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TPS565208: Thermal junction calculation

Amir Eshraghi
Expert 1270 points
Part Number: TPS565208

Hi

I was looking at web bench for ic to convert 12V to 5V with 4Amp which I found TPS565208. 

My question is power dissipation and how hot the ic will get

Base my understanding you calculate junction  temp:  (Vout-Vin)Iout x (1-%Efficiency)  x Ramp= (12-5)*4*  (1-.94)*95C/W = 159.6C

But if you look at the web bench you will see the IC junction temperature 80.4C so which one is correct 

even if look at TPS565208 EVM does this board can handle 3Amp without heating up 

 Link to webbench 

  • 0
    TI__Genius 15135 points

    Hi, sir

    we are looking into your question, and will feeback you on next monday.

  • 0 in reply to Zhao Ma
    Expert 1270 points

    Sure I also look at web bench for another part TPS40305DRCR too, my main questions  how do I calculate how hot these devices will be when you have :

    Vin = 12 9Amp

    Vout = 5 4amp

    THank you

  • 0 in reply to Amir Eshraghi
    TI__Expert 4875 points

    Hi Amir,

    Please refer to the webench model indication for the right thermal data. If you would like to calculate the IC junction temp, you will need to use the equation: Ta(25C)+IC Pd*ICThetaJA=IC Tj. For ICThetaJA, it is not reasonable to use 95.9C/W from datasheet for calculation. ICThetaJA is a value that is heavily depending on the PCB board. For the real world PCB, you will always see a much lower ICThetaJA value compared to the datasheet value. So it is good to use 60C/W like the webench showed.

    IC Pd could also refer to the webench data. Or you could just use the power loss as a rough estimation Vout*Iout*(1-eff%)/eff%