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TMP117: TMP117 packaging and installation practice

Part Number: TMP117

I am going to use TMP117 on my PCB design inside a package. 

I noticed there are several sources of temperature error I have to remove to be able to gain the sub-degrees accuracy of TMP117. 

1- Sun light emitting on the package will increase the temperature readings

2- Sensor mounted inside the package will have a temperature offset of about 10 degrees higher than outside in a hot environment

3- PCB layout and outline around the temperature sensor can impact the readings specially if hot components such as MCUs are sharing ground planes with the temp sensor. 

I am sure there could be other sources of error that I may have not noticed than the ones listed above. 

Now my question is, what is the general practice for PCB layout and outline design, sensor packaging, and etc. that can be used so that I can gain 0.1 degrees accuracy of TMP117 sensor I use and minimize all sources of temperature induced errors. 

I appreciate if you advise or refer to an app. note from TI about this. 

Thanks

  • Hi Kaveh,

    Thank you for posting to the Sensing forum.

    The first step to designing a system for accurate ambient temperature measurements is understanding the thermal path of the enclosure. I recommend placing the TMP117 near an external vent if possible, away from the main MCU. The following Layout Considerations for Accurately Measuring Ambient Temperature application report goes into more detail on these recommended layout practices. 

    In addition to the considerations you have already pointed out, placing cutouts or perforations around the TMP117 will help reduce the thermal mass of board surrounding the sensor and will minimize heat transfer from other components. 

    Additional resource: Design Considerations for Measuring Ambient Air Temperature application report

    Best regards,

    Nicole

  • Thanks Nicole, 

    What is "Thermal Path of enclosure"? 

    I am worried about the sensor being inside the package and that increases temperature error significantly. Can I expose the sensor to outside fresh air? What materials could be used for sealing the pins that would have no impact on the temperature measurement. How should the packaging look like around the sensor? Do you have any data to share about this? 

    Thanks 

  • Hi Kaveh,

    For best ambient temperature measurements the sensor should be placed in the enclosure so that there is a path of airflow to the device, as seen in the application report I linked previously:

    It is fine to expose the sensor to outside air. To further protect the sensor and board from the environment, a conformal coating may be used. I am not aware of any specific requirements for coating the TMP117, and a standard conformal coat should be fine.

    Best regards,
    Nicole