ATA5771 ATMEL Corporation, ATA5771 Datasheet - Page 196

• Manufacturer Part Number: ATA5771
• Manufacturer: ATMEL Corporation

16.12 Temperature Measurement
144
ATtiny24/44/84
As default the ADC converter operates in the unipolar input mode, but the bipolar input mode
can be selected by writting the BIN bit in the ADCSRB to one. In the bipolar input mode two-
sided voltage differences are allowed and thus the voltage on the negative input pin can also be
larger than the voltage on the positive input pin.
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC8 channel. Selecting the ADC8 channel by writing the MUX5:0 bits in ADMUX
register to “100010” enables the temperature sensor. The internal 1.1V reference must also be
selected for the ADC reference source in the temperature sensor measurement. When the tem-
perature sensor is enabled, the ADC converter can be used in single conversion mode to
measure the voltage over the temperature sensor.
The measured voltage has a linear relationship to the temperature as described in
The sensitivity is approximately 1 LSB /
ibration. Typically, the measurement accuracy after a single temperature calibration is ±
assuming calibration at room temperature. Better accuracies are achieved by using two
temperature points for calibration.
Table 16-2.
The values described in
temperature 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 soft-
ware. The sofware calibration can be done using the formula:
where ADCH and ADCL are the ADC data registers, k is the fixed slope coefficient and T
temperature sensor offset. Typically, k is very close to 1.0 and in single-point calibration the
coefficient may be omitted. Where higher accuracy is required the slope coefficient should be
evaluated based on measurements at two temperatures.
Temperature
ADC
T = k * [(ADCH << 8) | ADCL] + T
Temperature vs. Sensor Output Voltage (Typical Case)
Table 16-2
230 LSB
-40 °C
are typical values. However, due to process variation the
°
C and the accuracy depends on the method of user cal-
OS
300 LSB
+25 °C
370 LSB
+85 °C
8006G–AVR–01/08
Table 16-2
OS
10°
is the
C,