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TMP117: Temperature sensing location

Dennis Ryu
Prodigy 80 points
Part Number: TMP117

Hello,

Within the TMP117, where would the actual temperature sensing location be?

Would it be at the top of the IC package, or towards the bottom of the IC package?

And does this differ between the WSON and BGA models?

Thank you.

  • 0
    TI__Expert 4810 points

    Hello Dennis,


    Unfortunately, we would not be able to share details in regards to the location of the sensing element as that is proprietary information. Please let us know if you have any other questions.


    Regards,

    Harry 

  • 0 in reply to HarryG
    Prodigy 80 points

    Hello Harry,

    Thank you for the response!

    We are inquiring as we are contemplating what the best implementation of the TMP117 would be on our PCB.  We are using this IC for skin temperature acquisition, but are wondering whether we should place the IC on the top layer or the bottom layer.  For the most efficient thermal transfer to the PCB and IC, where should we connect the thermal path?  We are also considering using a heat transfer epoxy.

    Thank you.

  • 0 in reply to Dennis Ryu
    TI__Expert 4810 points

    Hello Dennis,

    Getting the IC as close to the skin as possible would be the best recommendation and I would also suggest avoiding the YBG package variant for such use. 

    I would also suggest the following documents for additional information in regards to designing a wearable: Design Considerations for a Wearable Temperature Monitoring System and Layout Considerations for Wearable Temperature Sensing.

    Hope this helps,

    Harry

  • 0 in reply to HarryG
    Prodigy 80 points

    Hello Harry,

    Thank you so much for the feedback.  This is very helpful!

    We resorted to the BGA package due to size constraints of the PCB.  How much of a noticeable impact on temperature acquisition / response time do you anticipate for the BGA vs. WSON?  Would this data be available?

    I noticed the documents you sent also refer to the WSON package instead of the BGA.  Would you say the BGA component would not be a viable choice for skin temperature measurement purposes?

    Thank you.

  • 0 in reply to Dennis Ryu
    TI__Expert 4810 points

    Hello Dennis,


    Understood. We currently don't have any data available comparing the response times for these packages (specifically for the 117). That being said, since the BGA is a smaller package, it will have a lower thermal mass, hence a better response time than the WSON. I also wanted to let you know we might have some collateral available soon which will provide some more information and clarity on this.

    As for the package, BGA should prove a better choice for skin measurement as mentioned (better response time). If this device is being placed on an FPC, I would also suggest adding stiffener to the portion where the device will be placed to reinforce it without impacting response just as a precaution.

    Additionally, I would also suggest taking a look at Section 8.2.2.2 of the datasheet (page 34) regarding the self-heating effect to ensure you get the best possible measurements.

    Lastly, if accuracy is a priority for your design, I would recommend the newer TMP119, which is a drop-in replacement for the TMP117 and also available in a BGA package. It has a higher accuracy of 0.08*C.

    Hope this helps!

    Harry