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Part Number: TMP116
Dear TI team
I have used the tmp116 in a prototype board. It has worked as expected and compared positively with the TI EVM board. In that design the large thermal pad, underneath the chip, was left floating with few unplugged vias. Now I need to re-spin this board. The newer board will have an RF shielding can and the tmp116 has to go under. There will be a hole in the can on the top of the sensor. For this new design connecting the thermal pad to ground will simplify the board. I am wondering how that would affect the fidelity of the air temperature measurement. Naively I think that the pad being connected to the ground which is connected to the can, could be even better as the can acts as heat sink (removes the heat from the ground plane). Any thoughts advise or guidance is most appreciated. Kind regards AbderrezaK Mekkaoui
Unless your system is going to undergo a final calibration, I would not recommend soldering the thermal pad down at all. The TMP116 and TMP117 are very sensitive to mechanical stress through the thermal pad, and soldering it down can cause some loss of absolute accuracy. Section 5 of this application report does a good job summarizing the trade offs of this.
Even if the mechanical stress were not an issue I'm still not sure connecting the pad would be ideal. If the pad is connected to the ground plane then there will be a thermal path between the rest of the board and the device. So you would end up with your temperature readings being influenced by heat from other portions of your board. You're right that the can being so close and being exposed to the ambient air may help, but it's hard to predict which influence would win out.
I would recommend just leaving the TMP116 to measure air temperature via the hole in the RF shield. Provided the shield is not getting hotter than the ambient air you should get good results in terms of accuracy. If you do want to solder down the pad I'd recommend soldering it to a floating pad if possible, not to ground. You can then either do a system calibration, or try and tolerate the loss in accuracy if your application permits it.
You may be interested in checking out this app note for some more recommendations, it talks specifically about measuring air temperature with the TMP116. I hope this information is helpful, please let me know if you have any more questions.
Best Regards,Brandon Fisher
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