ATmega32U4 Atmel Corporation, ATmega32U4 Datasheet - Page 300

• 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

24.6.1
7766F–AVR–11/10
Sensor Calibration
The temperature sensor and its internal driver are enabled when ADMUX value selects the tem-
perature sensor as ADC input. The propagation delay of this driver is approximatively 2µS.
Therefore two successive conversions are required. The correct temperature measurement will
be the second one.
One can also reduce this timing to one conversion by setting the ADMUX during the previous
conversion. Indeed the ADMUX can be programmed to select the temperature sensor just after
the beginning of the previous conversion start event and then the driver will be enabled 2 µS
before sampling and hold phase of temperature sensor measurement.
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
tor Calibration Register – OSCCAL” on page
two temperatures (+25°C and +85°C, with a tolerance of +/-10°C
temperature sensor value T
calibration value O
have an accurate 8MHz output) is stored in another memory zone.
Thanks to these four values and the linear characteristics of the temperature sensor and Internal
RC Oscillator, firmware can easily recalibrate the RC Oscillator on-the-go in function of the tem-
perature sensor measure
Figure 24-8. Linear Characterization of OSCCAL in function of T° measurement from ADC
Notes:
1. The temperature sensor calibration values cannot be used to do accurate temperature mea-
2. Be aware that if EESAVE fuse is left unprogrammed, any chip erase operation will
3. Accuracy results after a software recalibration of OSCCAL in function of T° will be
surements since the calibration temperature during production is not accurate (+/- 10°C)
clear the temperature sensor calibration values contained in EEPROM memory.
given when device will be fully characterized.
OSCCAL
O
O
2
1
i
(i.e. the value that should be set in OSCCAL register at this temperature to
(3)
(an application note describes the operation):
i
is measured and stored in EEPROM memory
T
1
T
2
32). During the production, a calibration is done at
T (ADC
ATmega16/32U4
(1)
). At each temperature, the
Section 6.5.1 ”Oscilla-
(2)
, and the OSCCAL
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