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11

Table 1. SOIC 16-Lead Thermal RC Network Models

Cu Area

Cauer network

Foster network

C's

C's

Units

Tau

Tau

units

1

1.84E-06

1.84E-06

W-s/C

2.99E-07

2.99E-07

sec

2

8.69E-06

8.69E-06

W-s/C

4.40E-06

4.40E-06

sec

3

2.61E-05

2.61E-05

W-s/C

4.62E-05

4.62E-05

sec

4

8.98E-05

8.98E-05

W-s/C

5.08E-04

5.08E-04

sec

5

2.30E-03

2.30E-03

W-s/C

8.93E-03

8.95E-03

sec

6

2.99E-02

3.07E-02

W-s/C

2.04E-01

2.19E-01

sec

7

1.79E-01

1.90E-01

W-s/C

3.26E+00

2.75E+00

sec

8

7.79E-01

9.94E-01

W-s/C

3.21E+01

2.19E+01

sec

9

5.34E+00

3.98E+00

W-s/C

1.24E+02

1.20E+02

sec

R's

R's

R's

R's

1

0.199

0.199

C/W

0.123

0.123

C/W

2

0.598

0.598

C/W

0.349

0.349

C/W

3

1.795

1.795

C/W

1.057

1.057

C/W

4

4.085

4.085

C/W

4.61

4.61

C/W

5

3.977

3.977

C/W

3.87

3.89

C/W

6

7.509

7.833

C/W

5.77

5.99

C/W

7

19.886

15.247

C/W

13.17

11.38

C/W

8

40.307

24.781

C/W

28.85

15.52

C/W

9

18.193

21.446

C/W

38.75

37.05

C/W

NOTE:

Bold face items in the Cauer network above, represent the package without the external thermal system. The Bold face items in

the Foster network are computed by the square root of time constant R(t) = 225 * sqrt(time(sec)). The constant is derived based

on the active area of the device with silicon and epoxy at the interface of the heat generation.

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