ATTINY861A-SU Atmel, ATTINY861A-SU Datasheet - Page 152

• Manufacturer Part Number: ATTINY861A-SU
• Description: IC, MCU, 8BIT, 8K FLASH, 20SOIC
• Manufacturer: Atmel

Specifications of ATTINY861A-SU

• Controller Family/series: ATtiny
• No. Of I/o's: 16
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 512Byte
• Cpu Speed: 20MHz
• No.: RoHS Compliant
• Core Size: 8bit
• Program Memory Size: 8KB
• Oscillator Type: External, Internal
• Rohs Compliant: Yes

15.12 Temperature Measurement
152
ATtiny261A/461A/861A
where V
and V
0x200 (-512d) through 0x000 (+0d) to 0x1FF (+511d). The GAIN is either 1x, 8x, 20x or 32x.
However, if the signal is not bipolar by nature (9 bits + sign as the 10th bit), this scheme loses
one bit of the converter dynamic range. Then, if the user wants to perform the conversion with
the maximum dynamic range, the user can perform a quick polarity check of the result and use
the unipolar differential conversion with selectable differential input pair. When the polarity check
is performed, it is sufficient to read the MSB of the result (ADC9 in ADCH). If the bit is one, the
result is negative, and if this bit is zero, the result is positive.
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC11 channel. Selecting the ADC11 channel by writing the MUX5:0 bits in
ADMUX register to “111111” enables the temperature sensor. The internal 1.1V voltage refer-
ence must also be selected for the ADC voltage reference source in the temperature sensor
measurement. When the temperature sensor is enabled, the ADC converter can be used in sin-
gle 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 15-2.
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
the 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
REF
POS
the selected voltage reference. The result is presented in two’s complement form, from
is the voltage on the positive input pin, V
Temperature vs. Sensor Output Voltage (Typical Case)
Table 15-2
ADC
230 LSB
-40 °C
=
are typical values. However, due to process variation the
(
---------------------------------------------------- - GAIN
V
POS
°
C and the accuracy depends on the method of user cal-
OS
–
V
V
REF
NEG
) 512
⋅
NEG
300 LSB
+25 °C
⋅
the voltage on the negative input pin,
370 LSB
+85 °C
8197B–AVR–01/10
Table 15-2
10°
OS
C,
is