OPA445 datasheet(11/25 Pages) TI

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OPA445

SBOS156B − MARCH 1987 − REVISED APRIL 2008

www.ti.com

110

S| − |VO|(V)

100

0.1

A =25_ C

A =85_ C

A = 120_ C

A +[(|VS| − |VO|) IO ×θJA] ≤ TJ (max)

JA =52_ C/W

J (max) = 125_ C

1in x 0.5in, 1oz Cu

Figure 10. SO-8 PowerPAD Safe Operating Area

(with heat-spreader, no airflow)

0.5

1.0

1.5

2.5

3.0

Air−Flow (meters/sec)

2.0

120

100

With Heat−Spreader, 1in x 0.5in, 1oz Cu

No Heat−Spreader

Figure 11. SO-8 PowerPAD Thermal Resistance

(with and without heat-spreader)

0.5

1.0

1.5

2.0

2.5

3.0

Copper Area (inches2)

100

No Airflow

Figure 12. Thermal Resistance vs Circuit Board

Copper Area

POWER DISSIPATION

Power dissipation depends on power supply, signal, and

load conditions. For dc signals, power dissipation is equal

to the product of the output current times the voltage

across the conducting output transistor, PD = IL (VS − VO).

Power dissipation can be minimized by using the lowest

possible power-supply voltage necessary to assure the

required output voltage swing.

For resistive loads, the maximum power dissipation occurs

at a dc output voltage of one-half the power supply voltage.

Dissipation with ac signals is lower. Application Bulletin

SBOA022

explains

how

calculate

measure

dissipation with unusual loads or signals.

The OPA445 can supply output currents of 15mA and

larger. This would present no problem for a standard op

amp operating from

±15V supplies. With high supply

voltages, however, internal power dissipation of the op

amp can be quite large. Operation from a single power

supply (or unbalanced power supplies) can produce even

larger power dissipation since a large voltage is impressed

across the conducting output transistor. Applications with

large power dissipation may require a heat-sink.

HEAT SINKING

Power dissipated in the OPA445 will cause the junction

temperature to rise. For reliable operation junction

temperature should be limited to 125

°C, maximum (150°C

for TO-99 package). Some applications will require a

heat-sink to assure that the maximum operating junction

temperature is not exceeded. In addition, the junction

temperature should be kept as low as possible for

increased

reliability.

Junction

temperature

can

determined according to the following equation:

+ T

) P

Package thermal resistance,

qJA, is affected by mounting

techniques and environments. Poor air circulation and use

of sockets can significantly increase thermal resistance.

Best thermal performance is achieved by soldering the op

amp into a circuit board with wide printed circuit traces to

allow greater conduction through the op amp leads.

Simple clip-on heat sinks (such as a Thermalloy 2257) can

reduce the thermal resistance of the TO-99 metal package

by as much as 50

°C/W. The SO-8 PowerPAD package will

provide lower thermal resistance, especially with a simple

heat-spreader—even

lower

with

heat-sink.

For

additional information on determining heat-sink require-

ments, consult Application Bulletin SBOA021.

(1)

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