BDGLA datasheet(13/16 Pages) AGERE

13 / 16 page

Agere Systems Inc.

Data Sheet

January 1999

BDG1A, BDP1A, BDGLA, BPNGA, BPNPA, and

Quad Differential Drivers

Power Dissipation

System designers incorporating Agere 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:

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

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 ambi-

ent—°C/W).

The power dissipation estimate is derived from two fac-

tors:

Internal device power

Power associated with output terminations

Multiplying ICC times VCC provides an estimate of inter-

nal power dissipation.

The power dissipated in the output is a function of the:

Termination scheme on the outputs

Termination resistors

Duty cycle of the output

Package thermal impedance depends on:

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.

Figure 10 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:

System ambient temperature

Power dissipation

Package type

Airflow

12-2753F

Figure 10. Power Dissipation

DIP

SOIC/NB

J-LEAD SOIC/GULL WING

AIRFLOW (ft./min.)

200

400

600

800

1000

1200

100

110

120

130

140

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