LM3S9B81 Datasheet, PDF (508/1155 Pages) Texas Instruments – Stellaris® LM3S9B81 Microcontroller

Analog-to-Digital Converter (ADC)
13.3.6
Internal Temperature Sensor
The temperature sensor's primary purpose is to notify the system that the internal temperature is
too high or low for reliable operation.
The temperature sensor does not have a separate enable, because it also contains the bandgap
reference and must always be enabled. The reference is supplied to other analog modules; not just
the ADC.
The internal temperature sensor provides an analog temperature reading as well as a reference
voltage. The voltage at the output terminal SENSO is given by the following equation:
SENSO = 2.7 - ((T + 55) / 75)
This relation is shown in Figure 13-11 on page 508.
Figure 13-11. Internal Temperature Sensor Characteristic
Sensor = 2.7 V – ^(T+55)
75
Sensor
2.7 V
1.633 V
0.3 V
-55° C
25° C
125° C Temp
13.3.7
The temperature reading from the temperature sensor can also be given as a function of the ADC
value. The following formula calculates temperature (in ℃) based on the ADC reading:
Temperature = 147.5 - ((225 × ADC) / 1023)
Digital Comparator Unit
An ADC is commonly used to sample an external signal and to monitor its value to ensure that it
remains in a given range. To automate this monitoring procedure and reduce the amount of processor
overhead that is required, 16 digital comparators are provided. Conversions from the ADC that are
sent to the digital comparators are compared against the user programmable limits in the ADC
Digital Comparator Range (ADCDCCMPn) registers. If the observed signal moves out of the
acceptable range, a processor interrupt can be generated. The digital comparators four operational
508
June 29, 2010
Texas Instruments-Advance Information