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Original question:

UC1875-SP: ThetaJC the junction to case BOTTOM value

UC1875-SP: 5962-9455502VKA

ned vrtag
Prodigy 10 points
Part Number: UC1875-SP

The CFP Package, 5962-9455502VKA print calls out a "BASE AND SEATING PLANE" Can you clarify what this means? Is this component intended to have a thermal/ground pad or be top cooled? If so, does the previous response that table 7.4 is actually listing junction-board thermal resistance values and NOT resistance of junction-case take into account any thermal/ground or top cooled intent? 

  • 0
    Prodigy 10 points

    I'll add to this can you confirm 5.4C/W is the junction-board resistance and is 27.6C/W the junction-case same as reply on 5962-9455501VRA? Lastly, does TI recommend a thermal interface material under this component or are resistance values given without thermal interface material? Thanks

  • 0
    TI__Genius 9430 points

    Hi,

    The base is the edge of the package that will face the board when the device is attached. The seating plane is the level that the device will sit at once it is attached to the board. For some packages, such as the CFP package for this device, the base and seating plane are the same. For other packages, such as the CDIP package for this device, the base may be elevated slightly above the seating plane.

    I will need some more time to look into your questions about the assumptions made about cooling methods, but in the meantime I highly recommend this document for more information about how TI defines and measures package thermal metrics: https://www.ti.com/lit/an/spra953c/spra953c.pdf

    I will submit a thermal modelling request to confirm the thermal parameters for the CFP package of this device and then update you here. Typically this takes about 2 weeks to complete.

    Thanks,

    Sarah

  • 0
    TI__Genius 9430 points

    Hi, 

    Thanks for your patience. Here are the results of the thermal model for the CFP package of this device:

    Parameter Value Unit
    RθJC(top) Junction-to-case (top) thermal resistance 27.4 °C/W
    RθJC(bot) Junction-to-case (bottom) thermal resistance 2.1 °C/W
    RθJB Junction-to-board thermal resistance 69.6 °C/W
    RθJA Junction-to-ambient thermal resistance 79.7 °C/W
    ψθJT Junction-to-top characterization parameter 20.9 °C/W
    ψθJB Junction-to-board characterization parameter 62.3 °C/W

    This model assumes the package body is not attached to the PCB.

    For this device, there are no specific recommendations for which approach to take for thermal management. Both of the options you mention (top cooling or placing a thermal material between the board and component) would be acceptable.

    Thanks,

    Sarah