OPA347SASLASH3K datasheet(7/21 Pages) TI

7 / 21 page

OPA347, 2347, 4347

SBOS167C

www.ti.com

APPLICATIONS INFORMATION

The OPA347 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 dy-

namic range, especially in low supply applications. Figure 1

shows the input and output waveforms for the OPA347 in

unity-gain configuration. Operation is from VS = +5V with a

100k

Ω load connected to V

S/2. The input is a 5VPP sinusoid.

Output voltage is approximately 4.995VPP.

Power-supply pins should be bypassed with 0.01

µF ceramic

capacitors.

OPERATING VOLTAGE

The OPA347 series op amps are fully specified and en-

sured from 2.5V to 5.5V. In addition, many specifications

apply from –55

°C to +125°C. Parameters that vary signifi-

cantly with operating voltages or temperature are shown in

the Typical Characteristics.

RAIL-TO-RAIL INPUT

The input common-mode voltage range of the OPA347

series extends 200mV beyond the supply rails. This is

achieved with a complementary input stage—an N-channel

input differential pair in parallel with a P-channel differential

pair, as shown in Figure 2. The N-channel pair is active for

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

to 200mV above the positive supply, while the P-channel pair

is on for inputs from 200mV below the negative supply to

approximately (V+) – 1.3V. There is a small transition region,

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+) – 1.65V to (V+) – 1.25V on the low

end, up to (V+) – 1.35V to (V+) – 0.95V on the high end.

Within the 400mV transition region PSRR, CMRR, offset

voltage, and offset drift may be degraded compared to

operation outside this region. For more information on de-

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

Design

Optimization with Rail-to-Rail Input Op Amps.

FIGURE 2. Simplified Schematic.

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

BIAS1

BIAS2

IN+

IN–

Class AB

Control

Circuitry

V–

(Ground)

V+

Reference

Current

Input

Output (inverted on scope)

1V/div

G = +1, V

S = +5V

µs/div

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