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TMP112 self heating

Bill Burris
Prodigy 135 points
Other Parts Discussed in Thread: TMP112

I'm having an issue with the TMP112 temperature sensor self heating. I have been using this part for several years in a product running at 3.3V and have not seen any self-heating issues. I recently added the TMP112 to a new design that runs at 3.1V. I'm now seeing a 3 C - 6 C increase in temperature at the sensor, from power up to about 5-6 minutes of operation in open air. The ambient temperature of the room is about 23C. when I power up the device the temperature is correct, and then it slowly increases to about 27C in 5-6 minutes. 

I used a thermo-couple on my DMM and confirmed the TMP112 is actually heating up. I have measured all the voltages on all the pins and see no issues in how it is wired. I captured the I2C communications with my scope and confirmed the MCU was reading from the TMP112 every 6 seconds and displaying the temperature.

Anyone seen this problem with the TMP112 before? 

Bill.Burris@soterawireless.com

 

  • 0
    TI__Expert 7945 points

    Hello Bill,

    I have never come across self heating issue with TMP112. Assuming you are using 10KOhms pull up on serial wires and at about 400KHz SCL clock speed you will be consuming around 33-50uWatts of power (including the current consumed during conversions). While TMP112 is sitting idle(5-6sec that you mentioned) the power consumed is much lower than this value. This could cause about 1/16-1/8degC (+/11LSB) change in temperature due to self heating effect but definitely not 3-6degC!. So, let me ask you a few questions, to make sure we get the understanding right:

    1. Whats the Pull up resistances on the SCL,SDA lines. Typical value is 10KOhms.

    2. What is your bus speed?

    3. I Know you are checking the temperature every 6 seconds, in the mean time is the device shut down or is it still converting? A good way to check this is by looking for current by hooking up an oscilloscope.

    4. What is the ALERT pin connected to? Is it connected to a power consuming LED?

    5. Is there a way for you to disconnect power to TMP112 on the board and just monitor temperature (use a thermocouple) locally to isolate the problem?

    6. Based on another interesting behavior I observed with a customer recently is that since you mentioned this was a newly designed board. Could it be that there could be some high frequency voltage signals layed out such that it is causing an electro magnetic coupling effect on the supply there by resulting TMP112's accuracies to drop 3-6degC (This is just a speculation).

    If you do not wish to disclose full details on this public forum you may also send me a schematic of your board layout  via email (abhishekmuppiri@ti.com) and I can make sure your connections are correct.

     

    Best Regards,

    Abhi Muppiri

    Applications Engineer

    AIP- Sensing Products

    Texas Instruments

  • 0 in reply to Abhishek Muppiri
    TI__Expert 7945 points

    Issue resolved: The heat from the microcontroller conducts through the power and ground planes that run under the TMP112 sensor. This causes the TMP112  to heat up 3-degC more than the actual heat sensed.