10.1.1 Safe Operating Area

Stress on the output transistors is determined both by the output current and by the output voltage across the conducting output transistor, V_S – V_O. The power dissipated by the output transistor is equal to the product of the output current and the voltage across the conducting transistor, V_S – V_O. The Safe Operating Area (SOA curve, Figure 40) shows the permissible range of voltage and current.

Figure 40. 4-Ω Load Plotted on OPA548 SOA for this Application

The safe output current decreases as V_S – V_O increases. Output short circuits are a very demanding case for SOA. A short-circuit to ground forces the full power-supply voltage (V+ or V–) across the conducting transistor. Increasing the case temperature reduces the safe output current that can be tolerated without activating the thermal shutdown circuit of the OPA548. For further insight on SOA, consult Application Bulletin SBOA022.