Datasheet

Table Of Contents
268
ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]
2549Q–AVR–02/2014
26. ADC – Analog to Digital Converter
26.1 Features
10-bit Resolution
1 LSB Integral Non-linearity
±2 LSB Absolute Accuracy
13µs - 260µs Conversion Time
Up to 76.9kSPS (Up to 15kSPS at Maximum Resolution)
16 Multiplexed Single Ended Input Channels
14 Differential input channels
4 Differential Input Channels with Optional Gain of 10× and 200×
Optional Left Adjustment for ADC Result Readout
0V - V
CC
ADC Input Voltage Range
2.7V - V
CC
Differential ADC Voltage Range
Selectable 2.56V or 1.1V ADC Reference Voltage
Free Running or Single Conversion Mode
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler
The ATmega640/1280/1281/2560/2561 features a 10-bit successive approximation ADC. The ADC is connected to
an 8/16-channel Analog Multiplexer which allows eight/sixteen single-ended voltage inputs constructed from the
pins of Port F and Port K. The single-ended voltage inputs refer to 0V (GND).
The device also supports 16/32 differential voltage input combinations. Four of the differential inputs (ADC1 &
ADC0, ADC3 & ADC2, ADC9 & ADC8 and ADC11 & ADC10) are equipped with a programmable gain stage, pro-
viding amplification steps of 0 dB (1×), 20 dB (10×) or 46 dB (200×) on the differential input voltage before the ADC
conversion. The 16 channels are split in two sections of 8 channels where in each section seven differential analog
input channels share a common negative terminal (ADC1/ADC9), while any other ADC input in that section 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, 7 bit resolution can be expected.
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 26-1 on page 269.
The ADC has a separate analog supply voltage pin, AVCC. AV
CC
must not differ more than ±0.3V from V
CC
. See
the paragraph “ADC Noise Canceler” on page 275 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 performance.
The Power Reduction ADC bit, PRADC, in “PRR0 – Power Reduction Register 0” on page 55 must be disabled by
writing a logical zero to enable the ADC.