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UC2843: Tj=Ta / electrical characteristics requirement?

Hans
Genius 12725 points
Part Number: UC2843

Hello Team,

may I kindly ask you to clarify what this Tj=Ta means, please?

On one side the UC2843 is specified for ambient temp range from -40°C to 85°C, correct?

But in my understanding below requirement can only be achieved if power losses are zero...and this is not realistic

Thanks and Best Regards,

Hans

  • 0
    TI__Mastermind 47705 points

    Hi,

    Tj = Ta condition is achieved at production test when using a strong thermal stream to the device. The forced air flow brings Tj = Ta as practically the device cannot accumulate heat meaningfully to differentiate Tj from Ta. The device under test does not have power stage. Power losses do not have to be zero in terms of theory - it is practically at about that level as the air flow is very strong, and power applied to the IC is small. This is the meaning of Tj =  Ta. Ta is the temperature of forced air to the device, the device under test has no power stage, Tj is assumed = Ta. 

  • 0 in reply to Hong Huang
    TI__Mastermind 47705 points

    Also, the time for test is short which is another factor the heat cannot accumulate to make Tj rise up meaningfully from Ta.

  • 0 in reply to Hong Huang
    TI__Genius 12725 points

    Hi and thanks for fast reply! 

    But what does that mean for the parameters? Are they valid for -40°C to 85°C? E.g. Unity GBW is specified at 25°C only with 0.7MHz minimum. I.e. we don't know the bandwidth over the whole temperature range...

    Best Regards, Hans

  • 0 in reply to Hans
    TI__Mastermind 47705 points

    Hi,

    That is different. Tj = Ta means a test made at Ta with strong thermal stream and in short time. If there is no test on a particular temperature, then there is no. 

    Your mentioned unit gain, there is a note, it says the parameter is based on the design and not tested.

    So if a parameter is tested, it is with Tj = Ta as indicated, if it is not tested, then it is not tested. If you need a parameter not tested, you need to ask the associated product line with your business case.

  • 0 in reply to Hong Huang
    TI__Genius 12725 points

    Hello,

    I understand better now. Just to be sure, e.g. Vvref  has been tested at Ta=Tj=25°C with +/-1%, correct?

    Vvfb has not been tested and can vary between 2.45V and 2.55V at -40°C to 85°C?

    Thanks and Best Regards,

    Hans

  • 0 in reply to Hans
    TI__Mastermind 47705 points

    Hi,

    With all conditions listed, so need to include IVREF = 1mA.

    VVFB is tested and between 2.45V and 2.55V in the temperature range of -40C to 85C, and with the test conditions on the Table top.

  • 0 in reply to Hong Huang
    TI__Genius 12725 points

    thank you!