Datasheet

241
8272A–AVR–01/10
164A/164PA/324A/324PA/644A/644PA/1284/1284P
22. ADC - Analog-to-digital Converter
22.1 Features
• 10-bit Resolution
• 0.5 LSB Integral Non-linearity
• ±2 LSB Absolute Accuracy
• 13 - 260 µs Conversion Time
• Up to 15 kSPS at Maximum Resolution
• 8 Multiplexed Single Ended Input Channels
• Differential mode with selectable gain at 1x, 10x or 200x
• 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.
22.2 Overview
The ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P features a 10-bit successive
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 voltage 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 (1x), 20 dB (10x), or 46 dB (200x) 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 1x
or 10x gain is used, 8-bit resolution can be expected. If 200x gain is used, 6-bit resolution can be
expected. Note that internal references of 1.1V should not be used on 10x and 200x 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 22-1
on page 242.
The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than
±0.3 V from V
CC
. See the paragraph ”ADC Noise Canceler” on page 249 on how to connect this
pin.
Internal reference voltages of nominally 1.1V, 2.56V or AVCC 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.