8.3 Feature Description

8.3.1 Operating Voltage

The OPAx620 is specified over a power-supply range of 2.7V to 5.5V (±1.35V to ±2.75V). However, the supply

voltage ranges from 2.5V to 5.5V (±1.25V to ±2.75V).

8.3.2 Rail-to- Rail Input

The specified input common-mode voltage range of OPAx620 extends 100mV 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; see also Section 8.2. The N-channel pair is active for input voltages close to the

positive rail, typically (V+) − 1.2V to 100mV greater than the positive supply. The P-channel pair is active for

inputs from 100mV less than the negative supply to approximately (V+) − 1.2V. There is a small transition region,

typically (V+) − 1.5V to (V+) − 0.9V, in which both pairs are active. This 600mV transition region vary ±500mV

with process variation. Therefore, the transition region (both input stages active) range from (V+) − 2V to (V+) −

1.5V on the low end, up to (V+) − 0.9V to (V+) − 0.4V on the high end.

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

AB output stage.

8.3.3 Rail-to- Rail Output

A class AB output stage with common-source transistors achieves rail-to-rail output. For high-impedance loads

(> 200Ω), the output voltage swing is typically 30mV from the supply rails. With 10Ω loads, a useful output swing

is achieved while maintaining high open-loop gain.

8.3.4 Output Drive

The OPAx620 output stage supplies a ±100mA continuous output current and yet provides approximately 3.5V

of output swing on a 5V supply. For maximum reliability, do not run a continuous dc current in excess of

±100mA.

8.3.5 Capacitive Load and Stability

The OPAx620 can drive a wide range of capacitive loads. However, all op amps may become unstable under

certain conditions. Key factors affecting stability include op amp configuration, gain, and load value. Unity-gain

configuration makes op amps most susceptible to capacitive loading effects. The capacitive load interacts with

the device output resistance and any additional load resistance, creating a pole in the small-signal response

that reduces phase margin. See also the Frequency Response vs Capacitive Load typical characteristic curve

(Frequency Response for Various CL Values).

The OPAx620 topology enhances the ability to drive capacitive loads. In unity gain, these op amps perform well

with large capacitive loads. See also the Figure 6-14 typical characteristic curves.

Figure 8-1 shows one method of improving capacitive load drive in the unity-gain configuration is to insert a 10Ω

to 20Ω resistor in series with the output. This configuration significantly reduces ringing with large capacitive

loads; see the Frequency Response for Various CL Values typical characteristic curve. However, if there is a

resistive load in parallel with the capacitive load, RS creates a voltage divider. This voltage division introduces a

DC error at the output and slightly reduces output swing. This error can be insignificant. For instance, with RL =

10kΩ and RS = 20Ω, there is an error of approximately 0.2% at the output.

V+

OPAx620

V

IN

V

OUT

R

S

R

L

C

L

GND

Figure 8-1. Series Resistor in Unity- Gain Configuration Improves Capacitive Load Drive

OPA620, OPA2620

SLOSEG2A – APRIL 2026 – REVISED JUNE 2026

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