The OPAx863 include overload power limiting that limits the increase in device quiescent current with output saturated to either of the supplies. Typically, when an amplifier output saturates, the two inputs are pulled apart, which can enable the slew-boost circuit. The input differential voltage is an error voltage in negative feedback that the amplifier core nullifies by engaging the slew-boost circuit and driving the output stage deeper into saturation. After the input to an amplifier attains a value large enough to saturate the output, any further increase in this input excitation results in a finite input differential voltage. As the output stage transistor is pushed deeper into saturation, the base-to-collector current gain (h_FE) drops with an increase in the base and collector current, and an increase in the device quiescent current. This increase in quiescent current can cause a catastrophic failure in multichannel, high-gain, high-density front-end designs, and reduce operating lifetime in portable, battery-powered systems.

The OPAx863 overload power limiting includes an intelligent output saturation-detection circuit that limits the device quiescent current to 2.2-mA per channel under dc overload conditions. This increase in quiescent current is smaller with ac input or output and output saturation duration for only a fraction of the overall signal time period. Table 8-1 compares the increase in quiescent current with 50‑mV input overdrive for OPAx863 devices and other voltage-feedback amplifiers without overload power limit.