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TPS54326: thermal resistance questions

Mark Chen52
Expert 6675 points
Part Number: TPS54326

Hi Expert,

there is a question for junction to case resistance, to check the datasheet, JC (Top) is 58.1 C/W, which is larger than JA 46.1 C/W, does is make sense? if yes, may i know why JC>JA? 

in general, should be JA>JC. 

I saw another parameter JC(bot), if customer need junction to case resistance, which parameter we suggest to customer? JC (Top) or JC (Bot) ?

Regards,

Mark

  • 0
    TI__Mastermind 24130 points

    Hi Mark,

    This happens occasionally as the tests are separate and unrelated.  Theta-JA assumes a natural convection environment with a 4 layer PCB, so most of the heat is dissipated through the exposed pad and into the board.  Theta-JC (Top) assumes a 1 layer PCB with an infinite heat sink on top of the package designed to force all of the heat to the top of the package.  

    The two different Theta-JC values are related to two different surfaces of the package.  Theta-JC (Bottom) is the thermal resistance from the die to the exposed pad.

    Thanks,
    Amod