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TMP236: Thermal design of TMP235/236 series temperature sensor

Tony Zhang
Prodigy 205 points
Part Number: TMP236
Other Parts Discussed in Thread: TMP235, ISOTMP35

Tool/software:

Dear Friend

My application is to protect a linear Mosfet from overheating with possible heavy/overstressed usage.  the Mosfet is surface mounted with its drain connected to a piece of copper on top of PCB. My plan is to mount the TMP236A2DCKR near the Mosfet with its body glued on the same piece of copper by Kafuter K-5204K Silicone Adhesive Paste.  My questions are:

1. Is my plan good enough for the sensor to sense the true case temperature of the Mosfet?

2. Should/Can I connect pin1 and pin5 of the TMP236 to the same piece of copper?

3. Any other better thermal design in such applications?

 

Best Regards

Tony

  • 0
    TI__Expert 8065 points

    Hi Tony,

    What voltage will your MOSFET be at? Other than the thermal paste connection for the TMP236 package body, will it be electrically connected to the copper in any way?

    I would only connect pins 1 and 5 of the TMP236 to a copper pad if that pad is grounded, otherwise they should be left floating.

    Regards

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 205 points

    Hi Alex

    The voltage applied to the MOSFET's drain is specified at 30V max. 

    If pin1 and pin5 of the TMP236 can only be connected to GND (pin2),  there will be no pins electrically connected to the copper of interest.

    So, it seems the only thermal path will be the body of TMP236 being glued to the copper of interest. Is it good enough?

    In such case, what will be the estimated thermal resistance of TMP236's body for calculation of MOSFET case temperature via TMP236's output data?

    Best Regards

    Tony

  • 0 in reply to Tony Zhang
    TI__Expert 8065 points

    Hi Tony,

    Thanks for letting me know the MOSFET drain voltage, I definitely would not connect any pin of the TMP235 to 30V.

    If you are interested in a different device, I would like to recommend our ISOTMP35, which is an isolated analog temperature. The ISOTMP35 uses the TMP235 die in an isolated package, which has a slightly different gain and offset than the TMP236 but is very similar otherwise. I think the ISOTMP35 would be a good fit for your application because the ISOTMP35 is designed to directly connect to high voltage FETs, heatsinks, bus bars, and copper pads that a normal temp sensor could not directly connect to. Here is an example of what I have in mind:

    As you can see in this example, the ISOTMP35 directly connects to the MOSFET, without the need for thermal epoxy. The ISOTMP35 has a working voltage rating of 700V DC, so it will more than enough isolation for your application. The main advantage of the direct connection is you will see a much faster thermal response with direct metal connection than using a thermal epoxy between the package body of the TMP236 and the copper.

    if you still want to go with TMP236, the thermal resistance information is in the datasheet (you need the junction to board thermal resistance):

    Regards

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 205 points

    Hi Alex

    Thank you for the recommendation.

    ISOTMP35 is great and I had noticed it when searching sensors. unfortunately, I also found no place to buy it, even just 10 pieces for prototyping.

    It is not available from either TI or distributors such as Mouser/RS components. Do you know where I can buy it from?

    Thank you.

    Tony

  • 0 in reply to Tony Zhang
    TI__Expert 8065 points

    Hi Tony,

    The ISOTMP35 was only released to market about a month ago, so it may not have been fully released and available when you looked. If you look at the automotive grade product page (https://www.ti.com/product/ISOTMP35-Q1), I see that there over 7000 in stock currently. So you should be able to buy it from TI.com.

    I hope this helps.

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 205 points

    Hi Alex

    Thank you for the information.

    However, the order page shows "out of stock". 

     

    any help will be greatly appreciated.

    Best Regards

    Tony

  • 0 in reply to Tony Zhang
    TI__Expert 8065 points

    Hi Tony,

    Do you have a TI account? Please create one if you don't and log in, I confirmed that we have several thousand in stock for purchase on the TI.com store.

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 205 points

    Hi Alex

    Do you mean "myTI" account? I have one, otherwise, I won't be able to post a question here.

    I have purchased other parts from the account login.  but this part is "out of stock".

    May be the stock is not yet opened for order.

    Best Regards

    Tony

  • 0 in reply to Tony Zhang
    TI__Expert 8065 points

    Tony,

    Thanks for bringing this to our attention. I am working with our marketing team to get this issue resolved. I will update the thread on Monday when I know more, hopefully this is resolved by then

    Thank you

    -Alex Thompson

  • 0 in reply to Alex Thompson
    TI__Expert 8065 points

    Hi Tony,

    I haven't received word that this has been resolved yet, but we have identified the issue and our sales team should resolve it shortly. I will respond back on the thread once I have confirmation that you should be able to see the ISOTMP35 inventory.

    Thank you for your patience.

    Regards

    -Alex Thompson

  • 0 in reply to Alex Thompson
    TI__Expert 8065 points

    Tony,

    I received word from our sales team that you should now be able to purchase the ISOTMP35 from TI.com, please confirm if you can do so.

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 205 points

    Hi Alex

    Yes, I can see the inventory and place an order for it.

    Thank you so much for the help.

    Tony 

  • 0 in reply to Tony Zhang
    TI__Expert 8065 points

    Tony,

    Fantastic, glad I could help. Please reach out again on E2E if you have questions about using ISOTMP35.

    Regards

    -Alex Thompson