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,
V_S − V_O. Power dissipation is 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 less. 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 maximum junction temperature to the value listed in Section 6.3. To estimate the margin of safety in a complete design, increase the ambient temperature until the thermal protection is triggered at 160°C. The thermal protection must trigger more than 35°C greater than the maximum expected ambient condition of the application.