OPA544FSLASH500 datasheet(7/16 Pages) TI2

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OPA544

POWER DISSIPATION

Power dissipation depends on power supply, signal and load

conditions. For dc signals, power dissipation is equal to the

product of output current times the voltage across the con-

ducting output transistor. Power dissipation can be mini-

mized 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

AB-039 explains how to calculate or measure power dissi-

pation with unusual signals and loads.

HEATSINKING

Most applications require a heat sink to assure that the

maximum junction temperature is not exceeded. The heat

sink required depends on the power dissipated and on

ambient conditions. Consult Application Bulletin AB-038

for information on determining heat sink requirements.

The mounting tab of the surface-mount package version

should be soldered to a circuit board copper area for good

heat dissipation. Figure 3 shows typical thermal resistance

from junction to ambient as a function of the copper area.

THERMAL PROTECTION

The OPA544 has thermal shutdown that protects the ampli-

fier from damage. Any tendency to activate the thermal

shutdown circuit during normal operation is indication of

excessive power dissipation or an inadequate heat sink.

The thermal protection activates at a junction temperature of

approximately 155˚C. For reliable operation, junction tem-

perature should be limited to 150˚C, maximum. To estimate

the margin of safety in a complete design (including heat

sink), increase the ambient temperature until the thermal

protection is activated. Use worst-case load and signal con-

ditions. For good reliability, the thermal protection should

trigger more than 25˚C above the maximum expected ambi-

ent condition of your application. This produces a junction

temperature of 125˚C at the maximum expected ambient

condition.

Depending on load and signal conditions, the thermal pro-

tection circuit may produce a duty-cycle modulated output

signal. This limits the dissipation in the amplifier, but the

rapidly varying output waveform may be damaging to some

loads. The thermal protection may behave differently de-

pending on whether internal dissipation is produced by

sourcing or sinking output current.

OUTPUT STAGE COMPENSATION

The complex load impedances common in power op amp

applications can cause output stage instability. Figure 3

shows an output series R/C compensation network (1

Ω in

series with 0.01

µF) which generally provides excellent sta-

bility. Some variation in circuit values may be required with

certain loads.

UNBALANCED POWER SUPPLIES

Some applications do not require equal positive and negative

output voltage swing. The power supply voltages of the

OPA544 do not need to be equal. For example, a –6V

negative power supply voltage assures that the inputs of the

OPA544 are operated within their linear common-mode

range, and that the output can swing to 0V. The V+ power

supply could range from 15V to 65V. The total voltage (V–

to V+) can range from 20V to 70V. With a 65V positive

supply voltage, the device may not be protected from dam-

age during short-circuits because of the larger VCE during

this condition.

OUTPUT PROTECTION

Reactive and EMF-generating loads can return load current

to the amplifier, causing the output voltage to exceed the

power supply voltage. This damaging condition can be

avoided with clamp diodes from the output terminal to the

power supplies as shown in Figure 4. Fast-recovery rectifier

diodes with a 4A or greater continuous rating are recom-

mended.

FIGURE 3. Thermal Resistance vs Circuit Board Copper Area.

THERMAL RESISTANCE vs

CIRCUIT BOARD COPPER AREA

012345

Copper Area (inches2)

OPA544F

Surface Mount Package

1oz copper

Circuit Board Copper Area

OPA544

Surface Mount Package

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