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TPS548A28: Thermal resistance clarification required

Part Number: TPS548A28

The junction/case (top) thermal resistance for this package is 18.2 deg C/W and junction-to-top characterization parameter is 0.6. which looks very strange as their is a big difference between these two values. can you please confirm if it is correct, and explain the same.

  • Hello Singh 

    ψJT is characterization parameter where the Junction-to-case (top) thermal resistance is pure package related parameter. 

    Yes, it can be confusing. The ψJT is a parameter that characterizes the behavior of the package on a real application environment such as an EVM or customer board only about 2% of the heat will be dissipated on the TOP, about 98% will be dissipated from the bottom to the board and eventually cooling off the device. ΨJT, has been adopted by the industry (JESD51-2). The metric is defined by the Greek character psi (Ψ) rather than theta (θ) because ΨJT is not a true thermal resistance. The characterization parameter ψJT accounts for all heat transfer while measuring the top of the package. System dependent just as in RθJA. 

    Regarding, Junction-to-case (top) thermal resistance , it is pure package related parameter assuming 100% of the heat will be dissipated on the top of the package. it assumes all of the heat is being transferred through the top of the package which is not accurate in real system, the majority of heat will be transferred through to the PCB through the bottom of the package. so that is not that usefully information for real application. This parameter is used to only compare packages.