OPA445 datasheet(21/36 Pages) TI

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POWER DISSIPATION

HEATSINKING

T =T +P q

(1)

0.5

1.0

1.5

2.0

2.5

3.0

CopperArea(inches ),2oz

OPA454

100kW

ComplianceVoltageRange=+47V, 48V

+50V

10kW

100kW

9.9kW

-50V

100W

I =[(V - V )/R ](R /R )

=(V

V )/1k

-IN

+IN

V-

V+

OUT

OPA454

SBOS391 – DECEMBER 2007

Power dissipation depends on power supply, signal,

Power dissipated in the OPA454 causes the junction

and load conditions. For dc signals, power dissipation

temperature to rise. For reliable operation, junction

is equal to the product of the output current times the

temperature should be limited to +125

°C, maximum.

voltage across the conducting output transistor,

Maintaining a lower junction temperature always

PD = IL (VS – VO). Power dissipation can be

results in higher reliability. Some applications require

minimized by using the lowest possible power-supply

a heatsink to assure that the maximum operating

voltage necessary to assure the required output

junction

temperature

not

exceeded.

Junction

voltage swing.

temperature

can

determined

according

Equation 1:

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

Package thermal resistance,

JA,

is affected by

lower because the root-mean square (RMS) value

mounting techniques and environments. Poor air

determines heating. Application Bulletin SBOA022

circulation and use of sockets can significantly

explains how to calculate or measure dissipation with

increase

thermal

resistance

the

ambient

unusual loads or signals. For constant current source

environment. Many op amps placed closely together

circuits, maximum power dissipation occurs at the

also increase the surrounding temperature. Best

minimum output voltage, as Figure 69 shows.

thermal performance is achieved by soldering the op

amp onto a circuit board with wide printed circuit

The OPA454 can supply output currents of 25mA and

traces to allow greater conduction through the op

larger. Supplying this amount of current presents no

amp leads. Increasing circuit board copper area to

problem for some op amps operating from ±15V

approximately 0.5in2 decreases thermal resistance;

supplies. However, with high supply voltages, internal

however, minimal improvement occurs beyond 0.5in2,

power dissipation of the op amp can be quite high.

as shown in Figure 70.

Operation from a single power supply (or unbalanced

power supplies) can produce even greater power

For additional information on determining heatsink

dissipation because a large voltage is impressed

requirements, consult Application Bulletin SBOA021

across the conducting output transistor. Applications

(available for download at www.ti.com).

with high power dissipation may require a heatsink, or

heat spreader.

Figure 70. Thermal Resistance versus Circuit

Board Copper Area

NOTE: R1 = R3 and R2 = R4 + R5.

Figure 69. Precision Voltage-to-Current Converter

with Differential Inputs

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