OPA2227

Output

R

F

500Ω

Input

–

+

OPA2227-EP

www.ti.com

SBOS594A – MARCH 2012 – REVISED NOVEMBER 2012

APPLICATION INFORMATION

Basic Connection

The OPA2227 is a precision operational amplifier with very low noise. It is unity-gain stable with a slew rate of

2.3 V/

μs and 8-MHz bandwidth. Applications with noisy or high impedance power supplies may require

decoupling capacitors close to the device pins. In most cases, 0.1-

μF capacitors are adequate.

Offset Voltage and Drift

The OPA2227 has very low offset voltage and drift. To achieve highest dc precision, circuit layout and

mechanical conditions should be optimized. Connections of dissimilar metals can generate thermal potentials at

the op amp inputs which can degrade the offset voltage and drift. These thermocouple effects can exceed the

inherent drift of the amplifier and ultimately degrade its performance. The thermal potentials can be made to

cancel by assuring that they are equal at both input terminals. In addition:

•

Keep thermal mass of the connections made to the two input terminals similar.

•

Locate heat sources as far as possible from the critical input circuitry.

•

Shield operational amplifier and input circuitry from air currents such as those created by cooling fans.

Operating Voltage

OPA2227 operational amplifier operates from ±2.5-V to ±18-V supplies with excellent performance. Unlike most

operational amplifiers which are specified at only one supply voltage, the OPA2227 is specified for real-world

applications; a single set of specifications applies over the ±5-V to ±15-V supply range. Specifications are

assured for applications between ±5-V and ±15-V power supplies. Some applications do not require equal

positive and negative output voltage swing. Power supply voltages do not need to be equal. The OPA2227 can

operate with as little as 5 V between the supplies and with up to 36 V between the supplies. For example, the

positive supply could be set to 25 V with the negative supply at –5 V or vice-versa. In addition, key parameters

are assured over the specified temperature range, –55°C to 125°C. Parameters which vary significantly with

operating voltage or temperature are shown in the Typical Performance Curves.

Offset Voltage Adjustment

The OPA2227 is laser-trimmed for very low offset and drift so most applications will not require external

adjustment.

Input Protection

Back-to-back diodes (see Figure 2) are used for input protection on the OPA2227. Exceeding the turn-on

threshold of these diodes, as in a pulse condition, can cause current to flow through the input protection diodes

due to the amplifier’s finite slew rate. Without external current-limiting resistors, the input devices can be

destroyed. Sources of high input current can cause subtle damage to the amplifier. Although the unit may still be

functional, important parameters such as input offset voltage, drift, and noise may shift.

Figure 2. Pulsed Operation

When using the OPA2227 as a unity-gain buffer (follower), the input current should be limited to 20 mA. This can

be accomplished by inserting a feedback resistor or a resistor in series with the source. Sufficient resistor size

can be calculated:

RX = VS/20 mA - RSOURCE

(1)

Copyright © 2012, Texas Instruments Incorporated

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Product Folder Links: OPA2227-EP