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I have a KP236N6165XTMA1 5V analog pressure sensor and a SHT31-ARP-B 3.3V analog temperature and humidity sensor on the same circuit, connected to the same ground plane (see v0.2 schematic bellow).

enter image description here

The layout on my PCB looks like this (this is v0.1 which I have been testing on, it had its 3.3V power coming from the connector with an additional pin, but in v0.2 seen in the schematic above, the 5V will be converted to 3.3V directly on the circuit):

enter image description here

If I power both sensors, the temperature and humidity analog outputs are incorrect. For example, the temperature readings are 5-6 degrees celsius (+0.3V) above what they should be.

When I remove the ESD diodes and only power the 3.3V, the 3.3V temperature and humidity sensor gives correct analog outputs, measuring around 20 degrees celsius which is indeed the room's temperature.

When I power back the 5V pin, and thereby the 5V pressure sensor, my temperature readings incrementally increase in the next couple of seconds, reaching 25 or 26 degrees celsius. They then go back to normal readings when I disconnect the 5V.

What could this shift be due to? Is my grounding incorrect? Could my signals be interfering with something? Could there be leakage current from somewhere?

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1 Answer 1

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What could this shift be due to? Is my grounding incorrect? Could my signals be interfering with something? Could there be leakage current from somewhere?

The pressure sensor draws about 8 mA from the 5 volt supply. That's a power of 40 mW that will heat the surrounding circuits. That is what I believe is heating-up the circuit board and affecting the temperature reading from your temperature sensor.

You could try and prove this by drawing heat away from the pressure sensor if it's possible to attach a heatsink or, just use an external temperature probe to measure it. Or, remove the pressure sensor chip and test the remaining items on the PCB with and the 5 volts connected.

You could even test the pressure sensor on its own (in air) and see how warm it gets without having the PCB thermally remove heat.

You only have a tiny PCB so it can easily rise in temperature even for a few tens of milliwatts.

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  • \$\begingroup\$ If this hypothesis is correct, one solution could be to switch off the pressure sensor except when reading the pressure. The datasheet shows powerup characteristics of the sensor, so it appears that the manufacturer expects that the pressure sensor will be used in this fashion. \$\endgroup\$
    – elchambro
    Commented Dec 19, 2023 at 23:51
  • \$\begingroup\$ Thanks a lot for your answer Andy. I had thought about it but refused to believe it for such low power. Would the heat be conducted more through the air or through the copper in your opinion? A heat sink could work for the buck converter but wouldn't work optimally for the pressure sensor which has a plastic case. Could another solution involve connecting the sensors' ground planes at a single point near the connector or buck converter's ground? How about inserting a laser cut gap between the sensors? \$\endgroup\$
    – Tommy95
    Commented Dec 20, 2023 at 9:24
  • \$\begingroup\$ Thanks @elchambro, unfortunately it takes about a minute for the temperature reading to stabilize after powering the pressure sensor, so it wouldn't be very reactive. In addition, I only have 5 pins in the industrial connector I want to use and all of them are already used (5V, GND, T, P, H) \$\endgroup\$
    – Tommy95
    Commented Dec 20, 2023 at 9:27
  • \$\begingroup\$ @Tommy95 if we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification. \$\endgroup\$
    – Andy aka
    Commented Dec 20, 2023 at 9:33
  • \$\begingroup\$ Andy, I still need to test this hypothesis, I will try to do it tonight \$\endgroup\$
    – Tommy95
    Commented Dec 20, 2023 at 16:30

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