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How do I calcuate the case temperature of an IC?

Latest Updated:03/23/2009

Question:

How do I calcuate the case temperature of an IC?

Answer:

"The case temperature could be calculated with following formulas:

 

1:  Tj = Ta + Theta-ja x Q

2:  Tj = Tc + Theta-jc x Q

==>

3:  Tc = Ta + Theta-ja x Q - Theta-jc x Q

Ta       = ambient temperature

Tc       = case tempaerature

Tj       = junction temperature

Theta-ja  = thermal resistance junction-ambient

Theta-jc  = thermal resistance junction-case

Q        = power dissipation

e.g.

device: SH7709, SH7729

package: LQFP208-28x28-0.5 (Renesas code FP-208C)

Power dissipation: Q = 0,8 W

  Tc max = Ta max + (Theta-ja - Theta-jc) x Q

         = 85C  + (47C/W  - 7 C/W) x 0,8 W

         = 117 C"

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