To make sure that the composite amplifier remains stable, the phase shift of the BUF634 must remain small throughout the loop gain of the circuit. For a G = +1 op-amp circuit, the BUF634 must contribute little additional phase shift (approximately 20° or less) at the unity-gain frequency of the op amp. Phase shift is affected by various operating conditions that can affect stability of the op amp; see Section 6.8.

Most general-purpose or precision op amps remain unity-gain stable with the BUF634 connected inside the feedback loop as shown. Large capacitive loads can require the BUF634 to be connected for wide bandwidth and stable operation. High-speed or fast-settling op amps generally require the wide bandwidth mode to remain stable and to maintain good dynamic performance. To check for stability with an op amp, look for oscillations or excessive ringing on signal pulses with the intended load, and worst-case conditions that affect phase response of the buffer. Connect the circuit as shown in Figure 8-6. Choose resistors to provide a voltage gain of 23.5 V/V. Select the feedback resistor to be 2.7 kΩ. Choose the input resistor to be 120 Ω.