Datasheet

292
7766F–AVR–11/10
ATmega16/32U4
24. Analog to Digital Converter - ADC
24.1 Features
• 10/8-bit Resolution
• 0.5 LSB Integral Non-linearity
• ± 2 LSB Absolute Accuracy
• 65 - 260 µs Conversion Time
• Up to 15 kSPS at Maximum Resolution
• Twelve Multiplexed Single-Ended Input Channels
• One Differential amplifier providing gain of 1x - 10x - 40x - 200x
• Temperature sensor
• Optional Left Adjustment for ADC Result Readout
• 0 - V
CC
ADC Input Voltage Range
• Selectable 2.56 V 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
The ATmega16U4/ATmega32U4 features a 10-bit successive approximation ADC. The ADC is
connected to an 12-channel Analog Multiplexer which allows six single-ended voltage inputs
constructed from several pins of Port B, D and F. The single-ended voltage inputs refer to
0V (GND).
The device also supports 32 differential voltage input combinations, thanks to a differential
amplifier equipped with a programmable gain stage, providing amplification steps of 0 dB (1x),
10 dB (10x), 16dB (40x) or 23dB (200x) on the differential input voltage before the A/D conver-
sion. Two differential analog input channels share a common negative terminal (ADC0/ADC1),
while any other ADC input can be selected as the positive input terminal. If 1x, 10x or 40x gain is
used, 8-bit resolution can be expected. If 200x 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 24-1.
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 301 on how to connect this
pin.
Internal reference voltages of nominally 2.56V or AV
CC
are provided On-chip. The voltage refer-
ence may be externally decoupled at the AREF pin by a capacitor for better noise performance.