NCV8184

http://onsemi.com

11

The Cauer networks generally have physical significance

and may be divided between nodes to separate thermal

behavior due to one portion of the network from another.

The Foster networks, though when sorted by time constant

(as above) bear a rough correlation with the Cauer networks,

are really only convenient mathematical models. Cauer

networks can be easily implemented using circuit simulating

tools, whereas Foster networks may be more easily

implemented using mathematical tools (for instance, in a

spreadsheet program), according to the following formula:

R(t)

+

n

S

i

+ 1

Ri 1−e

−t taui

50

60

70

80

90

0

100

200

300

400

500

600

700

2.0 oz. Cu

Figure 28. DPAK 5−Lead,

qJA as a Function of the Pad Copper Area Including Traces,

Board Material 0.62” Thick FR4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

100

110

120

130

140

150

160

1.0 oz. Cu

1

10

100

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

10

100

1000

Pulse Width (s)

50% Duty Cycle

20%

Non−Normalized Response

10%

5%

2%

Figure 29. SO−8 Thermal Duty Cycle Curves on 1.0 in. Spreader Test Board

1%