OPA2227-EP_13 Datasheet, PDF (9/23 Pages) Texas Instruments – HIGH PRECISION, LOW NOISE OPERATIONAL AMPLIFIER

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.
R_F
500Ω
–
+
Input
OPA2227
Output
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:
R_X = V_S/20 mA - R_SOURCE
(1)
Copyright © 2012, Texas Instruments Incorporated
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