Datasheet

307
7593L–AVR–09/12
AT90USB64/128
26. ADC – Analog to Digital Converter
26.1 Features
• 10-bit resolution
• 0.5 LSB integral non-linearity
• ±2 LSB absolute accuracy
• 65 - 260µs conversion time
• Up to 15ksps at maximum resolution
• Eight multiplexed single ended input channels
• Seven differential input channels
• Optional left adjustment for ADC result readout
• 0 - V
CC
ADC input voltage range
• Selectable 2.56V 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
26.2 Overview
The Atmel AT90USB64/128 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 F. 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, providing
amplification steps of 0 dB (1×), 20 dB (10×), or 46 dB (200×) 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 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 308.
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 314 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.