234
4317I–AVR–01/08
AT90PWM2/3/2B/3B
21. Analog to Digital Converter - ADC
21.1
Features
•
10-bit Resolution
•
0.5 LSB Integral Non-linearity
•
± 2 LSB Absolute Accuracy
•
8- 320 µs Conversion Time
•
Up to 125 kSPS at Maximum Resolution
•
11 Multiplexed Single Ended Input Channels
•
Two Differential input channels with accurate programmable gain 5, 10, 20 and 40
•
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 AT90PWM2/2B/3/3B features a 10-bit successive approximation ADC. The ADC is con-
nected to an 15-channel Analog Multiplexer which allows eleven single-ended input. The single-
ended voltage inputs refer to 0V (GND).
The device also supports 2 differential voltage input combinations which are equipped with a
programmable gain stage, providing amplification steps of 14dB (5x), 20 dB (10x), 26 dB (20x),
or 32dB (40x) on the differential input voltage before the A/D conversion. On the amplified chan-
nels, 8-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
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 241
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.
