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TPS7B81-Q1: Thermal resistance of Case top is higher than thermal resistance of junction to ambient

Sri Viswa Sathiamoorthy
Prodigy 225 points
Part Number: TPS7B81-Q1


Tool/software:

Hi,

The part number used is TPS7B8150QDRVRQ1. It is WSON package

As per datasheet, the thermal resistance of Case top(85.8) is higher than thermal resistance of junction to ambient(72.8). Generally, Rthja will be higher than Rthjc. How to understand these values?

Please guide.

Thanks,

Sri Viswa

  • 0
    TI__Genius 14245 points

    Hi Sri Viswa, 

    There are several variables which can significantly alter the RθJC(top) value, such as the thermal properties of the encapsulation/mold compound and even how close the die is to the top of the package (die can be thicker/thinner and the height at which the die is placed within a specific leadframe can result in the die being closer or farther away from the top of the package). 

    As a general comment, RθJC(top) can be a difficult Thermal Metric to apply to most designs since few people use topside heatsinks and RθJC(top) assumes all of the heat is transferred through the top of the package. In real applications heat is generally transmitted through the bottom of the package/pins to the PCB which acts as the primary heat sink. So if you are trying to estimate the junction temperature based on measuring the temperature at the top of the package it is better to use the ψJT thermal metric which accounts for the heat transmitting through all possible routes. 

    I hope that helps.