User Manual

242
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
8271E–AVR–07/2012
24. Analog-to-Digital Converter
24.1 Features
• 10-bit Resolution
• 0.5 LSB Integral Non-linearity
• ± 2 LSB Absolute Accuracy
• 13 - 260µs Conversion Time
• Up to 76.9kSPS (Up to 15kSPS at Maximum Resolution)
• 6 Multiplexed Single Ended Input Channels
• 2 Additional Multiplexed Single Ended Input Channels (TQFP and QFN/MLF Package only)
• Temperature Sensor Input Channel
• Optional Left Adjustment for ADC Result Readout
• 0 - V
CC
ADC Input Voltage Range
• Selectable 1.1V ADC Reference Voltage
• Free Running or Single Conversion Mode
• Interrupt on ADC Conversion Complete
• Sleep Mode Noise Canceler
24.2 Overview
The ATmega48A/PA/88A/PA/168A/PA/328/P features a 10-bit successive approximation ADC. The ADC is con-
nected to an 8-channel Analog Multiplexer which allows eight single-ended voltage inputs constructed from the
pins of Port A. The single-ended voltage inputs refer to 0V (GND).
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 24-1 on page 243.
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 248 on how to connect this pin.
Internal reference voltages of nominally 1.1V or AV
CC
are provided On-chip. The voltage reference may be exter-
nally decoupled at the AREF pin by a capacitor for better noise performance.
The Power Reduction ADC bit, PRADC, in ”Minimizing Power Consumption” on page 41 must be disabled by writ-
ing a logical zero to enable the ADC.
The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The mini-
mum value represents GND and the maximum value represents the voltage on the AREF pin minus 1 LSB.
Optionally, AV
CC
or an internal 1.1V reference voltage may be connected to the AREF pin by writing to the REFSn
bits in the ADMUX Register. The internal voltage reference may thus be decoupled by an external capacitor at the
AREF pin to improve noise immunity.