at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 193

• Manufacturer Part Number: at90pwm81-16se
• Description: 8-bit Avr Microcontroller With 8k Bytes In- System Programmable Flash
• Manufacturer: ATMEL Corporation

16.4.1
7734M–AVR–03/10
Manufacturing Calibration
described in Table 16-1. When the voltage reference equals 2.56V, the conversion result has approxi-
mately a 1 LSB/°C (or 2.5 mV/°C) correlation to temperature and the typical accuracy of the temperature
measurement is +/- 10°C after offset calibration.
Table 16-1.
The values described in Table 16-1 are typical values. However, due to the process variation the tempera-
ture sensor output voltage varies from one chip to another. To be capable of achieving more accurate
results the temperature measurement can be calibrated in the application software.
When using temperature sensor, the temperature (in Kelvin) is calculated as follows:
T = A * Tptat + B, where
Example:
If A=0x80 (=1.00) and B=8, and ADC result is 0x15E (=350), this gives a measured temperature of:
T = 1.00 * 350 + 8 = 358 K (+85°C)
One can also use the calibration values available in the signature row
from Software” on page
The calibration values are determined from values measured during test at room temperature
which is approximatively +25°C. Calibration measures are done at Vcc = 3V and with ADC in internal
Vref (1.1V) mode.
The temperature in Celsius degrees can be calculated utilizing the formula:
T = ((([ (ADCH << 8) | ADCL ] -(273 + 25-TSOFFSET)) * TSGAIN)/128) + 25
Where:
a. ADCH & ADCL are the ADC data registers,
b. TSGAIN is the temperature sensor gain (unsigned fixed point 8-bit temperature sensor gain factor in
1/128th units stored as previously in the signature row at address 0x0007)
Row from Software” on page
c. TSOFFSET is the temperature sensor offset correction term (signed twos complement 7-bit temperature
sensor offset reading stored as previously in the signature row at address 0x0005)
Temperature
Voltage (mV)
ADC
A Gain correction multiplier (constant '1', or unsigned fixed point number)
B Offset correction term (2. complement signed byte)
Tptat ADC result when measuring temperature sensor voltage, Vref with 2.56V internal reference
T Temperature in Kelvin ('K = 'C + 273)
Temperature vs. Sensor Output Voltage (Typical Case)
243.
-40°C
600
240
243.
25°C
762
305
105°C
See “Reading the Signature Row
See “Reading the Signature
125°C
1012
405
AT90PWM81
193