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 = (\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 = (110-50)/(8-2)`

`P = 10W`

The power that can dissipate the chip is 10W