8.3.4 Driving Capacitive Loads

The OPA2834 drives up to a nominal capacitive load of 10 pF on the output with no special consideration and without the need of R_O. When driving capacitive loads greater than 10 pF, TI recommends using a small resistor (R_O) in series with the output as close to the device as possible. Without R_O, output capacitance interacts with the output impedance (Z_O) of the amplifier causing phase shift in the feedback loop of the amplifier reducing the phase margin. This reduction in the phase margin causes peaking in the frequency response and overshoot and ringing in the pulse response. Interaction with other parasitic elements can lead to further instability or ringing. Inserting R_O isolates the phase shift from the loop gain path and restores the phase margin; however R_O can limit the bandwidth slightly. Figure 49 shows a diagram of driving capacitive loads.

Figure 39 shows the test circuit and shows the recommended values of R_O versus capacitive loads, C_L. See Figure 40 for the frequency responses with various optimized values of R_O with C_L.

Figure 49. Driving Capacitive Loads With the OPA2834