7.3 Feature Description

7.3.1 Input Voltage and Zero-Crossover Functionality

The OPAx388-Q1 input common-mode voltage range extends 0.1 V beyond the supply rails. This amplifier

family is designed to cover the full range without the troublesome transition region found in some other rail-to-rail

amplifiers. Operating a complementary rail-to-rail input amplifier with signals traversing the transition region

results in unwanted non-linear behavior and polluted spectral content. Figure 7-1 and Figure 7-2 contrast

the performance of a traditional complementary rail-to-rail input stage amplifier with the performance of the

zero-crossover OPAx388-Q1. Significant harmonic content and distortion is generated during the differential pair

transition (such a transition does not exist in the OPAx388-Q1). Crossover distortion is eliminated through the

use of a single differential pair coupled with an internal low-noise charge pump. The OPAx388-Q1 maintain

noise, bandwidth, and offset performance throughout the input common-mode range, thus reducing printed

circuit board (PCB) and bill of materials (BOM) complexity through the reduction of power-supply rails.

±20

±15

±10

±5

0

5

10

15

20

±3

±2

±1

0

1

2

3

Input Common-mode Voltage (V)

Complementary Input Stage

OPA388 Zero-Crossover Input Stage

C003

V

V

Figure 7-1. Input Crossover Distortion

Nonlinearity

±140

±120

±100

±80

±60

±40

±20

0

10

100

1k

10k

Frequency (Hz)

C004

Traditional Rail-to-Rail

Input Stage

OPA388 Zero-Crossover Input Stage

Figure 7-2. Input Crossover Distortion

Spectral Content

Typically, input bias current is approximately ±30 pA. Input voltages exceeding the power supplies, however,

can cause excessive current to flow into or out of the input pins. Momentary voltages greater than the power

supply can be tolerated if the input current is limited to 10 mA. This limitation is easily accomplished with an input

resistor, as shown in Figure 7-3.

10 mA max

5 NŸ

+5V

Current-limiting resistor

required if input voltage

exceeds supply rails by

> 0.3V.

Copyright © 2016, Texas Instruments Incorporated

Figure 7-3. Input Current Protection

www.ti.com

OPA388-Q1, OPA2388-Q1

SBOS989A – AUGUST 2020 – REVISED NOVEMBER 2021

Copyright © 2021 Texas Instruments Incorporated

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Product Folder Links: OPA388-Q1 OPA2388-Q1