AN4337

8/14

DocID025012 Rev 1

The temperature increase due to avalanche and the final junction temperature is:

Equation 7

Equation 8

In these working conditions, the MOSFET device (as Table 1 and 2) is safe since the final

junction temperature and the maximum avalanche energy are much lower than data

specifications.

At this point we can calculate the repetitive avalanche energy pulses in order to understand

how many pulses are necessary to raise the junction temperature from an initial 25 °C to the

From the following equation:

Equation 9

We have:

Equation 10

Since the ∆t duration of a single pulse is very short, we have:

Equation 11

Hence, for a period T=20 µs, using Equation 5 we obtain:

C

t

E

Zth

T

avalanche

c

j

c

j

°

=

∆

⋅

=

∆

−

−

7

.

8

2

C

T

T

c

j

°

=

+

=

7

.

33

7

.

8

))

(

)

1

(

)

(

(

2

(max)

t

Zth

T

t

Zth

T

t

t

E

T

a

j

a

j

avalanche

a

j

∆

∆

−

+

∆

∆

=

∆

−

−

−

τ

avalanche

avalanche

a

j

a

j

a

j

E

t

E

t

Zth

T

t

T

T

Zth

2

2

)

(

)

1

(

)

(

(max)









∆

⋅

∆

∆

−

−

∆

=

−

−

W

C

t

Zth

t

Zth

c

j

a

j

/

05

.

0

)

(

)

(

°

=

∆

=

∆

−

−