Technical Article

MS-2212

www.analog.com

November 2011 | Page 5 of 5

©2011 Analog Devices, Inc. All rights reserved.

Summary

Rail-to-rail output op amps have unique characteristics

when operated as comparators.

The best solutions to improving battery life and increasing

performance are to use a low cost comparator when a

comparator function is required, tying off any used op amp

sections as followers with the noninverting input connected

to a stable voltage within the input voltage range of the op

amp, or using singles and duals as appropriate instead of

quads. Supply current may greatly exceed the “Max” stated

on the data sheet. Under carefully considered conditions,

unused op amps can be used as comparators, but using the

proper mix of op amps and comparators will result in lower

supply current and well-defined performance.

REFERENCES

1. Kester, Walt “Op Amp Inputs, Outputs, Single-Supply,

and Rail-to-Rail Issues” MT-035 Tutorial

www.analog.com/MT-035

2. Frost, Robert “Mountain Interval” New York: Henry

Holt & Company, 1920.

3. ”Comparators” MT-083 Tutorial

www.analog.com/MT-083

4. Sylvan, John, “High-speed comparators provide many

useful circuit functions when used correctly” Analog

Dialogue, Ask the Applications Engineer— 5

www.analog.com/analogdialogue

5. Bryant, James “Using Op Amps as Comparators” 2006

AN-849 at www.analog.com/AN-849

6. Kester, Walt “Using Op Amps As Comparators”

MT-084 Tutorial www.analog.com/MT-084

7. Moghimi, Reza “Amplifiers as Comparators?” Analog

Dialogue Ask the Applications Engineer—31

www.analog.com/analogdialogue

8. Holt, Harry ”OP Amps: To Dual or Not to Dual”

www.eetimes.com

9. ADA4092-4 data sheet www.analog.com/ADA4092-4

10. AD8657 data sheet www.analog.com/AD8657

RESOURCES

For resources and information on op amps,

visit www.analog.com/opamps.

Products Mentioned in This Article

Product

Description

OP184

Single-Supply Rail-to-Rail Input/Output

Operational Amplifier

OP284

Dual Precision Rail-to-Rail Input/Output

Operational Amplifier

AD8605

Precision, Low Noise, CMOS, Rail-to-Rail

Input/Output Operational Amplifier

ADA4092-4

Micropower, OVP, Rail-to-Rail Input/Output

Operational Amplifier

AD8657

Precision, Micropower 18 V CMOS Rail-to-Rail

Input/Output Operational Amplifier

ABOUT THE AUTHOR

Harry Holt is a staff applications engineer at Analog Devices

(San Jose, CA) in the Precision Amplifiers Group where he

has worked for four years, following 27 years in both field

and factory applications at National Semiconductor for a

variety of products, including data converters, op amps,

references, audio codecs, and FPGAs. He has a BSEE from

San Jose State University and is a life member of Tau Beta Pi

and a Senior Member of the IEEE.

One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com

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