E840) // 110°C
uint16_t TS_CAL1 = *TS_CAL1_ADDR;
uint16_t TS_CAL2 = *TS_CAL2_ADDR;
LOG_DBG("TS_CAL1: %d, TS_CAL2: %d\n", TS_CAL1, TS_CAL2);
uint32_t TS_DATA = 0;
for (int i = 0; i < NUM_OF_CHANNEL_BUFFERS_ADC3; i++)
{
TS_DATA += MCUTemperature[i];
}
TS_DATA = TS_DATA / NUM_OF_CHANNEL_BUFFERS_ADC3;

float McuTemperature = (float_t)(((TS_CAL2_TEMP - TS_CAL1_TEMP) / (float_t)(TS_CAL2 - TS_CAL1)) * (TS_DATA - TS_CAL1)) + TS_CAL1_TEMP;

 

For Vref:

#define VREFIN_CAL ((uint16_t*)0x1FF1E860)
uint16_t Vrefin_Cal_Value = *VREFIN_CAL;
uint32_t VREF_DATA = 0;
for (int i = 0; i < NUM_OF_CHANNEL_BUFFERS_ADC3; i++)
{
VREF_DATA += Vrefint_volt[i];
}
VREF_DATA = VREF_DATA / NUM_OF_CHANNEL_BUFFERS_ADC3;
float vref = 3.3 * (Vrefin_Cal_Value /VREF_DATA );
vref = (vref / 65535) * VREF_DATA;

 

for Vbat:

    uint32_t Vbat_DATA = 0;

    for (int i = 0; i < NUM_OF_CHANNEL_BUFFERS_ADC3; i++)

    {

      Vbat_DATA += BatteryVoltage[i];

    }

    Vbat_DATA = Vbat_DATA / NUM_OF_CHANNEL_BUFFERS_ADC3;

   LOG_DBG("Vbat Raw count : %d\n",Vbat_DATA );

  BatteryVoltage = (Vbat_DATA * 4.0 * 3.3) / 65535.0;

 

Please let me know any configuration is miss 

Thanks in Advance

 

[TDK]

A few things:

• Are you calibrating the ADC before using it? You need to.
• What chip are you using?
• What raw ADC values do you get?
• What vbat//vrefint/temperature values do you get and, if not obvious, why do you think they're incorrect?
• You're using 130 for the upper end temperature instead of 110 as the comments say.

[DhirajThakur]

Are you calibrating the ADC before using it? You need to.

ANS: Yes

What chip are you using?

ANS: STM32H743ZIVET6

What raw ADC values do you get?

ANS: During debugging we could read the below calibration values and ADC raw count.

TS_CAL2 = 16287, TS_CAL1 = 12805.

Temperature raw count = 2877

Vbat raw count = 2760

 

You're using 130 for the upper end temperature instead of 110 as the comments say.

ANS:

#define TS_CAL1_TEMP 30.0f

#define TS_CAL2_TEMP 110.0f

 

What vbat//vrefint/temperature values do you get and, if not obvious, why do you think they're incorrect?

ANS:

We are using 16bit ADC 

For temperature,

As per the Datasheet of STM32H743ZI, an internal MCU temperature sensor connected to ADC3_INP18 channel is factory calibrated and below are the calibration values stored into the MCU internal Flash.

 

Below formula will be used for actual temperature calculation. Where TS_DATA is the actual temperature sensor output value converted by ADC. also mention this formula in code above 

 

At room temperature, it is expected to get the value of TS_DATA between TS_CAL1 & TS_CAL2 or near around TS_CAL1.  But we are getting TS_DATA = 2877 & calculated temperature = -198.098

For Vbat,

ADC count for Vbat/4  = 2760, formula used to calculate battery volt = 4 * 3.3 * Vbat raw count / 65535 , where 4 is multiplying factor for ADC count Vbat /4,  3.3 V is VDDA, 65535 is for 16 bit ADC resolution.

Hence Calculated Vbat = 0.56V

Measured Vbat pin voltage on STM32H743ZI Nucleo board is 3.25V. 

 

[Sarra.S]

Hello @DhirajThakur, 

Since the issue is related to TS_DATA value (very low), and this value is converted by ADC, most probably the issue is related to the ADC configuration; try using a longer sampling time for the internal temperature sensor.

Another thing is in your formula: Vbat= 4 * 3.3 * Vbat raw count / 65535 where VDDA= 3.3 

Depending on the package VDDA can be internally connected to Vref+ or not, could you specify the package you're using! 

[TDK]

> ADC_REGULAR_RANK_8

If converting 3 channels, they should be on ranks 1-3. Or maybe 0-2, not sure if it's base 0 or 1.

I have to believe the issue is in how the ADC is being configured. Doesn't look like you're using HAL. Ensure the SQRx registers point to the correct channels.

> ADC_SAMPLETIME_8CYCLES_5

Unlikely to be long enough for VREFINT or VBAT. Required sampling duration is in the datasheet.

[Billy OWEN]

Hi @DhirajThakur 

 

This post has been escalated to the ST Online Support Team for additional assistance.  We'll contact you directly.

 

Regards,

Billy