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OPA131/2131/4131

®

APPLICATIONS INFORMATION

OPA131 series op amps are unity-gain stable and suitable

for a wide range of general-purpose applications. Power

supply pins should be bypassed with 10nF ceramic capaci-

tors or larger.

OPA131 series op amps are free from unexpected output

phase-reversal common with FET op amps. Many FET-

input op amps exhibit phase-reversal of the output when the

input common-mode voltage range is exceeded. This can

occur in voltage-follower circuits, causing serious problems

in control loop applications. All circuitry is completely

independent in dual and quad versions, assuring normal

behavior when one amplifier in a package is overdriven or

short-circuited.

OFFSET VOLTAGE TRIM

The OPA131 (single op amp version) provides offset

voltage trim connections on pins 1 and 5. Offset voltage

can be adjusted by connecting a potentiometer as shown in

Figure 1. This adjustment should be used only to null the

offset of the op amp, not system offset or offset produced

by the signal source.

V+

V–

100k

Ω

OPA131

(Single op amp only)

Trim Range: ±20mV typ

OPA131

6

7

5

4

3

2

1

FIGURE 1. OPA131 Offset Voltage Trim Circuit.

INPUT BIAS CURRENT

The input bias current is approximately 5pA at room tem-

perature and increases with temperature as shown in the

typical performance curve “Input Bias Current vs Tempera-

ture.”

Input bias current also varies with common-mode voltage

and power supply voltage. This variation is dependent on the

voltage between the negative power supply and the com-

mon-mode input voltage. The effect is shown in the typical

curve “Input Bias Current vs Common-Mode Voltage.”