9

FN6154.5

December 16, 2008

Applications Information

Introduction

The ISL28156 is a single BiMOS rail-to-rail input, output

(RRIO) operational amplifier with an enable feature. The

ISL28256 is a dual version without the enable feature. Both

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

5.0V) or dual supplies (±1.2V to ±2.5V) while drawing only

39µA of supply current per amplifier. This combination of low

power and precision performance makes this device suitable

for a variety of low power applications including battery

powered systems.

Rail-to-Rail Input/Output

These devices feature bi-polar inputs, which have an input

common mode range that extends up to 0.5V beyond the V+

rail, and to within 10mV of the V- rail. The CMOS outputs

typically swing to within about 4mV of the supply rails with a

100k

Ω load. The NMOS sinks current to swing the output in

the negative direction. The PMOS sources current to swing the

output in the positive direction.

Input Protection

All input terminals have internal ESD protection diodes to both

positive and negative supply rails, limiting the input voltage to

within one diode beyond the supply rails. They also contain

back-to-back diodes across the input terminals. For

applications where the input differential voltage is expected to

exceed 0.5V, external series resistors must be used to ensure

the input currents never exceed 5mA (Figure 35).

Enable/Disable Feature

The ISL28156 offers an EN pin that disables the device when

pulled up to at least 2.0V. In the disabled state (output in a

high impedance state), the part consumes typically 10µA. By

disabling the part, multiple ISL28156 parts can be connected

together as a MUX. In this configuration, the outputs are tied

together in parallel and a channel can be selected by the EN

Pin Descriptions

ISL28156

(6 Ld SOT-23)

ISL28156

(8 Ld SOIC)

ISL28256

(8 Ld MSOP)

PIN NAME

FUNCTION

EQUIVALENT CIRCUIT

1, 5

NC

Not connected

42

2 (A)

6 (B)

IN-

IN-_A

IN-_B

Inverting input

Circuit 1

33

3 (A)

5 (B)

IN+

IN+_A

IN+_B

Non-inverting

input

(See Circuit 1)

2

4

4

V-

Negative supply

16

1 (A)

7 (B)

OUT

OUT_A

OUT_B

Output

Circuit 2

6

7

8

V+

Positive supply

5

8

ENABLE

Chip enable

Circuit 3

IN-

V+

V-

IN+

V+

V-

OUT

V+

V-

CE

FIGURE 35. INPUT CURRENT LIMITING

-

+

ISL28156, ISL28256