During overload or fault conditions, bipolar rail-to-rail output (RRO) amplifiers consume excessive quiescent current (five to seven times) with saturated outputs. With saturated outputs, the output signal is clipped with much higher base current from output predriver stage which results in increase in device quiescent current. During this condition, the negative feedback control is disabled and an input differential voltage appears thereby resulting in an input overdrive. During input overdrive, the slew boost circuit engages causing increase in the tail current and hence the device quiescent current. This overall increase in quiescent current can cause excessive battery discharge in portable products shortening operating lifetime or disturb the thermal equilibrium causing irreversible damage due to increased system power dissipation in a multichannel design.

The OPAx863A includes an intelligent overload detection circuit that monitors for output saturation and limits the base drive from output predriver circuit and disables the slew boost circuit in this condition. Table 7-1 compares the increase in quiescent current with 500-mV input overdrive for OPAx863A devices and other voltage-feedback amplifiers without overload power limit.