The internal power dissipation of any amplifier causes the internal (junction) temperature to rise. This phenomenon is called self heating. The absolute maximum junction temperature of the OPAx992-Q1 is 150°C. Exceeding this temperature causes damage to the device. The OPAx992-Q1 has a thermal protection feature that reduces damage from self heating. The protection works by monitoring the temperature of the device and turning off the op amp output drive for temperatures above 170°C. Figure 7-4 shows an application example for the OPA2992-Q1 that has significant self heating because of the power dissipation (0.954 W). In this example, both channels have a quiescent power dissipation while one of the channels has a significant load. Thermal calculations indicate that for an ambient temperature of 55°C, the device junction temperature reaches 180°C. The actual device, however, turns off the output drive to recover towards a safe junction temperature. Figure 7-4 shows how the circuit behaves during thermal protection. During normal operation, the device acts as a buffer so the output is 3 V. When self heating causes the device junction temperature to increase above the internal limit, the thermal protection forces the output to a high-impedance state and the output is pulled to ground through resistor R_L. If the condition that caused excessive power dissipation is not removed, then the amplifier oscillates between a shutdown and enabled state until the output fault is corrected. Please note that thermal performance can vary greatly depending on the package selected and the PCB layout design. This example uses the thermal performance of the SOIC (8) package.

Figure 7-4 Thermal Protection