Datasheet

244
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
23. ADC - Analog-to-digital converter
23.1 Features
• 10-bit resolution
• 0.5LSB integral non-linearity
• ±2LSB absolute accuracy
• 13 - 260µs conversion time
• Up to 15kSPS at maximum resolution
• Eight multiplexed single ended input channels
• Differential mode with selectable gain at 1×, 10×, or 200×
• Optional left adjustment for ADC result readout
• 0 - V
CC
ADC input voltage range
• 2.7 - V
CC
differential ADC voltage range
• Selectable 2.56V or 1.1V ADC reference voltage
• Free Running or Single Conversion mode
• ADC start conversion by auto triggering on interrupt sources
• Interrupt on ADC conversion complete
• Sleep mode noise canceler
Note: 1. The differential input channels are not tested for devices in PDIP package. This feature is only
guaranteed to work for devices in TQFP, VQFN/QFN/MLF, VFBGA and DRQFN packages.
23.2 Overview
The Atmel ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P features a 10-bit suc-
cessive approximation ADC. The ADC is connected to an 8-channel Analog Multiplexer which
allows 8 single-ended voltage inputs constructed from the pins of Port A. The single-ended volt-
age inputs refer to 0V (GND).
The device also supports 16 differential voltage input combinations. Two of the differential inputs
(ADC1, ADC0 and ADC3, ADC2) are equipped with a programmable gain stage. This provides
amplification steps of 0 dB (1×), 20 dB (10×), or 46 dB (200×) on the differential input voltage
before the A/D conversion. Seven differential analog input channels share a common negative
terminal (ADC1), while any other ADC input can be selected as the positive input terminal. If 1×
or 10× gain is used, 8-bit resolution can be expected. If 200× gain is used, 6-bit resolution can
be expected. Note that internal references of 1.1V should not be used on 10× and 200× gain.
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is
held at a constant level during conversion. A block diagram of the ADC is shown in Figure 23-1
on page 245.
The ADC has a separate analog supply voltage pin, AV
CC
. AV
CC
must not differ more than ±0.3V
from V
CC
. See the paragraph ”ADC Noise Canceler” on page 252 on how to connect this pin.
Internal reference voltages of nominally 1.1V, 2.56V, or AV
CC
are provided On-chip. The voltage
reference may be externally decoupled at the AREF pin by a capacitor for better noise perfor-
mance. If V
CC
is below 2.1V, internal voltage reference of 1.1V should not be used on single
ended channels.