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TMP112 Questions

Luis Filipe Rossi
Expert 1035 points
Other Parts Discussed in Thread: TMP112

Hi, i am planning on using TMP112 for temperature measurent, but i have a few questions. 

The sensor will be measuring human body temperature coupled with a stainless steel. In order to themally couple the IC package should use the GND lead?Is there any way that i can thermally couple it but still keep it isolated?

Second question is about accuracy and power. The final device will be battery powered (CR2032 for instance). What is the best way to improve accuracy? Directly power from the battery (with the apropriate bypass capacitor) or use an LDO to get a more stable power rail? The reason of my question is that with lower voltage the sensor will decrease the accuracy, but i am afraid the slowing decreasing voltage of the battery will be worst.

Thank you!

  • 0
    TI__Mastermind 18415 points

    Luis,

    I am currently looking into this and will get back to you soon. 

  • 0 in reply to Chris Featherstone
    Expert 1035 points

    Thank you very much. Will be waiting.

    Regards, 

    Luís Filipe Rossi

  • 0
    TI__Mastermind 18415 points

    Luis,

    From your description it sound like the stainless steel will be warmed up by the human body and you will thermally connect the TMP112 to the stainless steel in order to measure the temperature of the human body.

    I am going to suggest an RTD for your design. This is because you will have the ability to couple the RTD directly to the skin and measure temperature very accurately. Relying on the thermodynamic properties of the stainless steel to provide an accurate representation of the body temperature will ultimately throw off the temperature accuracy which you are looking to improve.

    In your design, is it possible to use an RTD such as the PT100. Here is a link to this device: http://www.thermometricscorp.com/rtdsensors.html. This RTD offers very good accuracy over the temperature range from T = -200 to +850 degC. The temperature range is overkill for your design however the benefits of using this device are worth noting.

    In order to interface the RTD to a micro-controller I would recommend looking at the ADS1247. This analog to digital converter can interface with a microcontroller and provides a complete front-end solution for temperature sensor applications including RTDs. 

    Here is a link to the ADS1247 : http://www.ti.com/product/ads1247

    Under tools and software you will find an IBIS model that you can use to simulate your system using Texas Instruments free SPICE simulator TINA. Here is a link to the TINA users guide. 

    TINA: http://www.ti.com/tool/tina-ti&DCMP=hpa_amp_general&HQS=Other+OT+tina-ti

    If you scroll down to the bottom of the page you will see the download tab for TINA. If you would like to test out the device you can order a free sample from theADS1247 link above. We also have an evaluation module available for purchase that can help out with prototyping your system.


  • 0 in reply to Chris Featherstone
    Expert 1035 points

    Hi. The way that the temperature sensor is coupled to the body is not an option. The final device is an actimeter, and the formfactor is a watch. You usually measure the temperature with stainless steel that goes in contact with the wrist. The accuracy should be something around 0.5ºC or a bit less. Other option i got is to go for thermistor but i would rather prefer an IC temperature sensor. Any comment on the best way to connect the TMP112 to the steel and about the power rail? I am considering usinga boost converter to get the most i can from the battery, but the coupling question is still something i would need, even for other projects.

    Thank you for your help and tim!

  • 0 in reply to Luis Filipe Rossi
    TI__Mastermind 18415 points

    Luis,

    The best way to connect the TMP112 to the steel is going to be with a ground pin connection. This will provide the most accurate reading because the pins of the device provide the best thermal path to the die of the TMP112. 

  • 0 in reply to Chris Featherstone
    Prodigy 105 points

    Hi Chris

     

    The direct contact between steel and GND of TMP112 is good for thermal conduct. Would you advise on ESD performance?

     

    Regards

    Alex

  • 0 in reply to alex xu2
    TI__Genius 15760 points

    Hi Alex,

    Please see my reply on:

    http://e2e.ti.com/support/other_analog/temperature_sensors/f/243/t/356577.aspx

    Mayrim