Manual

RF22
Version: 0.1 Date: 12/23/2008
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38
Bit D7 D6 D5 D4 D3 D2 D1 D0
Name tsrange[1:0] entoff envbgcal vbgcal[3:0]
Type R/W R/W R/W R/W
Reset value = 00100000
Bit Name Function
7:6 tsrange[1:0] Temperature Sensor Range Selection.
(FS range is 0..1024 mV)
00: –64
o
C~64
o
C (full operating range), with 0.5
o
C resolution (1 LSB in the 8 bit ADC)
01: –64
o
C ~192
o
C, with 1
o
C resolution (1 LSB in the 8 bit ADC)
11: 0
o
C~128
o
C, with 0.5
o
C resolution (1 LSB in the 8 bit ADC)
10: –40
o
F~216
o
F, with 1
o
F resolution (1 LSB in the 8 bit ADC)
5 entoff Temperature Sensor Offset Enable.
4 envbgcal Temperature Sensor Calibration Enable.
3:0 vbgcal[3:0] Temperature Sensor Calibration Value.
Table23. Temperature Sensor Range
entoff tsrange[1] tsrange[0] Temp. range Unit Slope ADC8 LSB
1 0 0 –64 … 64 °C 8 mV/°C 0.5 °C
1 0 1 –64 … 192 °C 4 mV/°C 1 °C
1 1 0 0 … 128 °C 8 mV/°C 0.5 °C
1 1 1 –40 … 216 °F 4 mV/°F 1 °F
0* 1 0 0 … 341 °K 3 mV/°K 1.333 °K
*Note: Absolute temperature mode, no temperature shift. This mode is only for test purposes. POR value of EN_TOFF is 1.
Control to adjust the temperature sensor accuracy is available by adjusting the bandgap voltage. By enabling the
envbgcal and using the vbgcal[3:0] bits to trim the bandgap the temperature sensor accuracy may be fine tuned in the
final application. The slope of the temperature sensor is very linear and monotonic but the exact accuracy or offset in
temperature is difficult to control better than ±10 °C. With the vbgtrim or bandgap trim though the initial temperature
offset can be easily adjusted and be better than ±3 °C.
The different ranges for the temperature sensor and ADC8 are demonstrated in Figure 26. The value of the ADC8 may
be translated to a temperature reading by ADC8Value x ADC8 LSB + Lowest Temperature in Temp Range. For
instance for a tsrange = 00, Temp = ADC8Value x 0.5 – 64.
Temperature Measurement with ADC8
0
ADC value
Sensor Range 3
Sensor Range 2
Sensor Range 1
Sensor Range 0
Temperature [Celsius]
80 100200-20
100
150
200
250
300
-40
50
40 60
Figure26. Temperature Ranges using ADC8