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

Output

R

F

Input

-

+

R

I

Figure 7-1. Pulsed Operation

7.3.3 Noise Performance

Figure 7-2 shows the total circuit noise for varying source impedances with the op amp in a unity-gain

configuration (no feedback resistor network, and therefore, no additional noise contributions). Two different op

amps are shown with the total circuit noise calculated. The OPAx210 have very low voltage noise, making these

devices a great choice for low source impedances (less than 2 kΩ). As a comparable, precision FET-input op

amp (very low current noise), the OPA827 has somewhat higher voltage noise, but lower current noise. The

device provides excellent noise performance at moderate to high source impedance (10 kΩ and up). For source

impedance lower than 300 Ω, the OPA211 may provide lower noise.

The equation in Figure 7-2 shows the calculation of the total circuit noise, with these parameters:

• T = temperature in kelvins

For more details on calculating noise, see Section 8.1.1.

100k

1M

Source Resistance, R (Ω)

S

100

1k

10k

10k

1k

100

10

1

R

S

E

O

E

= e

+ (i R ) + 4kTR

O

n

n

S

S

2

2

2

Resistor Noise

OPA827

OPAx210

Figure 7-2. Noise Performance of the OPAx210 and OPA827 in Unity-Gain Buffer Configuration

7.3.4 Phase-Reversal Protection

The OPAx210 have internal phase-reversal protection. Many FET- and bipolar-input op amps exhibit a phase

reversal when the input is driven beyond the linear common-mode range. This condition is most often

encountered in noninverting circuits when the input is driven beyond the specified common-mode voltage range,

causing the output to reverse into the opposite rail. The input circuitry of the OPAx210 prevents phase reversal

with excessive common-mode voltage; instead, the output limits into the appropriate rail (see Figure 6-30).

OPA210, OPA2210

SBOS924F – SEPTEMBER 2018 – REVISED JANUARY 2021

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