period ranging from a fraction of a second to several minutes or more, depending on package type, signal, load

and thermal environment.

The thermal protection circuit is designed to prevent damage during abnormal conditions. Any tendency to

activate the thermal protection circuit during normal operation is a sign of an inadequate heat sink or excessive

power dissipation for the package type.

The TO-220 package provides the best thermal performance. When the TO-220 is used with a properly sized

heat sink, output is not limited by thermal performance. The TO-263 also has excellent thermal characteristics;

for good heat dissipation, solder the mounting tab to a circuit board copper area. Figure 8-8 shows typical

thermal resistance from junction to ambient as a function of the copper area. The mounting tab of the TO-220

and TO-263 packages is electrically-connected to the V– power supply.

The DIP and SO-8 surface-mount packages are excellent for applications requiring high output current with low

average power dissipation. To achieve the best possible thermal performance with the DIP or SO-8 packages,

solder the device directly to a circuit board. Because much of the heat is dissipated by conduction through

the package pins, sockets degrade thermal performance. Use wide circuit board traces on all the device pins,

including pins that are not connected. With the DIP package, use traces on both sides of the printed circuit board

if possible.

Circuit Board Copper Area

BUF634F

Surface Mount Package

THERMAL RESISTANCE vs

CIRCUIT BOARD COPPER AREA

60

50

40

30

20

10

0

1

2

3

4

5

Copper Area (inches )

2

BUF634F

Surface Mount Package

1oz copper

Figure 8-8. Thermal Resistance vs Circuit Board Copper Area

8.4.1.1 Power Dissipation

Power dissipation depends on power supply voltage, signal, and load conditions. With dc signals, power

dissipation is equal to the product of output current times the voltage across the conducting output transistor,

VS – VO. Power dissipation can be minimized by using the lowest possible power supply voltage necessary to

provide 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. The Power Amplifier Stress And Power Handling Limitations

application bulletin explains how to calculate or measure power dissipation with unusual signals and loads.

Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate

heat sink. For reliable operation, limit the junction temperature to 150°C, maximum. To estimate the margin of

safety in a complete design, increase the ambient temperature until the thermal protection is triggered. The

thermal protection triggers more than 45°C greater than the maximum expected ambient condition of your

application.

BUF634

SBOS030C – AUGUST 2000 – REVISED MARCH 2024

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