The input pins of the OPAx210 are protected from excessive differential voltage with back-to-back diodes, as shown in Figure 7-1. In most circuit applications, the input protection circuitry has no consequence. However, in low-gain or G = 1 circuits, fast-ramping input signals can forward-bias these diodes because the output of the amplifier cannot respond rapidly enough to the input ramp. This effect is illustrated in Figure 6-35 and Figure 6-36 in Section 6.7. If the input signal is fast enough to create this forward-bias condition, the input signal current must be limited to 10 mA or less. If the input signal current is not inherently limited, an input series resistor can be used to limit the signal input current. This input series resistor degrades the low-noise performance of the OPAx210. See Section 7.3.3 for further information on noise performance.

Figure 7-1 shows an example configuration that implements a current-limiting feedback resistor.

Figure 7-1 Pulsed Operation