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.