Analog read is not returning the maximum value

Hi there.

I was making some tests and I have observed that, when I shortcircuit 3V3 into my analog pin (in this case PA0), the reading I'm having is 4022 instead of 4095.

Why this difference? I'm using HAL libraries as follows:

//Function to obtain ADC value
uint32_t adc_get_value(uint8_t channel)
{
 uint32_t value;
 uint32_t adcChannel;
 
 ADC_ChannelConfTypeDef sConfig;
 GPIO_InitTypeDef GPIO_InitStruct;
 
 //Returns ADC channel and sets up GPIO port
 adcChannel = adc_get_channel(channel, &GPIO_InitStruct);
 
 /* Configuration of channel on ADCx regular group on sequencer rank 1 */ 
 sConfig.Channel = adcChannel; /* Sampled channel number */
 
 
 sConfig.SamplingTime = ADC_SAMPLETIME_1CYCLE_5; /* Minimum sampling time */
 sConfig.Rank = ADC_REGULAR_RANK_1; /* Rank of sampled channel number ADCx_CHANNEL */
 
 if (HAL_ADC_ConfigChannel(&adc_handle_, &sConfig) != HAL_OK)
 {
 /* Channel Configuration Error */
 return -1;
 }
 
 if(HAL_ADC_Start(&adc_handle_) != HAL_OK)
 {
 /* Enables ADC Error */
 return -1;
 }
 
 if (HAL_ADC_PollForConversion(&adc_handle_, 10) != HAL_OK)
 {
 /* Poll for conversion Error */
 return -1;
 }
 
 value = HAL_ADC_GetValue(&adc_handle_);
 
 if (HAL_ADC_Stop(&adc_handle_) != HAL_OK)
 {
 /* Stop ADC conversion Error */
 return -1;
 }
 
 return value;
}

Thank you in advance!

Areify ~