Datasheet

192
7734Q–AVR–02/12
AT90PWM81/161
Figure 15-2. Illustration of Vbg as a function of temperature.
15.4 Temperature Measurement
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC12 channel, as shown on Figure 15-3.
Figure 15-3. Temperature sensor circuitry.
Selecting the ADC12 channel by writing the MUX3..0 bits in ADMUX register to “1100” enables
the temperature sensor (see “ADMUX - ADC Multiplexer Register” on page 217). The recom-
mended ADC voltage reference source is the internal 2.56V voltage reference for temperature
sensor measurement. When the temperature sensor is enabled, the ADC converter can be used
in single conversion mode to measure the voltage over the temperature sensor. The amplifier
allows to charge the ADC sample capacitor at full CKadc clock speed. The measured voltage
has a linear relationship to temperature as described in Table 15-1 on page 193. When the volt-
age reference equals 2.56V, the conversion result has approximately a 1LSB/°C (or 2.5mV/°C)
Temperature (°C)
1.0
Temperature range of interest
-20
1.5
0.5
-40
BGCRR is used to move the top of the Vbg curve to the
center of the temperature range of interest
4020-0 1008060
VPTAT
ADC Mux=1100
Current-voltage
Convertor
BG Reference
Enable when
ADEN=1
Enable when
ADC Mux=1100
Vtemp+
-