The OPA561 has thermal sensing circuitry that helps protect the amplifier from exceeding temperature limits. Power dissipated in the OPA561 causes the junction temperature to rise. Internal thermal shutdown circuitry shuts down the output when the die temperature reaches approximately 160°C, resetting when the die has cooled to approximately 140°C. Depending on load and signal conditions, the thermal protection circuit can cycle on and off. This cycling limits the dissipation of the amplifier, but can have an undesirable effect 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, limit the junction temperature to 125°C, maximum. To estimate the margin of safety in a complete design (including heat sink), increase the ambient temperature until the thermal protection is triggered. Use worst-case loading and signal conditions. For good, long-term reliability, set the thermal protection to trigger at more than 35°C greater than the maximum expected ambient condition of your application. This configuration produces a junction temperature of 125°C at the maximum expected ambient condition. The internal protection circuitry of the OPA561 is designed to protect against overload conditions, and is not intended to replace a proper heat sink. Continuously running the OPA561 into thermal shutdown can degrade reliability. The E/S pin can be monitored to determine if shutdown has occurred. During normal operation the voltage on the E/S pin is typically greater than (V−) + 2 V. During shutdown, the voltage drops to less than (V−) + 0.8 V.