OPA37 datasheet(9/24 Pages) TI2

9 / 24 page

OPA27, OPA37

SBOS135C

www.ti.com

APPLICATIONS INFORMATION

OFFSET VOLTAGE ADJUSTMENT

The OPA27 and OPA37 offset voltages are laser-trimmed

and require no further trim for most applications. Offset

voltage drift will not be degraded when the input offset is

nulled with a 10k

Ω trim potentiometer. Other potentiometer

values from 1k

Ω to 1MΩ can be used, but V

OS drift will be

degraded by an additional 0.1

µV/°C to 0.2µV/°C. Nulling

large system offsets by use of the offset trim adjust will

degrade drift performance by approximately 3.3

µV/°C per

millivolt of offset. Large system offsets can be nulled without

drift degradation by input summing.

The conventional offset voltage trim circuit is shown in Figure

3. For trimming very small offsets, the higher resolution

circuit shown in Figure 4 is recommended.

The OPA27 and OPA37 can replace 741-type operational

amplifiers by removing or modifying the trim circuit.

THERMOELECTRIC POTENTIALS

The OPA27 and OPA37 are laser-trimmed to microvolt-level

input offset voltages, and for very-low input offset voltage

drift.

Careful layout and circuit design techniques are necessary to

prevent offset and drift errors from external thermoelectric

potentials. Dissimilar metal junctions can generate small

EMFs if care is not taken to eliminate either their sources

(lead-to-PC, wiring, etc.) or their temperature difference (see

Figure 11).

Short, direct mounting of the OPA27 and OPA37 with close

spacing of the input pins is highly recommended. Poor layout

can result in circuit drifts and offsets which are an order of

magnitude greater than the operational amplifier alone.

FIGURE 1. 0.1Hz to 10Hz Noise Test Circuit.

FIGURE 2. Low Frequency Noise.

DUT

OPA111

100k

Ω

4.7

µF

Voltage Gain

Total = 50,000

Ω

NOTE: All capacitor values are for nonpolarized capacitors only.

0.1

µF

Scope

IN = 1MΩ

100k

Ω

24.3k

Ω

4.3k

Ω

110k

Ω

0.1

µF

2.2

µF

0.1Hz TO 10Hz NOISE

1s/div

40nv/div

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