OPA310 datasheet(28/55 Pages) TI

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Input Common-Mode Voltage (V)

-3 -2.5

-2 -1.5

-1 -0.5

0.5

1.5

2.5

-1600

-1200

-800

-400

400

800

1200

1600

D07_

V+ = 2.75 V, V– = –2.75 V

Figure 8-1. OPAx310 Offset Voltage vs Common-

Mode

Common-Mode Voltage (V)

-4

-3

-2

-1

-2000

-1500

-1000

-500

500

1000

1500

2000

D004

V+ = 2.75 V, V– = –2.75 V

Figure 8-2. TLV900x Offset Voltage vs Common-

Mode

8.3.3 Rail-to-Rail Output

Designed as a micro-power, high output current operational amplifier, the OPAx310 delivers a robust output drive

capability. A class AB output stage with common-source transistors is used to achieve full rail-to-rail output swing

capability. At room temperature and for resistive loads up to 2 kΩ, the output swings to within a maximum of

20 mV of either supply rail at 5.5 V power supply. Different load conditions change the ability of the amplifier to

swing close to the rails.

8.3.4 Capacitive Load and Stability

The OPAx310 is designed to be used in applications where driving a capacitive load is required. As with all

operational amplifiers, there can be specific instances where the OPAx310 can become unstable. The particular

operational amplifier circuit configuration, layout, gain, and output loading are some of the factors to consider

when establishing whether or not an amplifier is stable in operation. An operational amplifier in the unity-gain

(1 V/V) buffer configuration that drives a capacitive load exhibits a greater tendency to be unstable than an

amplifier operated at a higher noise gain. The capacitive load, in conjunction with the operational amplifier output

resistance, creates a pole within the feedback loop that degrades the phase margin. The degradation of the

phase margin increases when capacitive loading increases. When operating in the unity-gain configuration, the

OPAx310 remains stable with a pure capacitive load up to approximately 75 pF with a good phase margin of

40° typical and has no sustained oscillations up to 250 pF. The equivalent series resistance (ESR) of some

very large capacitors (CL greater than 1 μF) is sufficient to alter the phase characteristics in the feedback loop

such that the amplifier remains stable. Increasing the amplifier closed-loop gain allows the amplifier to drive

increasingly larger capacitance. This increased capability is evident when measuring the overshoot response of

the amplifier at higher voltage gains.

One technique for increasing the capacitive load drive capability of the amplifier operating in a unity-gain

configuration is to insert a small resistor (typically 10 Ω to 20 Ω) in series with the output, as shown in Figure 8-3.

This resistor significantly reduces the overshoot and ringing associated with large capacitive loads. One possible

problem with this technique, however, is that a voltage divider is created with the added series resistor and any

resistor connected in parallel with the capacitive load. The voltage divider introduces a gain error at the output

that reduces the output swing.

OPA310, OPA2310, OPA4310

SBOSAA1C – APRIL 2022 – REVISED SEPTEMBER 2022

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