BTF1A Datasheet, PDF (15/16 Pages) Agere Systems – Dual Differential Transceiver BTF1A With Idle Bus Indicator

Data Sheet
March 2001
Dual Differential Transceiver BTF1A
With Idle Bus Indicator
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.
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.
Several factors contribute to the resulting junction tem-
perature of an integrated circuit:
s Ambient use temperature
s Device power dissipation
s Component placement on the board
s Thermal properties of the board
s Thermal impedance of the package
Thermal impedance of the package is referred to as
Θja 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:
Tj = TA + PD Θja
where:
Tj is device junction temperature (°C).
TA is ambient temperature (°C).
PD is power dissipation (W).
Θja is package thermal impedance (junction to
ambient—°C/W).
The power dissipation estimate is derived from two fac-
tors:
s Internal device power
s Power associated with output terminations
Multiplying ICC times VCC provides an estimate of
internal power dissipation.
The power dissipated in the output is a function of the:
s Termination scheme on the outputs
s Termination resistors
s Duty cycle of the output
Package thermal impedance depends on:
s Airflow
s 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.
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:
s System ambient temperature
s Power dissipation
s Package type
s Airflow
140
130
120
110
100
90
80
70
60
50
40
0
SOIC/NB
J-LEAD SOIC/GULL WING
DIP
200 400 600 800 1000 1200
AIRFLOW (ft/min)
12-2753(F)
Figure 16. Power Dissipation
Agere Systems Inc.
15