DACREF datasheet(9/30 Pages) ATMEL

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AVR32768

32157A-AVR-12/10

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

ADCINx

Maximum input voltage: VVDDANA

Maximum external source

impedance,

•

without S/H: 3kΩ

•

with S/H: 1kΩ

Analog input

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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