AVR32768
7 ADC Analog-to-digital converter
The UC3 C analog-to-digital converter (ADC) has a fully differential 8/10/12-bit ADC
core with built-in sample and hold. It has multiple reference sources, and 1.5 mega-
samples per second conversion rate for 12 bit resolution. The ADC connections
require some electrical considerations, which are outlined in this section.
7.1 ADC analog Input
The ADC has 16 channels of analog input, ADCINx, which are GPIO multiplexed.
To get the best resolution, it is recommended not to use digital features of GPIO pins
close to the analog inputs used.
The analog input channels require a low enough external source impedance, which
depends on whether or not sample-and-hold is used (see Table 7-1).
For differential input, ADCIN[0:7] are used for positive input and ADCIN[8:15] are
used for negative input. In single-ended mode, all 16 channels can be used as single-
ended input. Please refer to the UC3 C datasheet for details.
Table 7-1. ADC analog inputs.
Signal name Recommended pin connection Description
Maximum input voltage: VVDDANA
Maximum external source
impedance,
ADCINx
Analog input
•
•
without S/H: 3kꢀ
with S/H: 1kꢀ
7.2 ADC voltage reference
The internal analog-to-digital converter in the UC3 C can use different voltage
references. Depending on the voltage references needed, the external voltage
reference pins should be connected as advised below.
7.2.1 ADC single-ended external reference (ADCREF0/ADCREF1)
Two external, single-ended voltage references are available. The maximum voltage
values depend on the power supply mode used. Refer to Table 7-2 and Table 7-3,
and Figure 7-1 and Figure 7-2.
If the single-ended external voltage references are not used, the pins can be left
unconnected and tied to internal pull-up through GPIO.
Figure 7-1. Single-ended external reference, 3.3V power supply mode.
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32157A-AVR-12/10
ATMEL [ ATMEL ]
