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TMP117: Design for Moving Air Measurements

Chirayu Jain
Prodigy 10 points
Part Number: TMP117
Other Parts Discussed in Thread: TMP116

Tool/software:

I am using the TMP117 to measure moving air temperature. I would like to optimize the layout of the chip and surrounding area to have the highest precision and response time for measuring the environment. In the datasheet of the TMP117 it says you should not solder the thermal pad on the IC. In SNOA986A Precise Temperature Measurements With the TMP116 and TMP117, there is an image of a layout for air temperature measurements on page 8 which shows the pcb area under the thermal pad exposed to a ground copper trace through the solder mask cut out. 

  

What is the correct layout to follow for my application? Should I have copper planes next to and under the IC with solder mask removed or not? Should the thermal pad be touching exposed copper but just not soldered? Or should the thermal pad just be isolated from the pcb altogether with solder mask covering that area?

  • 0
    TI__Genius 9610 points

    Hello Chirayu,

    When it comes to measuring ambient temperature, the key factors to keep in mind are the following:

    1) Isolation - Isolate the sensor from hot components on the PCB

    2) Reduce Thermal Mass - Reduce the PCB area around the IC - More thermal mass will increase the thermal response time

    3) Increase Thermal Conductivity - Increase the heat transfer between the air & the sensor for accuracy

    Yes, you are correct in no soldering the thermal pad. We tend to advise customers who want to measure board temperature to solder the thermal pad. Key techniques for ambient temperature measuring are shown in the following photo. A popular choice is to provide cut outs around the temperature sensor reducing the thermal mass. 

    Best Regards,

    Meredith McKean