How can i get the Vbat actual value from ADC?

[MQasi.2]

Hello,

i'm using STM32G070, The firmware i have programmed converts the analog voltage to didital using ADC. the code is below:

the values i get from this is :

OUTPUT:

In the datasheet it is mention that a resister bridge for VBAT is 39K ohm which has ratio 3 on VBAT measurement .

so according to this the ADC value should be around 1365 which wil give us a voltage vaue of 1.1 but the result is voltage:0.48 and adc value:600.

please give me any suggestion, whats wrong with it.

thanks in advance.

[S.Ma]

I would do:

1- Configure the ADC and perform calibration if possible

2- Do your Vbat mesurement, the real value you will sense is Vbat / 3., the measurement is respective to Vdda for 2047 full scale 12 bit value. (3.0, 3.3, 3.6V etc... )

3- Run a Vref measurement to deduct VddA value in mV

4- Walk back the path to deduct accurately Vbat.

[Karl Yamashita]

Change the sampling time. I used the maximum value 640.5 cycles but you can play with other values. But I know the minimum (default) does not work as I get a lower voltage like ~1V. 

I did a initial calibration before the main while loop.

HAL_ADCEx_Calibration_Start(&hadc1, ADC_SINGLE_ENDED);

Measure the VREFP voltage and divide that by 4096 to get the ADC resolution.

#define ADC_RESOLUTION (3.259 / 4096) // my board measure 3.259V

void ADC_Check(void)
{
	char str[32] = {0};
	float adcVoltage;

	if(adc_data.adcRdy)
	{
		adc_data.adcRdy = false;
		adcVoltage = adc_data.adcValue * 3 * ADC_RESOLUTION;
		sprintf(str, "vbatt=%f, ADC_Value=0x%lX", adcVoltage, adc_data.adcValue);
		UART_DMA_NotifyUser(&uart2_msg, str, strlen(str), true);
	}
}

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