Question

2. A package with a heat sink and fan has a thermal resistance to the ambient of 8 °C/W. The thermal resistance from the die to the package is 2 °C/W. If the package is in a chassis that will never exceed 50 °C and the maximum acceptable die temperature is 110 °C, how much power can the chip dissipate?

Answer 1

To solve this problem it is necessary to apply the concepts related to the Power depending on the temperature and the heat transferred.

By definition the power can be expressed as

$P = \frac{\Delta T}{\Delta Q}$

Where,

$\Delta T = T_m - T_a =$ Change at the temperature, i.e, the maximum acceptable die temperature ($T_m$) with the allowable temperature in chassis ($T_A$)

$\Delta Q = Q_A-Q_D =$ Change in the thermal resistance to ambient ($Q_A$) and the Thermal resistance from die to package ($Q_D$)

Our values are given as,

$T_m=110\°C$

$T_a= 50\°C$

$Q_A= 8\°C/W$

$Q_D= 2\°C/W$

Replacing we have,

$P = \frac{110-50}{8-2}$

$P = 10W$

The power that can dissipate the chip is 10W