1.7 Voltage References

The application can choose between the following voltage references (VREF) for conversion results:
  • 12 bits, right adjusted
  • 8 bits, right adjusted
  • 12 bits, left adjusted
  • INT1V - Internal reference of 1.0V
  • INTVCC - Internal reference of VCC/1.6V
  • AREFA - External reference pin on PORTA
  • AREFB - External reference pin on PORTB
  • AVCC/2 – Internal reference of AVCC/2 for the XMEGA D devices

The internal INT1V reference is a 1.00V reference from the bandgap of the device. The bandgap voltage is 1.10V and the reference voltage is 10/11 of the bandgap voltage, giving the 1.00V reference. The accuracy of the reference is dependent on the bandgap. The accuracy of the bandgap is stated in the device’s data sheet.

The INTVCC is a reference voltage based on VCC divided by 1.6. The accuracy is depending on the accuracy and stability of the analog supply voltage (AVCC) and filtering should be used if the AVCC is connected to the digital VCC.

Note: The external reference pin AREFA/B is shared with the DAC module. The voltage reference is configured using the Reference Selection bitfield (REFSEL) in the Reference Control register (REFCTRL). The external reference is located at pin 0 on PORTA and PORTB (AREFA and AREFB).
Note: For the external references the maximum voltage to be used is VCC – 0.6V and the minimum voltage is 1V. The accuracy of the external reference is depending on the external circuitry and this has to be designed to satisfy the required accuracy for the ADC measurements.