RFM22B/23B
8.4. Temperature Sensor
An integrated on-chip analog temperature sensor is available. The temperature sensor will be automatically
enabled when the temperature sensor is selected as the input of the ADC or when the analog temp voltage is
selected on the analog test bus. The temperature sensor value may be digitized using the general-purpose ADC
and read out over the SPI through "Register 10h. ADC Sensor Amplifier Offset." The range of the temperature
sensor is configurable. Table 16 lists the settings for the different temperature ranges and performance.
To use the Temp Sensor:
1. Set the input for ADC to the temperature sensor, "Register 0Fh. ADC Configuration"—adcsel[2:0] = 000
2. Set the reference for ADC, "Register 0Fh. ADC Configuration"—adcref[1:0] = 00
3. Set the temperature range for ADC, "Register 12h. Temperature Sensor Calibration"—tsrange[1:0]
4. Set entsoffs = 1, "Register 12h. Temperature Sensor Calibration"
5. Trigger ADC reading, "Register 0Fh. ADC Configuration"—adcstart = 1
6. Read temperature value—Read contents of "Register 11h. ADC Value"
D7
D6
D5
D4
D3
D2
D1
D0
POR Def.
Add R/W Function/Description
tsrange[1]
tsrange[0] entsoffs entstrim
tstrim[3]
tstrim[2] vbgtrim[1] vbgtrim[0]
12 R/W
Temperature
20h
Sensor Control
tvoffs[7]
tvoffs[6]
tvoffs[5] tvoffs[4]
tvoffs[3]
tvoffs[2]
tvoffs[1]
tvoffs[0]
13 R/W Temperature Value Offset
00h
Table 16. Temperature Sensor Range
entoff
tsrange[1]
tsrange[0]
Temp. range Unit
Slope
ADC8 LSB
0.5 °C
1 °C
1
1
0
0
1
1
1
0
1
0
1
0
–64 … 64
–64 … 192
0 … 128
°C
°C
°C
°F
°K
8 mV/°C
4 mV/°C
8 mV/°C
4 mV/°F
3 mV/°K
1
0.5 °C
1 °F
1
–40 … 216
0 … 341
0*
1.333 °K
*Note: Absolute temperature mode, no temperature shift. This mode is only for test purposes. POR value of
EN_TOFF is 1.
The slope of the temperature sensor is very linear and monotonic. For absolute accuracy better than 10 °C
calibration is necessary. The temperature sensor may be calibrated by setting entsoffs = 1 in “Register 12h.
Temperature Sensor Control” and setting the offset with the tvoffs[7:0] bits in “Register 13h. Temperature Value
Offset.” This method adds a positive offset digitally to the ADC value that is read in “Register 11h. ADC Value.” The
other method of calibration is to use the tstrim which compensates the analog circuit. This is done by setting
entstrim = 1 and using the tstrim[2:0] bits to offset the temperature in “Register 12h. Temperature Sensor Control.”
With this method of calibration, a negative offset may be achieved. With both methods of calibration better than
±3 °C absolute accuracy may be achieved.
The different ranges for the temperature sensor and ADC8 are demonstrated in Figure 28. 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.
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