AN2385

Determination of the power dissipation and its derating factor

9/14

3

Determination of the power dissipation and its

derating factor

The Power Dissipation value is the maximum power that the device can dissipate in

continuous operating mode when the device works in "on state" and the thermal impedance

Power MOSFET datasheets, it is reported at ambient temperature (25°C). In order to

maximum junction temperature. It is possible to demonstrate that such value is around two

Dissipation can be written as:

Equation 5

considering that the guaranteed maximum junction temperature is 150°C or 175°C (see

Figure 5.).

Figure 5.

Power dissipation vs T

The Linear Derating Factor of Power Dissipation factor is defined as the angular coefficient

of the line shown in Figure 5. It can be calculated as:

Equation 6

P

D

T25

° C

=

()

R

DSON T

JMAX I

DSL

()

()

I

DSL

2

•

T

JMAX

25

° C

–

R

THJC

---------------------------------

=

=

∂P

D

∂T

----------

P

D

T25

° C

=

()

T

JMAX

25

° C

–

---------------------------------

1

R

THLJC

--------------------

=

=