Quad Differential Receivers
BRF1A, BRF2A, BRS2B, BRR1A, and BRT1A
Data Sheet
April 2001
Power Dissipation
System designers incorporating Agere data
transmission drivers in their applications should be
aware of package and thermal information associated
with these components.
Proper thermal management is essential to the long-
term reliability of any plastic encapsulated integrated
circuit. Thermal management is especially important
for surface-mount devices, given the increasing circuit
pack density and resulting higher thermal density. A
key aspect of thermal management involves the
junction temperature (silicon temperature) of the
integrated circuit.
Several factors contribute to the resulting junction
temperature of an integrated circuit:
s
s
s
s
s
The power dissipated in the output is a function of the:
s
s
s
Termination scheme on the outputs
Termination resistors
Duty cycle of the output
Package thermal impedance depends on:
s
s
Airflow
Package type (e.g., DIP SOIC, SOIC/NB)
,
The junction temperature can be calculated using the
previous equation, after power dissipation levels and
package thermal impedances are known.
for the various package types as a function of airflow.
This figure shows that package thermal impedance is
higher for the narrow-body SOIC package. Particular
attention should, therefore, be paid to the thermal
management issues when using this package type.
In general, system designers should attempt to
maintain junction temperature below 125 °C. The
following factors should be used to determine if specific
data transmission drivers in particular package types
meet the system reliability objectives:
s
s
s
Ambient use temperature
Device power dissipation
Component placement on the board
Thermal properties of the board
Thermal impedance of the package
Thermal impedance of the package is referred to as
Θ
ja
and is measured in °C rise in junction temperature
per watt of power dissipation. Thermal impedance is
also a function of airflow present in system application.
The following equation can be used to estimate the
junction temperature of any device:
T
j
= T
A
+
P
D
Θ
ja
where:
System ambient temperature
Power dissipation
Package type
Airflow
s
140
130
THERMAL RESISTANCE
Θ
ja
(°C/W)
120
110
100
90
80
70
60
50
40
0
200
DIP
400
600
800
1000
1200
J-LEAD SOIC/GULL WING
SOIC/NB
T
j
is device junction temperature (°C).
T
A
is ambient temperature (°C).
P
D
is power dissipation (W).
Θ
ja
is package thermal impedance (junction to
ambient
—
°C/W).
The power dissipation estimate is derived from two
factors:
s
s
Internal device power
Power associated with output terminations
Multiplying I
CC
times V
CC
provides an estimate of
internal power dissipation.
AIRFLOW (ft./min.)
12-2753(F)
Figure 11. Power Dissipation
8
Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
