OPA2340EASLASH2K5 datasheet(13/46 Pages) TI2

13 / 46 page

5kW

OPAx340

10mA max

V+

OUT

OVERLOAD

OPA340, OPA2340, OPA4340

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SBOS073C – SEPTEMBER 1997 – REVISED AUGUST 2016

Product Folder Links: OPA340 OPA2340 OPA4340

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7.3 Feature Description

7.3.1 Operating Voltage

The OPA340 series operational amplifiers are fully specified from 2.7 V to 5 V. However, supply voltage may

range from 2.5 V to 5.5 V. Parameters are ensured over the specified supply range—a unique feature of the

OPA340 series. In addition, many specifications apply from –40°C to 85°C. Most behavior remains virtually

unchanged throughout the full operating voltage range. Parameters which vary significantly with operating

voltages or temperature are shown in the Typical Characteristics.

7.3.2 Rail-to-Rail Input

The input common-mode voltage range of the OPA340 series extends 500 mV beyond the supply rails. This

extended range is achieved with a complementary input stage—an N-channel input differential pair in parallel

with a P-channel differential pair. The N-channel pair is active for input voltages close to the positive rail, typically

(V+) – 1.3 V to 500 mV above the positive supply, while the P-channel pair is on for inputs from 500 mV below

the negative supply to approximately (V+) – 1.3 V. There is a small transition region, typically (V+) – 1.5 V to

(V+) – 1.1 V, in which both pairs are on. This 400-mV transition region can vary ±300 mV with process variation.

Thus, the transition region (both stages on) can range from (V+) – 1.8 V to (V+) – 1.4 V on the low end, up to

(V+) – 1.2 V to (V+) – 0.8 V on the high end.

OPA340 series operational amplifiers are laser-trimmed to the reduce offset voltage difference between the N-

channel and P-channel input stages, resulting in improved common-mode rejection and a smooth transition

between the N-channel pair and the P-channel pair. However, within the 400-mV transition region PSRR, CMRR,

offset voltage, offset drift, and THD may be degraded compared to operation outside this region.

A double-folded cascode adds the signal from the two input pairs and presents a differential signal to the class

AB output stage. Normally, input bias current is approximately 200 fA; however, input voltages exceeding the

power supplies by more than 500 mV can cause excessive current to flow in or out of the input pins. Momentary

voltages greater than 500 mV beyond the power supply can be tolerated if the current on the input pins is limited

to 10 mA. This current limiting is easily accomplished with an input resistor, as shown in Figure 24. Many input

signals are inherently current-limited to less than 10 mA; therefore, a limiting resistor is not required.

Figure 24. Input Current Protection for Voltages Exceeding the Supply Voltage

7.3.3 Rail-to-Rail Output

A class AB output stage with common-source transistors is used to achieve rail-to-rail output. For light resistive

loads (> 50 k

Ω), the output voltage is typically a few millivolts from the supply rails. With moderate resistive loads

(2 k

Ω to 50 kΩ), the output can swing to within a few tens of millivolts from the supply rails and maintain high

open-loop gain (see Figure 15).

7.3.4 Capacitive Load and Stability

OPA340 series operational amplifiers can drive a wide range of capacitive loads. However, all operational

amplifiers under certain conditions can become unstable. operational amplifier configuration, gain, and load value

are some of the factors to consider when determining stability. An operational amplifier in unity-gain configuration

is most susceptible to the effects of capacitive load. The capacitive load reacts with the output resistance of the

operational amplifier, along with any additional load resistance, to create a pole in the small-signal response that

degrades the phase margin. In unity-gain configuration, the OPA340 series operational amplifiers perform well,

with a pure capacitive load up to approximately 1000 pF. Increasing gain enhances the amplifier ability to drive

more capacitance (see Figure 21).

OPA2340EA/2K5 Datasheet(PDF) 13 Page - Texas Instruments

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