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TMP451 output temperature maintain 115 degree when ambient temperate increasing over 125 degree

user4411814
Prodigy 160 points
Other Parts Discussed in Thread: TMP451

hello

       l am use ti TMP451 to monitor our MCU;TMP451 output temperature maintain 115 degree when ambient temperate increasing over 125 degree;

I need my device pass the high temperature test; what`s reason  case this problem?

  • 0
    TI__Expert 4905 points

    Hi,

    What MCU are you using?

    How are you measuring it's temperature?

    How are you verifying that the temperature is indeed increasing?

    Here is some guidance from the TMP451 data sheet:

    If a discrete transistor is used as the remote temperature sensor with the TMP451, the best accuracy can be

    achieved by selecting the transistor according to the following criteria:

    1. Base-emitter voltage > 0.25 V at 7.5 μA, at the highest sensed temperature.

    2. Base-emitter voltage < 0.95 V at 120 μA, at the lowest sensed temperature.

    3. Base resistance < 100 Ω.

    4. Tight control of VBE characteristics indicated by small variations in hFE (that is, 50 to 150).

    Based on this criteria, two recommended small-signal transistors are the 2N3904 (NPN) or 2N3906 (PNP).

    Take care,

  • 0 in reply to Emmy Denton
    Prodigy 160 points

    Dear emmy

        thank your for your help,about the transistor: l tested our transistor voltage in different current ;it match the criteria 1 and 2;

    the plot is as follows:  the top is be voltage in 120ua ; the blow is be voltage in 7.5uA;

    about the criteria 4 how to verify it?

  • 0 in reply to user4411814
    TI__Expert 4905 points
    Hi again,

    Glad you were able to verify criteria 1 and 2 and actually provide us with a curve!

    Why are there three curves for each current level - what to they represent?

    For criteria number 4 - is this an integrated diode (in an ASIC, FPGA or other device)?

    If it is it's probably a vertical PNP transistor structure with is collector tied to the substrate of the IC. You can easily measure the beta of the transistor in question easily using a curve tracer. But - that will not give you the process spread, so I would recommend that ask the manufacturer of the device that includes the thermal diode to tell you. If that is you then you will need to actually measure enough devices to ensure you covered your process variation. Perhaps someone in your process/modeling team can help you.


    Can you describe to me your test setup that you use to measure the temperature of your MCU?

    How do you change the temperature from 115C to 125C?

    Can you send me your schematic?

    Thank you for your patience!

    Take care,