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CCS/TM4C1294NCPDT: Question about internal temperature sensor

Jeff zhang
Prodigy 150 points
Part Number: TM4C1294NCPDT

Tool/software: Code Composer Studio

There is an internal temperature sensor on TM4C1294. is it measuring the junction temperature of the uP? if not, what is the difference between them? and what is the thermal resistance from this sensor to the ambient?

  • 0
    TI__Guru*** 135135 points
    Hello Jeff,

    The Internal Temp Sensor is measuring the internal die temp. Not what you mean by 'what is the difference between them?'...? I don't see anything to compare the internal temperature sensor to in order to provide any differences?

    I don't see any spec for the thermal resistance, is that a requirement for you to know or just a point of curiosity?
  • 0 in reply to Ralph Jacobi
    Guru 117855 points

    Note too that "any" such: "Junction to Ambient spec" is dependent upon (additional, external considerations) - and thus a, "universal spec or measure" is (unlikely.)

    For example - here is an extract from this vendor's newer Power FET.     (a device in which such "RφJA" is of great interest/importance)    (highlight mine)

    It should be noted that the, "Supporting pcb's size, copper thickness/weight etc.", impose (serious) impact upon such specification...

    (note that "φ" was the closest symbol obtainable @ my present location)

  • 0 in reply to Ralph Jacobi
    Prodigy 150 points

    In TM4C1294 datasheet, table 30-5 provides some thermal specs:

    So, when you say the temperature sensor is measuring the die temperature, do you mean Tj (junction temperature)? If it is not the Tj, what is the difference between Tj and this temperature sensor?

    And what is the resistance from this sensor to the ambient?

    I don't see any info in the datasheet. that is why I am asking.

    Thanks

    Jeff

  • 0 in reply to Jeff zhang
    TI__Guru*** 135135 points
    Hello Jeff,

    The temperature sensor does not measure the junction temperatures, it measures the temperature of the whole die. The junction temperatures are too dependent on external factors as cb1 mentioned.

    Note that the reading is also spec'd to vary +/- 5 degrees Celsius. The ambient of course will affect it in the sense that it is the temperature of the die being measured and not a specific junction, so the environment will affect the temperature of the entire package and thus the reading.

    You may find this E2E reply and the details leading up to it useful information: e2e.ti.com/.../1528404
  • 0 in reply to Ralph Jacobi
    Guru 117855 points

    Here now - this vendor provides a graphic which nicely reveals the impact of the surrounding pcb size/geometry - upon the relationship, "Junction to Ambient."      Device shown is (again) a Power FET...

    Note that the, "Lower the value, "°C/W" the better for the semi-conductor...    (the larger pcb conductive "lands" (left drawing) are better able to draw heat from the device as compared to "minimal pcb pads."   (on the right)

    It should (now) be beyond "clear" that "external factors DOMINATE" and that poster's quest for an exacting MCU spec is, "outside his best interest."