8

®

OPA342, 2342, 4342

APPLICATIONS INFORMATION

OPA342 series op amps are unity gain stable and can operate

on a single supply, making them highly versatile and easy to

use.

Rail-to-rail input and output swing significantly increases

dynamic range, especially in low supply applications. Figure

1 shows the input and output waveforms for the OPA342 in

a 10k

Ω load connected to V

sinusoid. Output voltage is approximately 4.997Vp-p.

Power supply pins should be by passed with 0.01pF ceramic

capacitors.

OPERATING VOLTAGE

OPA342 series op amps are fully specified and guaranteed

from +2.7V to +5.5V. In addition, many specifications apply

from –40ºC to +85ºC. Parameters that vary significantly

with operating voltages or temperature are shown in the

Typical Performance Curves.

RAIL-TO-RAIL INPUT

The input common-mode voltage range of the OPA342

series extends 300mV beyond the supply rails. This is

achieved with a complementary input stage—an N-channel

input differential pair in parallel with a P-channel differen-

tial pair (see Figure 2). The N-channel pair is active for input

voltages close to the positive rail, typically (V+) – 1.3V to

300mV above the positive supply, while the P-channel pair

is on for inputs from 300mV below the negative supply to

approximately (V+) –1.3V. There is a small transition re-

gion, typically (V+) – 1.5V to (V+) – 1.1V, in which both

pairs are on. This 400mV transition region can vary 300mV

with process variation. Thus, the transition region (both

stages on) can range from (V+) – 1.8V to (V+) – 1.4V on the

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

Within the 400mV transition region PSRR, CMRR, offset

voltage, offset drift, and THD may be degraded compared to

operation outside this region. For more information on

designing with rail-to-rail input op amps, see Figure 3

“Design Optimization with Rail-to-Rail Input Op Amps.”

FIGURE 2. Simplified Schematic.

V

BIAS1

V

BIAS2

V

V

Class AB

Control

Circuitry

V

O

V–

(Ground)

V+

Reference

Current

FIGURE 1. Rail-to-Rail Input and Output.

5

µs/div

Output (inverted on scope)

Input

5V

0V