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Design Considerations for Measuring Ambient Air Temperature (Rev. B)


Power-hungry electronic components such as processor chips, field programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), as well as power ICs heat up during operation. When the system is turned on, the heat generated by these ICs transfers to lower temperature objects nearby. Measuring ambient air temperature with a surface mount device can be challenging because heat transfer from components on the same PCB can influence and interfere with the ambient air temperature reading of the sensor. To maintain accuracy in applications that require ambient air temperature measurement, it is important to follow good layout techniques such as understanding the dominant thermal path, isolating the island surrounded by the package, and keeping the device as far away from interfering heat sources as possible. This application note will focus on layout strategies to overcome off-board (ambient air) temperature sensing challenges encompassing many applications. It details recommended layout techniques for accurate measurement of ambient air temperature with a temperature sensor in a plastic package, such as the TMP116 or TMP117. The application note includes measurement data of the TMP116 ambient air temperature measurement, and the LMT70 which is used as a reference to the temperature sensor to distinguish between air temperature measurement and the interference from a nearby heat source.