AT90USB1286-16MU ATMEL [ATMEL Corporation], AT90USB1286-16MU Datasheet - Page 323

• Manufacturer Part Number: AT90USB1286-16MU
• Description: Microcontroller with 64/128K Bytes of ISP Flash and USB Controller
• Manufacturer: ATMEL [ATMEL Corporation]

25.5.1
25.5.2
25.6
7593A–AVR–02/06
ADC Noise Canceler
ADC Input Channels
ADC Voltage Reference
The settling time and gain stage bandwidth is independent of the ADHSM bit setting.
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
When switching to a differential gain channel, the first conversion result may have a poor accu-
racy due to the required settling time for the automatic offset cancellation circuitry. The user
should preferably disregard the first conversion result.
The reference voltage for the ADC (V
ended channels that exceed V
either AV
AV
ated from the internal bandgap reference (V
external AREF pin is directly connected to the ADC, and the reference voltage can be made
more immune to noise by connecting a capacitor between the AREF pin and ground. V
also be measured at the AREF pin with a high impedant voltmeter. Note that V
impedant source, and only a capacitive load should be connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use the other
reference voltage options in the application, as they will be shorted to the external voltage. If no
external voltage is applied to the AREF pin, the user may switch between AV
reference selection. The first ADC conversion result after switching reference voltage source
may be inaccurate, and the user is advised to discard this result.
If differential channels are used, the selected reference should not be closer to AV
cated in
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise
induced from the CPU core and other I/O peripherals. The noise canceler can be used with ADC
Noise Reduction and Idle mode. To make use of this feature, the following procedure should be
used:
• In Single Conversion mode, always select the channel before starting the conversion. The
• In Free Running mode, always select the channel before starting the first conversion. The
CC
channel selection may be changed one ADC clock cycle after writing one to ADSC. However,
the simplest method is to wait for the conversion to complete before changing the channel
selection.
channel selection may be changed one ADC clock cycle after writing one to ADSC. However,
the simplest method is to wait for the first conversion to complete, and then change the
channel selection. Since the next conversion has already started automatically, the next
result will reflect the previous channel selection. Subsequent conversions will reflect the new
channel selection.
is connected to the ADC through a passive switch. The internal 2.56V reference is gener-
Table 30-5 on page
CC
, internal 2.56V reference, or external AREF pin.
407.
REF
will result in codes close to 0x3FF. V
REF
) indicates the conversion range for the ADC. Single
BG
) through an internal amplifier. In either case, the
AT90USB64/128
REF
can be selected as
CC
and 2.56V as
REF
CC
than indi-
is a high
REF
323
can