atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 318

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

25.5.1
25.5.2
25.6
25.6.1
318
Temperature Sensor
ATmega32U4
ADC Input Channels
ADC Voltage Reference
Sensor Calibration
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 impedance voltmeter. Note that V
impudent 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 ATmega32U4 includes an on-chip temperature sensor, whose the value can be read
through the A/D Converter.
The sensor initial tolerance is large (+/-10°C), but its characteristic is linear. Thus, if the applica-
tion requires accuracy, the firmware must include a calibration stage to use the sensor for direct
temperature measurement.
Another application of this sensor may concern the Internal Calibrated RC Oscillator, whose the
frequency can be adjusted by the user through the OSCCAL register (see
• 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.
404.
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
REF
Section 6.5.1 ”Oscilla-
can be selected as
CC
7766A–AVR–03/08
and 2.56V as
REF
CC
than indi-
is a high
REF
can