AN2385

Silicon limited drain current

7/14

2

Silicon limited drain current

Usually, in every Power MOSFET datasheet the drain current limit is fixed by the package

limit. It depends on the kind, number and the size of the wires that connect the drain and the

source pads to the respective package pins. However, another important parameter defined

in the Power MOSFET datasheets is the Silicon Limited Drain Current. The Silicon Limited

Drain Current is the maximum drain current that can flow in the device excluding the

package limitation and considering as thermal impedance the junction to case thermal

calculated considering the device in "on state" with a case temperature equal to 25°C and

supposing that it works at the maximum junction temperature. Considering this last

around two times higher at the ambient temperature (25°C). In thermal equilibrium

conditions, the following expression can be written as shown below:

Equation 1

Equation 2

Equation 3

Sometimes, in the Power MOSFET datasheets, the Silicon Limited Drain Current is shown

Equation 4

The Limited Drain Current versus case temperature is also shown in the Figure 4. This is

considering an example where the junction to case thermal resistance equals 0.5°C/W, the

graph, the Package limited Drain Current is also highlighted (75A).

T

JMAX

25

° CR

THJC

P

MAX

•

=

–

P

MAX

R

DSON T

JMAX

()

I

2

DSL

•

=

I

DSL

T

JMAX

25

° C

–

R

DSON T

JMAX

()

R

THJC

•

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

=

I

()

T

JMAX

T

–

R

DSON T

JMAX

()

R

THJC

•

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

=