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LTC3376 Tj

Hi

I'm a DFAE in Japan. I try to recommend LTC3376 to the customer. I'd like to know the difference between Tj and Die temperature. If the power dissipation each channel would be 1W in other words total power dissipation as 4W, could Tj at Ta=60degC be calculated 4W*35degC/W+60degC=200degC>125degC ? The customer's spec is as follows. Is it impossible to implement ?

use CFG(3:0)=0000. Vin=12V. Ta=60degC. Buck1 & 2 for Vo=6V, Io=2.4A. Buck3 for Vo=5.8V, Io=1.7A. Buck4 for Vo=6.5V, Io=1.6A. 

I estimate the total dissipation is 3.43W. Then Tj at Ta=60degC could be calculated about 180degC. Therefore is it impossible for us to recommend LTC3376 to the customer ?

Regards,

Hiroyuki

  

  • Hi Hiroyuki,

    Tj refers to the die junction temperature. You can consider them the same.

    For your specified power dissipation, the calculations are correct. However, your specified power dissipation may be a little pessimistic. It depends on your input voltage, but if you can get up to ~95% efficiency you will see much less heating. Bear in mind also that some of this power loss is in the inductor, so not internal to the IC.

    I can't say for sure, but you may be able to make this work at a reasonable temperature with a good layout. That said, it does seem to be on the edge of plausibility for this part.

    Regards,

    Zack

  • Dear Zack,

    Thank you very much for your support.

    I'm sorry that my calculation include the power loss in the inductor. Then I'll calculate the efficiency again.

    Regards,

    Hiroyuki