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LT8646SEV How to know junction temperature?


We are using LT8646SEV and doing a simulation with LT powercad for 24V in 12V out and 8A current the tool tells me that that tj= 179 C,

If I do the formula in the datasheet the value is very similar, is not 172C very high for TJ? I can not find in the datasheet what is the maximum TJ?

Any suggestions to find TJ max? I am using TJ = TA + (PD • θJA) and its very similar to the LTCAD value

  • Dear Manuel,

    if you just skip from page one of the ds to page 2 you will find the abs max ratings. Depending on the purchased temp grade the max junction temperature might be 125C or 150C. Hence an application where LTpowerCAD calculates 175C will not to work for long.

    best regards


  • Hello

    Thank you for your answer.

    I quite confuse because even if I run half current 4A the TJ is around 132. I use this formula TJ = TA + (PD • θJA)

    where TA=30, PD in cad = 4 θJA = 21 or 31 if Apply this the TJ ~132C this is higher than datasheet 125C.

    I can not understand a company making regulator that you can not run half of its current because the TJ will be so high 

    I read that most of the heat you ist dissipated through the PCB so maybe this formula it's not accurate

    Am I missing something here?

    I also get from this document that you can use  but I am not sure 

    I am using the same specs and components as the DC2660A - Demo Board.


  • You may want to check other possible solution with switches external so you can get higher output current. Please see link below. I looked at LTC7800 for your application.

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