11.3 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,
V_S − V_O. Power dissipation is 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. AB-039 Power Amplifier Stress and Power Handling Limitations explains how to calculate or measure power dissipation with unusual signals and loads See www.ti.com for more details.

Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate heat sink. For reliable operation, junction temperature must be limited to 150°C (maximum.) 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 above the maximum expected ambient condition of the application.