VITESSE
SEMICONDUCTOR CORPORATION
Datasheet
2.5 Gb/s 16-Bit Multiplexer/
Demultiplexer Chipset
VSC8061/VSC8062
Thermal Considerations
The VS8061 and VS8062 are available in ceramic LDCC and thermally enhanced plastic quad flatpacks.
These packages have been enhanced to improve thermal dissipation through low thermal resistance paths from
the die to the exposed surface of the heat spreader. The thermal resistance of the two packages is shown in the
following table
Table 7: Thermal Resistance
Symbol
Description
F Pack
QH Pack
Units
Thermal resistance from
junction to case.
θjc
1.3
2.1
°C/W
Thermal resistance from case to
ambient still air including
°C/W
θca
18.5
30.0
conduction through the leads.
Thermal Resistance with Airflow
Shown in the table below is the thermal resistance with airflow. This thermal resistance value reflects all the
thermal paths including through the leads in an environment where the leads are exposed. The temperature dif-
ference between the ambient airflow temperature and the case temperature should be the worst case power of
the device multiplied by the thermal resistance.
Table 8: Thermal Resistance with Airflow
θca for F Pack
(case to ambient)
Airflow
θca for QH Pack
Units
100 lfpm
200 lfpm
300 lfpm
500 lfpm
15.9
14.9
14.2
13.3
24
21
19
15
oC/W
oC/W
oC/W
oC/W
Thermal Resistance with Heat Sink
The determination of appropriate heat sink to use is as shown below, using the VS8061 in QH package as an
example.
Figure 11: VS8061 in QH Package
TA
θSA
θCS
Page 16
VITESSE SEMICONDUCTOR CORPORATION
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741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
6/22/99
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