STRVS parameters

AN4209

8/19

DocID023949 Rev 2

infrared camera and calculate the junction temperature using Equation 6. The lead is the

most interesting reference point to evaluate accurately the average operating junction

1.2.2

Transient parameter

resistance from an input power step function up to reaching a stable value as defined

Equation 7.

Equation 7

Transient thermal impedance can be calculated using Equation 8.

Equation 8

Where:

peak junction temperature to get a better assessment.

Thus from Equation 8, the dynamic change in temperature over the time can be determined

using

Equation 9

The transient thermal impedance diagram provides a quick and simple method to estimate

the rise of junction temperature under transient conditions. Figure 6 below illustrates

transient thermal impedance diagrams of the SMB package. Note that thermal impedances

increase until they reach their asymptotic limit corresponding to their thermal resistance

Junction to reference transient thermal impedance expressed in °C/W.

Pulse duration of the step power expressed in s.

Step power function applied to the die expressed in W.

Junction temperature over the time width, expressed in °C.

Temperature of the reference point expressed in °C.

lim tp

Step

f

p

j

p

TH

P

T

t

T

t

Z

f

j

Re

)

(

)

(

)

Re

(

-

=

-

l

p

l

j

TH

Step

p

j

T

t

Z

P

t

T+

·

=

-

)

(

)

(

)

(