11

FN6378.2

September 13, 2007

Applications Information

Introduction

The ISL28168 is a single CMOS rail-to-rail input, output

(RRIO) operational amplifier with an enable feature. The

ISL28268 is a dual version without the enable feature. Both

devices are designed to operate from single supply (2.4V to

5.5V) or dual supplies (±1.2V to ±2.75V).

Rail-to-Rail Input/Output

Many rail-to-rail input stages use two differential input pairs,

a long-tail PNP (or PFET) and an NPN (or NFET). Severe

penalties have to be paid for this circuit topology. As the

input signal moves from one supply rail to another, the

operational amplifier switches from one input pair to the

other causing drastic changes in input offset voltage and an

undesired change in magnitude and polarity of input offset

current.

The ISL28168 and ISL28268 achieve input rail-to-rail

operation without sacrificing important precision

specifications and degrading distortion performance. The

devices’ input offset voltage exhibits a smooth behavior

throughout the entire common-mode input range. The input

bias current versus the common-mode voltage range gives

us an undistorted behavior from typically 100mV below the

negative rail and 0.25V higher than the V+ rail. The CMOS

output stage features excellent drive capability, typically

swinging to within 6mV of either rail with a 100k

Ω load.

Pin Descriptions

ISL28168

(6 Ld SOT-23)

ISL28268

(8 Ld SOIC)

(8 Ld MSOP)

PIN NAME

FUNCTION

EQUIVALENT CIRCUIT

NC

Not connected

4

2 (A)

6 (B)

IN-

IN- (A)

IN- (B)

inverting input

Circuit 1

3

3 (A)

5 (B)

IN+

IN+ (A)

IN+ (B)

Non-inverting input

See Circuit 1

2

4

V-

Negative supply

Circuit 2

1

1 (A)

7 (B)

OUT

OUT (A)

OUT (B)

Output

Circuit 3

6

8

V+

Positive supply

See Circuit 2

5EN

Chip enable

Circuit 3

IN+

IN-

V+

V-

V+

V-

CAPACITIVELY

COUPLED

ESD CLAMP

V+

V-

OUT

LOGIC

PIN

V+

V-

ISL28168, ISL28268