The OPA564-Q1 has thermal sensing circuitry that helps protect the amplifier from exceeding temperature limits. Power dissipated in the OPA564-Q1 causes the junction temperature to rise. Internal thermal shutdown circuitry disables the output when the die temperature reaches the thermal shutdown temperature limit. The OPA564-Q1 output remains shut down until the die has cooled sufficiently; see the Electrical Characteristics, Thermal Shutdown section. When the OPA564-Q1 is in thermal shutdown, the device asserts the T_FLAG pin high. The T_FLAG pin returns low when the device returns to normal operation. Read the T_FLAG pin with a high-impedance digital I/O pin, or buffer the T_FLAG pin.

Depending on load and signal conditions, the thermal protection circuit can cycle on and off. This cycling limits the amplifier dissipation, but can have undesirable effects on the load. Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate heat sink. For reliable, long-term, continuous operation, with I_OUT at the maximum output of 1.5A, limit the junction temperature to 85°C maximum. Figure 7-8 shows the maximum output current versus junction temperature for dc and RMS signal outputs. To estimate the margin of safety in a complete design (including heat sink), increase the ambient temperature until the thermal protection triggers. Use worst-case loading and signal conditions. For good, long-term reliability, thermal protection triggers when the maximum expected ambient condition of the application is exceeded by 35°C.

Figure 7-8 Maximum Output Current vs Junction Temperature

The internal protection circuitry of the OPA564-Q1 is designed to protect against overload conditions; this circuitry was not intended to replace a proper heat sink. Continuously running the OPA564-Q1 into thermal shutdown degrades reliability.