To verify op amp stability, an isolation resistor, or Riso is sometimes needed especially when the op amp is

driving capacitive loads. Figure 6-1 is an example of what the isolation resistor architecture looks like.

A

4/A5

–

+

Riso

C

LOAD

GND

Figure 6-1. Example of Isolation Resistor

As shown in Figure 5-17, for capacitive loads above 50pF, it is recommended to include an Riso in the circuit to

maintain at least 45° of phase margin.

Another cause of op amp instability can come from having large impedance feedback resistors. This instability

results in the feedback resistor interacting with the internal input capacitors of the auxiliary amplifiers. There are

two options to correcting this instability. The first one is lowering the resistor values in the feedback loop.

The second option, as shown in Figure 6-2, is to put a feedback capacitor in the feedback loop in parallel with

the feedback resistor.

A

4/A5

–

+

R

f

C

f

R

in

Figure 6-2. Example of Feedback Capacitor

6.4 Device Functional Modes

The device has one mode of operation that applies when operated within the Recommended Operating

Conditions.

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SBOS301B – MAY 2004 – REVISED MARCH 2025

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