BTM1A Agere Systems, BTM1A Datasheet - Page 17

• Manufacturer Part Number: BTM1A
• Description: Dual Differential Transceivers--BTK1A And BTM1A
• Manufacturer: Agere Systems

October 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:
Thermal impedance of the package is referred to as
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
where:
T
T
P
ambient
The power dissipation estimate is derived from two
factors:
Multiplying I
internal power dissipation.
Agere Systems Inc.
j
j
A
D
ja
ja
Ambient use temperature
Device power dissipation
Component placement on the board
Thermal properties of the board
Thermal impedance of the package
Internal device power
Power associated with output terminations
= T
is device junction temperature (°C).
is ambient temperature (°C).
is power dissipation (W).
and is measured in °C rise in junction temperature
is package thermal impedance (junction to
A
—
P
°C/W).
D
CC
ja
times V
CC
provides an estimate of
The power dissipated in the output is a function of the:
Package thermal impedance depends on:
The junction temperature can be calculated using the
previous equation, after power dissipation levels and
package thermal impedances are known.
Figure 16 illustrates the thermal impedance estimates
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:
Termination scheme on the outputs
Termination resistors
Duty cycle of the output
Airflow
Package type (e.g., DIP, SOIC, SOIC/NB)
System ambient temperature
Power dissipation
Package type
Airflow
140
130
120
110
100
90
80
70
60
50
40
0
Figure 16. Power Dissipation
200
DIP
J-LEAD SOIC/GULL WING
400
AIRFLOW (ft./min.)
600
SOIC/NB
BTK1A and BTM1A
800
1000
1200
12-2753F
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