VITESSE
SEMICONDUCTOR CORPORATION
Data Sheet
2.5Gb/s 16-Bit
Multiplexer/Demultiplexer Chipset
VSC8061/VSC8062
The worst-case temperature rise from case to ambient is given by the equation:
DT = P(MAX)(qSA + qCS
)
where:
q
q
=
=
=
=
=
=
Theta sink-to-ambient
Theta case-to-sink
SA
CS
o
T
T
Air temperature, user supplied (typically +55 C)
A(MAX)
o
Case temperature (+85 C for Industrial range)
C(MAX)
DT
T - T
C A
P
Power (2.0 W for VSC8061)
(MAX)
T
– T
DT
C
A
\ P = ------ = --------------------------
Sq + q
q
SA CS
DT
P
q
= ------ – q
SA
CS
o
o
If T = 55 C and q (user supplied) is typically 0.6 C/W,
A
CS
(85 – 55)°C
= ----------------------------- – 0.6°C ¤ W
q
SA
2W
q
= 14.4°C ¤ W
SA
o
Therefore, to maintain the proper case and junction temperature, a heat sink with a q of 14.4 C/W or less
SA
must be selected at the appropriate air flow.
NOTE: The heat spreader is tied to V in both the VSC8061 and VSC8062.
EE
G52069-0, Rev 4.3
05/11/01
Page 17
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