John,
From your question, I am assuming you are wanting an accurate temperature measurement, so please note that the internal TEMP SENSOR in the CC2540 is not for this purpose, it will only give an estimated temperature. For more accurate measurements, there is an input to the on-chip ADC that can be used with an external temp sensor.
For either implementation, please read the CC2540 User Guide, starting with Section 13.2:http://www.ti.com/litv/pdf/swru191d . From section 13.2:
13.2 Using the Battery Monitor for Temperature Monitoring
The battery monitor can also be used to do some simple temperature monitoring. When the battery monitor is connected to the internal temperature sensor instead of the supply voltage AVDD5 (see the description of MONMUX in Section 13.3), it can indicate whether the temperature is above or below a certain level. This is done by comparing the voltage coming from the temperature sensor to the voltage trigger point of the battery monitor. The controls for this measurement are the same as for the normal use of the battery monitor (see the description of BATTMON in Section 13.3). It is important to understand that due to the nature of the battery monitor (optimized for voltages arround 2V) and the output voltage range of the temperature sensor, there are only about 8 temperature trigger values in the temperature range of –40°C to 125°C (see Table 13-1). As a result, the battery monitor gives only a rough indication of the temperature range, but this is useful for doing temperature compensation on analog components in a system. See the device's data sheet (Appendix C) for performance characteristics details.
Table 13-1. Values Showing How Different Temperatures Relate to BATTMON_VOLTAGE for a Typical Device
Temperature BATTMON_VOLTAGE
-40°C 22
-26°C 21
-11°C 20
7°C 19
25°C 18
47°C 17
70°C 16
97°C 15
128°C 14
The temperature sensor is inversely proportional to BATTMON_VOLTAGE. The temperature (in °C) corresponding to a given BATTMON_VOLTAGE is given by:
TEMP = [ (A) / BATTMON_VOLTAGE<4:0>] – B
-Leonard
Analog Applications - ACAT Dallas