VSC8121QI VITESSE [Vitesse Semiconductor Corporation], VSC8121QI Datasheet - Page 12

• Manufacturer Part Number: VSC8121QI
• Description: 2.488GHz SONET/SDH Clock Generator
• Manufacturer: VITESSE [Vitesse Semiconductor Corporation]

Page 12
2.488GHz SONET/SDH
Clock Generator
Thermal Considerations
die to the exposed surface of the heat spreader. The thermal resistance is shown in the Table 7.
Table 7: Thermal Resistance
Thermal Resistance With Airflow
paths including through the leads in an environment where the leads are exposed. The temperature difference
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
Maximum Ambient Temperature Without Heatsink
Table 9: Maximum Ambient Air Temperature Without Heatsink
heat sources and the direction of air flow.
Symbol
JC
CA
This package has been enhanced with a copper heat slug to provide a low thermal resistance path from the
Shown in Table 8 is the thermal resistance with airflow. This thermal resistance value reflects all the thermal
The worst case ambient temperature without use of a heatsink is given by the equation:
where:
T
T
P
Note that ambient air temperature varies throughout the system based on the positioning and magnitude of
CA
A(MAX)
(MAX)
C(MAX)
100 lfpm
200 lfpm
400 lfpm
600 lfpm
100 lfpm
200 lfpm
400 lfpm
600 lfpm
Airflow
Airflow
None
= Theta case to ambient at appropriate airflow
= Ambient Air temperature
= Case temperature (85
= Power (0.7W for VSC8121)
Thermal resistance from junction-to-case.
Thermal resistance from case-to-ambient with no airflow, including conduction through
the leads.
© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: [phone] • Email: [e-mail]
CA
VITESSE
SEMICONDUCTOR CORPORATION
(
28
25
21
18
T
o
C/W)
A(MAX)
T
o
60
65
68
70
72
C for VSC8121)
A(MAX)
o
C
Internet: www.vitesse.com
= T
Description
C(MAX)
- P
(MAX) CA
VSC8121
Data Sheet
o
35.0
C/W
2.0
G52163-0, Rev 4.2
04/16/01