SMT32F3 Differential ADC

[PNguyen]

Dear friends,

I'm setting a differential ADC input for my application.

The Positive voltage connects to ADC1_IN1 and the Negative connects to ADC1_IN2.

When I reading the 0V, the result I get is 1583 values of ADC (It is the raw data, I did not convert to voltage).

Do I forget something when setting the ADC? or I did something wrong in the config below?

My setup as below:

 hadc1.Instance = ADC1;

 hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV1;

 hadc1.Init.Resolution = ADC_RESOLUTION_12B;

 hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;

 hadc1.Init.ContinuousConvMode = DISABLE;

 hadc1.Init.DiscontinuousConvMode = DISABLE;

 hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_RISING;

 hadc1.Init.ExternalTrigConv = ADC_EXTERNALTRIGCONV_T1_CC1;

 hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;

 hadc1.Init.NbrOfConversion = 1;

 hadc1.Init.DMAContinuousRequests = DISABLE;

 hadc1.Init.EOCSelection = ADC_EOC_SEQ_CONV;

 hadc1.Init.LowPowerAutoWait = DISABLE;

 hadc1.Init.Overrun = ADC_OVR_DATA_OVERWRITTEN;

 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_1;

 sConfig.Rank = ADC_REGULAR_RANK_1;

 sConfig.SingleDiff = ADC_DIFFERENTIAL_ENDED;

 sConfig.SamplingTime = ADC_SAMPLETIME_4CYCLES_5;

 sConfig.OffsetNumber = ADC_OFFSET_NONE;

 sConfig.Offset = 0;

[Uwe Bonnes]

You forgot to tell what your VREF is. With VDDA/VREF=3.3V and VDD = 2.5v VDD measures as  2.5/3.3*2048 = 1551.5 That looks similar to your result.

[PNguyen]

Hi Uwe Bonnes,

The 1583 is the ADC value at the 0V differential voltage ADC input, and I didn't set the VREF. VDD is 3.3V.

I used a small package of STM32F303, so have no VREF pin.

And I read the Vref by ADC then the value is 1409, with the CALFACT_S value is 62.

The VREFINT_CAL (@ 0x1ffff7ba) is 1523; VREFINT_DATA (@ADC1->DR) is 1346