Driving Capacitive Loads With Op Amps

Operational amplifiers (op amps) that drive large capacitive loads tend to have peaking and oscillation problems when they are not properly compensated. Other problems include: reduced bandwidth, lower output slew rate, and higher power consumption. This application note explains why these problems occur, how to modify the op amp circuit for better performance, and how to quickly compute circuit values. In order to understand how capacitive loads affect op amps, we must look at the op amp output impedance and bandwidth. Figure 1 shows a simplified AC model of an op amp configured for a non-inverting gain of GN. The open-loop gain is represented by the dependent source with gain AOL(s), where s = j??= j2?f. The output stage is represented by the resistor RO (open-loop output resistance).