ATmega32U4 Atmel Corporation, ATmega32U4 Datasheet - Page 299

• Manufacturer Part Number: ATmega32U4
• Manufacturer: Atmel Corporation

Specifications of ATmega32U4

• Flash (kbytes): 32 Kbytes
• Pin Count: 44
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 14
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 26
• Ext Interrupts: 13
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• Spi: 2
• Twi (i2c): 1
• Uart: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 12
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 3.3
• Eeprom (bytes): 1024
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 4
• Output Compare Channels: 12
• Input Capture Channels: 2
• Pwm Channels: 8
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

24.5.1
24.5.2
24.6
7766F–AVR–11/10
Temperature Sensor
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 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 ATmega16U4/ATmega32U4 includes an on-chip temperature sensor, whose the value can
be read through the A/D Converter.
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC input. MUX[5..0] bits in ADMUX register enables the temperature sensor. The
nternal 2.56V voltage reference must also be selected for the ADC voltage reference source in
he temperature sensor measurement. When the temperature sensor is enabled, the ADC con-
verter can be used in single conversion mode to measure the voltage over the temperature
sensor.
• 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 29-5 on page
CC
, internal 2.56V reference, or external AREF pin.
384.
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
ATmega16/32U4
REF
can be selected as
CC
and 2.56V as
REF
CC
than indi-
is a high
REF
299
can