Dual Differential Transceiver BTF1A
With Idle Bus Indicator
Data Sheet
March 2001
The power dissipated in the output is a function of the:
■ Termination scheme on the outputs
■ Termination resistors
Power Dissipation
System designers incorporating Lucent data transmis-
sion drivers in their applications should be aware of
package and thermal information associated with these
components.
■ Duty cycle of the output
Package thermal impedance depends on:
■ Airflow
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 junc-
tion temperature (silicon temperature) of the integrated
circuit.
■ 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.
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 man-
agement issues when using this package type.
Several factors contribute to the resulting junction tem-
perature of an integrated circuit:
■ Ambient use temperature
■ Device power dissipation
In general, system designers should attempt to main-
tain 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:
■ Component placement on the board
■ Thermal properties of the board
■ Thermal impedance of the package
Thermal impedance of the package is referred to as
■ System ambient temperature
■ Power dissipation
■ Package type
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:
■ Airflow
Tj = TA + PD
Θ
ja
140
130
where:
Tj is device junction temperature (°C).
TA is ambient temperature (°C).
PD is power dissipation (W).
120
110
100
90
SOIC/NB
Θ
ja is package thermal impedance (junction to
ambient—°C/W).
80
70
J-LEAD SOIC/GULL WING
The power dissipation estimate is derived from two fac-
tors:
60
50
40
DIP
■ Internal device power
0
200
400
600
800
1000 1200
■ Power associated with output terminations
AIRFLOW (ft/min)
12-2753(F)
Multiplying ICC times VCC provides an estimate of
internal power dissipation.
Figure 16. Power Dissipation
Agere Systems Inc.
15
AGERE [ AGERE SYSTEMS ]
