VITESSE
SEMICONDUCTOR CORPORATION
Data Sheet
2.48832Gb/s 16:1 SONET/SDH
Transceiver with Integrated Clock Generator
VSC8140
Package Thermal Considerations
This package has been enhanced with a copper heat slug to provide a low thermal resistance path from the
die to the exposed surface of the heat spreader. The thermal resistance is shown in the following table:
Table 6: Thermal Resistance
Symbol
Description
°C/W - (BGA)
°C/W (PQFP)
θ
Thermal resistance from junction to case.
2.2
1.34
jc
Thermal resistance from case to ambient with no airflow,
including conduction through the leads.
θ
18.5
25.0
ca
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 7: Thermal Resistance with Airflow
Airflow
θca (oC/W) (BGA)
θca (oC/W) (PQFP)
100 lfpm
200 lfpm
400 lfpm
18
17
16
21
18
16
Maximum Ambient Temperature without Heatsink
The worst case ambient temperature without use of a heatsink is given by the equation:
TA(MAX) = TC(MAX) – P(MAX)θCA
where:
θ
Theta case to ambient at appropriate airflow
Ambient Air temperature
CA
A(MAX)
Τ
Τ
P
o
Case temperature (110 C for VSC8140)
Power (2.75 W for VSC8140)
)
C(MAX
(MAX)
Page 32
VITESSE SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
G52251-0, Rev. 4.0
9/6/00
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
