#4 – Stm32f103C8T6 ADC Vref internal voltage?

TA = 25 °C, VDD = 3.3 V (for the 2 V ≤ VDD ≤ 3.6 V voltage range)

As we look at the picture, value of analog reference voltage (Vref+) is connected to analog voltage  supply Vdda.

VDD = VDDA = VREF+

So if we calculate the adc value, it becomes as below:

#define VDDA  ((uint32_t)3300)  // (unit: mV)

Vadc = VDDA*adc_data/4095;

According to operating temperature VDDA value might change a little bit, but it can be ignored if the accuracy of adc is not so needed.