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TMP275: Layout suggestions and placement of TMP275 for accurate temperature measurement..

Dhara Pandya
Expert 1220 points
Part Number: TMP275

Hi,

I want to use TMP275 IC for measuring temperature at different location on the surface of a test set-up.

What points should I take care when I am designing the layout using this IC for accurate temperature measurement..?
Should I do 'copper pouring' connecting the package of this IC or should I connect ground pin of this IC with copper pour..??

Pls. let me know if any one can help with this..

Thanks in advance..

Dhara

  • 0
    TI__Mastermind 35825 points
    Hi Dhara,

    What are you trying to measure? Generally speaking, you want to make good thermal contact with the measured object. Metals have good thermal conductivity, so they can be used to make a thermal connection. Thermal grease or thermally-conductive epoxies can also be used to make a thermal connection. When using metal to make a thermal connection, be careful not to make an undesired electrical connection as well!

    The metal leads of the package have the best thermal conductivity to the sensor inside. Inside the molded package, the semiconductor device sits on a metal flag. In some packages, this metal flag has a metal connection to the bottom of the package. TMP275 does not feature this type of package.

    Since metal has good thermal conductivity, copper pour can be used to make thermal connection to the area beneath the package. There will still be some amount of thermal resistance between this metal, the plastic molded package, and the sensor inside. This thermal resistance is called RθJC(bot) and is found in Specifications section of the datasheet.

    Depending on physical constraints of your application, you may also directly contact the measured object with the top of the molded package. There will still be some thermal resistance between the top of the package and the sensor inside. This thermal resistance is called RθJC(top) and is found in Specifications section of the datasheet.

    Without a thermal connection to anything in particular, the sensor will have a specified thermal resistance to the ambient air temperature. If your goal is to measure ambient temperature, you'll notice that this resistance is relatively high. Therefore, it is important to thoroughly isolate the device from other thermal connections, so that the ambient thermal resistance dominates.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    Expert 1220 points
    Hi Ren,


    Many thanks for the detailed explanation.. Its of a great help to me..

    I want to measure the temperature of one of the test set-up at 5 different locations and need to program for specific action on detection of a certain cut-off temperature limit..

    I have chosen TMP275 for measuring the temperature and right now designing the hardware for the same.. Which will be a small PCB of 14mm X 17mm size which I can mount at the required location.

    Hence needed to know any important points to consider to design the PCB for efficient contact between IC and the test set-up body for accurate measurement of temperature.

    I referred the datasheet of TMP275 for RθJC(top) and RθJC(bot) values.. After which I presume that for measuring the temperature accurately I will have to mount the IC's top surface with the test set-up body..

    Let me know your suggestions if any regarding this..



    Thanks & Regards,

    Dhara Pandya.
  • 0 in reply to Dhara Pandya
    Expert 1220 points
    Hi Ren,

    One more query regarding the TMP275 PCB design..

    As mentioned on the TMP275 datasheet page 23, I will have to connect the Gnd Pin (Pin No.4) with copper pouring..??

    And in this case, I will still have to mount this PCB with the Top of the IC with measured body..?? or with bottom of PCB with measured body..??

    Pls. advice regarding this..


    Thanks..
    Dhara Pandya.
  • 0 in reply to Dhara Pandya
    TI__Mastermind 35825 points
    Hi Dhara,

    Page 23 shows an example of a thermal connection using copper pour. You should decide which thermal connection is best for your application, and remove all other thermal connections. If you would like to directly contact the top of the package, then you should not use any copper pour on the PCB.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    Expert 1220 points
    Hi Ren,

    Thankyou for the advice..


    Regards,
    Dhara