NCV7356 ON Semiconductor, NCV7356 Datasheet - Page 18

• Manufacturer Part Number: NCV7356
• Manufacturer: ON Semiconductor

Table 1. SOIC−8 Thermal RC Network Models*
*Bold face items in the Cauer network above, represent the package without the external thermal system. The Bold face items in the Foster network
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.
Both Foster and Cauer networks can be easily implemented
are computed by the square root of time constant R(t) = 24.4 * 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
Junction
Junction
3.13E−05
1.23E−04
3.70E−04
1.28E−03
4.55E−03
1.69E−02
5.86E−02
54 mm
23.944
37.864
71.762
28.053
0.197
0.041
0.093
0.263
1.868
8.332
1.50
C’s
R’s
Cauer
2
Cauer Network
Time constants are not simple RC products.
Amplitudes of mathematical solution are not the resistance values.
Each rung is exactly characterized by its RC−product time constant; Am-
plitudes are the resistances
C
networks
1
R
R
C
1
1
1
Figure 14. Non−Grounded Capacitor Thermal Ladder (“Foster” Ladder)
Figure 13. Grounded Capacitor Thermal Network (“Cauer” Ladder)
714 mm
3.13E−05
1.23E−04
3.70E−04
1.28E−03
4.83E−03
1.75E−02
6.35E−02
24.484
33.670
23.952
21.501
0.333
0.041
0.093
0.263
1.976
8.627
0.212
2.81
C’s
431
R’s
generally
2
C
2
R
R
C
2
2
2
have
Copper Area
W−s/C
W−s/C
W−s/C
W−s/C
W−s/C
W−s/C
W−s/C
W−s/C
W−s/C
W−s/C
Units
C/W
C/W
C/W
C/W
C/W
C/W
C/W
C/W
C/W
C/W
physical
C
http://onsemi.com
3
R
R
C
NCV7356
3
3
3
18
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:
1.00E−06
1.00E−05
1.00E−04
2.44E−02
5.28E−02
1.67E−01
54 mm
0.002
0.038
0.386
16.24
54.81
2.21
12.9
26.2
55.6
71.4
Tau
R’s
1.0
4.7
2
Foster Network
R(t) +
i + 1
714 mm
1.00E−06
1.00E−05
1.00E−04
2.44E−02
5.28E−02
1.67E−01
S
n
0.003
0.041
0.413
2.29
9.32
68.9
94.1
13.4
26.7
36.7
27.6
Tau
R’s
1.1
4.8
4.2
R i 1−e
2
(thermal ground)
−t tau i
(thermal ground)
C
Ambient
n
Ambient
Copper Area
R
R
C
n
n
n
Units
sec
sec
sec
sec
sec
sec
sec
sec
sec
sec
C/W
C/W
C/W
C/W
C/W
C/W
C/W
C/W
C/W
C/W