TMP117 datasheet(32/45 Pages) TI1

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Die

Package

Bond Wire

Epoxy

Exposed Pad

Heat Flow

TMP117

SNOSD82 – JUNE 2018

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Application Information (continued)

8.1.1.2 Detailed Design Procedure

8.1.1.2.1

TMP117 Design Procedure

The TMP117 is a local temperature sensor. Measuring a temperature point with a surface-mount device is very

challenging because of the external influence of surrounding air and other components. The TMP117 mainly

monitors the PCB temperature at the desired hotspot. To maintain accuracy in applications that requires surface

temperature measurement, follow good layout techniques (such as understanding the dominant thermal path,

isolating the island surround by the package, and keeping the distance as far as possible from the heat source).

For sensors in plastic packages (such as the TMP117 DFN device), Figure 37 shows that the die attach pad

(DAP) provides the most dominant thermal path. With the DAP, a board-mounted sensor usually does an

excellent job of measuring board temperature. The die sits on top of the metal plate leadframe with a non-

conductive die adhesive in between, allowing for a fast thermal response.

Figure 37. WSON Package Cross Section

Most power-hungry electronic components such as processor chips, field programmable gate arrays (FPGAs),

application-specific integrated circuits (ASICs), and voltage regulators heat up during operation. In order to

accurately measure the ambient temperature of a sensor in a plastic package, isolate the sensor from the heat

source using isolation island techniques and distance. TI recommends two vias per TMP117 dimension of the

thermal pad. The DAP and two vias help improve thermal characteristics. Thus, in order to take advantage of this

feature, mount the TMP117 on the board with the two copper planes on the top and bottom of the via of equal

length as the exposed die attach dimension. The bottom plane contains the temperature sensing elements. In

order to achieve the fast temperature response, the mini board dimension must be enough to accommodate the

TMP117 and the bypass capacitor with the isolation air gap to prevent the heat source dissipated to the mini sub-

board.

8.1.1.2.2

Noise and Averaging

The device temperature sampling distribution (without internal averaging) covers an area of approximately six

neighboring codes. The noise area of the six codes remains the same at full supply and full temperature range

with a standard deviation of approximately 1 LSB. The device provides an averaging tool for 8, 32, and 64

samples. As illustrated in , even the 8-sample averaging reduces the internal noise distribution to a theoretical

minimum of 2 LSB. This averaging means that if the system temperature slowly changes and the supply voltage

is stable, then the 8-sample averaging can be enough to neutralize the device noise and provide stable

temperature readings. However, if the system temperature is noisy (such as when measuring air flow

temperatures), than higher averaging numbers are recommended to be used.

TMP117 Datasheet(PDF) 32 Page - Texas Instruments

TMP117 Datasheet(HTML) 32 Page - Texas Instruments

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