ZHCSNI6 march 2023 OPA928
ADVANCE INFORMATION
The OPA928 features a patented output stage capable of driving large capacitive loads, and in a unity-gain configuration, directly drives up to 1 nF of pure capacitive load. Increasing the gain enhances the ability of the amplifier to drive greater capacitive loads; see Figure 7-1. The particular op-amp circuit configuration, layout, gain, and output loading are some of the factors to consider when establishing whether an amplifier will be stable in operation.
For additional drive capability in unity-gain configurations, improve capacitive load drive by inserting a small, 10‑Ω to 20‑Ω isolation resistor (RISO) in series with the output; Figure 7-2 shows this resistor. This resistor significantly reduces ringing while maintaining dc performance for purely capacitive loads. However, if there is a resistive load in parallel with the capacitive load, a voltage divider is created, introducing a gain error at the output and slightly reducing the output swing. The error introduced is proportional to the ratio RISO / RL, and is generally negligible at low output levels. RISO modifies the open-loop gain of the system for increased phase margin.