TMP117 datasheet(35/45 Pages) TI1

35 / 45 page

Time (seconds)

0.001

0.01

0.1

1015

-20

-10

100

110

120

Stirred Oil

Moving Air

Still Air

TMP117

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SNOSD82 – JUNE 2018

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Application Information (continued)

8.1.1.3 Application Curve

Figure 40 shows how fast the TMP117 reacts to changes in temperature. Two elements must be considered

when conducting the thermal responses experiment: the thermal conductivity and thermal mass. Thermal

conductivity is the measure of the capacity of a material (such as still air or stirred oil) to conduct heat. Thermal

conductivity is mainly used to describe how heat is conducted through a material. Higher values reflect greater

efficiency of transferring heat. A good layout technique is to keep the thermal mass as small as possible. Smaller

thermal masses result in better thermal responses.

The purpose of these experiments is to investigate how much time is required for the TMP117 temperature to

reach the set point temperature and stabilize. There are three types of tests for the thermal response: still air,

moving air, and stirred oil, as shown in Figure 40. This figure shows the step response of the TMP117 enclosed

in a chamber of still air, in a wind tunnel of moving air, and submerged in an oil bath (for the respective traces) in

a temperature environment of 70°C from room temperature (23°C). The time-constant, or the time for the output

to reach 63% of the input step is dependent on the type of test. The time-constant result depends on the PCB

and the thickness of the board that the TMP117 is mounted to. For this test, the TMP117EVM is used to perform

the thermal response. The TMP117EVM dimension is 7.6 mm × 17.8 mm with a 1-mm thickness.

Among all methods, still air has the slowest thermal response because of the enclosed box placed inside the

oven chamber without any helping elements, whereas the stirred oil experiment yields the fastest thermal

response time.

V+ = 3.3 V, tINITIAL = 23°C, tFINAL = 70°C

Figure 40. Thermal Response

TMP117 Datasheet(PDF) 35 Page - Texas Instruments