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8

Agere Systems Inc.

Data Sheet

April 2001

BRF1A, BRF2A, BRS2B, BRR1A, and BRT1A

Quad Differential Receivers

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

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

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:

where:

The power dissipation estimate is derived from two

factors:

s

Internal device power

s

Power associated with output terminations

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 11 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:

s

System ambient temperature

s

Power dissipation

s

Package type

s

Airflow

12-2753(F)

Figure 11. Power Dissipation

DIP

SOIC/NB

J-LEAD SOIC/GULL WING

AIRFLOW (ft./min.)

200

400

600

800

1000

1200

0

40

50

60

70

80

90

100

110

120

130

140