Datasheet MAX4294EUD, MAX4292EUA, MAX4292ESA, MAX4291EXK-T, MAX4291EUK-T Datasheet (Maxim)

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MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,

Rail-to-Rail I/O Op Amps

________________________________________________________________ Maxim Integrated Products 1

V

EE

OUTIN-

15V

CC

IN+

SC70-5/SOT23-5

TOP VIEW

2

34

V

EE

OUTB

OUTA

INB-

INB+

V

CC

INA+

INA-

µMAX/SO

1

2

8

7

3

4

6

5

MAX4292

MAX4291

19-1612; Rev 0; 3/00

Pin Configurations

Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.

8 µMAX

5 SOT23-5

5 SC70-5

PIN-

PACKAGE

TEMP. RANGE

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

MAX4292EUA*

MAX4291EUK-T

MAX4291EXK-T

PART

Ordering Information

Selector Guide

—

ADML

AAD

TOP

MARK

14 TSSOP

14 SO

8 SO -40°C to +85°C

-40°C to +85°C

-40°C to +85°CMAX4294EUD*

MAX4294ESD*

MAX4292ESA*

—

—

—

Pin Configurations continued at end of data sheet.

14-pin SO/TSSOP

8-pin µMAX/SO

5-pin SC70/SOT23

PIN-PACKAGE

AMPLIFIERS

PER PACKAGE

1

2

4MAX4294

MAX4292

MAX4291

PART

General Description

The MAX4291/MAX4292/MAX4294 family of micropow­er operational amplifiers operates from a +1.8V to
+5.5V single supply or ±0.9V to ±2.75V dual supplies
and has Rail-to-Rail®input/output capabilities. These
amplifiers provide a 500kHz gain-bandwidth product
and 120dB open-loop voltage gain while using only
100µA of supply current per amplifier. The combination
of low input offset voltage (±400µV) and high-open-loop
gain makes them suitable for low-power/low-voltage
high-precision applications.

The MAX4291/MAX4292/MAX4294 have an input com­mon-mode range that extends to each supply rail, and
their outputs typically swing within 20mV of the rails with
a 2kΩ load. Although the minimum operating voltage is
specified at +1.8V, these devices typically operate down
to +1.5V. The combination of ultra-low-voltage operation,
rail-to-rail inputs/output, and low-power consumption
makes these devices ideal for any portable/two-cell bat­tery-powered system.

The single MAX4291 is offered in an ultra-small 5-pin
SC70 package and the dual MAX4292 is offered in a
space-saving 8-pin µMAX package.

Applications

2-Cell Battery-Operated Systems

Portable Electronic Equipment

Battery-Powered Instrumentation

Digital Scales

Strain Gauges

Sensor Amplifiers

Cellular Phones

Features

♦ Ultra-Low Voltage Operation—Guaranteed Down

to +1.8V

♦ 100µA Supply Current per Amplifier

♦ 500kHz Gain-Bandwidth Product

♦ 120dB Open-Loop Voltage Gain (R

L

= 100kΩ)

♦ 0.017% THD + Noise at 1kHz

♦ Rail-to-Rail Input Common-Mode Range
♦ Rail-to-Rail Output Drives 2kΩ Load

♦ No Phase Reversal for Overdriven Inputs

♦ Unity-Gain Stable for Capacitive Loads up to 100pF

♦ 400µV Input Offset Voltage

♦ Single Available in Ultra-Small 5-Pin SC70

Dual Available in Space-Saving 8-Pin µMAX

*Future product—contact factory for availability.

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,
Rail-to-Rail I/O Op Amps

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +1.8V to +5.5V, VEE= VCM= 0, V

OUT

= V

CC

/ 2, RL= 100kΩ connected to V

CC

/ 2, TA= +25°C, unless otherwise noted.)

(Note 1)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Supply Voltage (VCCto V

EE)

..................................................+6V

All Other Pins ...................................(V

CC

+ 0.3V) to (VEE- 0.3V)

Output Short-Circuit Duration.....................................Continuous

Continuous Power Dissipation (T

A

= +70°C)

5-Pin SC70 (derate 2.5mW/°C above +70°C) ................200mW

5-Pin SOT23 (derate 7.1mW/°C above +70°C)................571mW

8-Pin µMAX (derate 4.10mW/°C above +70°C)..............330mW

8-Pin SO (derate 5.88mW/°C above +70°C) ..................471mW

14-Pin SO (derate 8.33mW/°C above +70°C) ................667mW

14-Pin TSSOP (derate 6.3mW/°C above +70°C) ............500mW

Operating Temperature Range............................-40°C to +85°C

Junction Temperature ......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

80 100

80 100

MAX4292ESA, MAX4294ESD

MAX4292EUA, MAX4294EUD

MAX4291EXK, MAX4291EUK

MAX4292ESA, MAX4294ESD

MAX4292EUA, MAX4294EUD

MAX4291EXK, MAX4291EUK

70 90

70 90

Tested for
0 ≤ V

CM

≤

5.0V,
V

CC

= 5.0V

dB

60 90

65 85

65 85

Common-Mode Rejection Ratio CMRR

Tested for
0 ≤ V

CM

≤

1.8V;
VCC= 1.8V

dB

50 80

Power-Supply Rejection Ratio PSRR dB

80 100MAX4291EXK, MAX4291EUK

V

OS

110 225VCC= 5.0V

PARAMETER SYMBOL MIN TYP MAX UNITS

Input Bias Current I

B

±15 ±55 nA

±400 ±1500

±400 ±1500

Input Offset Voltage

±400 ±2500

µV

Input Offset Current I

OS

±1 ±7 nA

Differential Input Resistance R

IN

0.75 MΩ

Input Common-Mode Voltage
Range

V

CM

0V

CC

V

Quiescent Supply Current
(per Amplifier)

Supply Voltage Range V

CC

1.8 5.5 V

I

Q

100 210

µA

CONDITIONS

VCC= 5.0V, 0 ≤ VCM≤ 5.0V

MAX4292ESA, MAX4294ESD

MAX4292EUA, MAX4294EUD

MAX4291EXK, MAX4291EUK

VCC= 5.0V, 0 ≤ VCM≤ 5.0V

|V

IN+

- V

IN-

| < 10mV

Inferred from CMRR test

Inferred from PSRR test

VCC= 1.8V

MAX4292ESA, MAX4294ESD

MAX4292EUA, MAX4294EUD

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,

Rail-to-Rail I/O Op Amps

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS

(VCC= +1.8V to +5.5V, VEE= VCM= 0, V

OUT

= V

CC

/ 2, RL= 100kΩ connected to V

CC

/ 2, TA= T

MIN

to T

MAX

, unless otherwise

noted.) (Note 1)

ELECTRICAL CHARACTERISTICS

(VCC= +1.8V to +5.5V, VEE= VCM= 0, V

OUT

= V

CC

/ 2, RL= 100kΩ connected to V

CC

/ 2, TA= +25°C, unless otherwise noted.)

(Note 1)

Channel-to-Channel Isolation

Gain Bandwidth Product

Phase Margin

Gain Margin

Slew Rate

Input Voltage Noise Density

Input Current Noise Density

Capacitive-Load Stability

CH

ISO

GBW

φ

M

G

M

SR

e

n

i

n

Specified at f = 10kHz (MAX4292/MAX4294 only)

f = 10kHz

f = 10kHz

A

VCL

= +1V/V, no sustained oscillations

100

500

65

12

0.2

70

0.05

100 pF

pA/√Hz

nV/√Hz

V/µs

dB

degrees

kHz

dB

mA20Sourcing or sinkingI

OUT(SC)

Output Short-Circuit Current

Output Voltage Swing Low V

OL

Specified as
|V

EE

– VOL|

RL= 2kΩ to V

CC

/ 2

RL= 100kΩ to V

CC

/ 2

18 40

315

mV

mV

15 40

220

RL= 2kΩ to V

CC

/ 2

RL= 100kΩ to V

CC

/ 2

Specified as
|V

CC

– VOH|

V

OH

Output Voltage Swing High

Large-Signal Voltage Gain A

V

VCC= 5.0V

VCC= 1.8V

RL= 100kΩ,

0.015V ≤ V

OUT

≤ VCC- 0.015V

RL= 2kΩ,

0.1V ≤ V

OUT

≤ VCC- 0.1V

RL= 100kΩ,

0.015V ≤ V

OUT

≤ VCC- 0.015V

RL= 2kΩ,

0.1V ≤ V

OUT

≤ VCC- 0.1V

80 120

80 130

80 110

80 120

dB

UNITSMIN TYP MAXCONDITIONSSYMBOLPARAMETER

270VCC= 5.0V

PARAMETER SYMBOL MIN TYP MAX UNITS

±1500

±1500

Input Offset Voltage V

OS

±3000

µV

Quiescent Supply Current
(per Amplifier)

Supply Voltage Range V

CC

1.8 5.5 V

I

Q

240

µA

CONDITIONS

MAX4292ESA, MAX4294ESD

MAX4292EUA, MAX4294EUD

MAX4291EXK, MAX4291EUK

Inferred from PSRR test

VCC= 1.8V

MAX4292ESA, MAX4294ESD

Ultra-Small, +1.8V, µPower,
Rail-to-Rail I/O Op Amps

4 _______________________________________________________________________________________

Note 1: All devices are 100% tested at TA= +25°C. All temperature limits are guaranteed by design.

VCC= 5.0V, 0 ≤ VCM≤ 5.0V

VCC= 5.0V, 0 ≤ VCM≤ 5.0V

Specified as
|VEE– VOL|

Specified as
|VCC– VOH|

Inferred from CMRR test

Tested for
0 ≤ VCM≤ 1.8V,
V

CC

= 1.8V

MAX4291EXK, MAX4291EUK

VCC= 1.8V

CONDITIONS

nA±10I

OS

Input Offset Current

nA±80I

B

µV/°C1.2TCV

OS

Input Offset Voltage Drift

Input Bias Current

mV

15

V

OL

Output Voltage Swing Low

mV

20

V

OH

Output Voltage Swing High

V0V

CC

V

CM

Input Common-Mode Voltage
Range

dB

50

CMRRCommon-Mode Rejection Ratio

dB

78

PSRRPower-Supply Rejection Ratio

dB

80

A

V

Large-Signal Voltage Gain

UNITSMIN TYP MAXSYMBOLPARAMETER

MAX4291EXK, MAX4291EUK

MAX4292ESA, MAX4294ESD

MAX4292EUA, MAX4294EUD

MAX4291EXK, MAX4291EUK

MAX4292ESA, MAX4294ESD

MAX4292EUA, MAX4294EUD

Tested for
0 ≤ VCM≤ 5.0V,
VCC= 5.0V

65

65

60

60

60

dB

80

80

RL= 100kΩ,

0.015V ≤ V

OUT

≤ VCC- 0.015V

RL= 2kΩ,

0.1V ≤ V

OUT

≤ VCC- 0.1V

RL= 100kΩ,

0.015V ≤ V

OUT

≤ VCC- 0.015V

RL= 2kΩ,

0.1V ≤ V

OUT

≤ VCC- 0.1V

VCC= 5.0V

80

80

80

RL= 100kΩ to V

CC

/ 2

RL= 100kΩ to V

CC

/ 2

RL= 2kΩ to V

CC

/ 2

RL= 2kΩ to V

CC

/ 2

40

40

ELECTRICAL CHARACTERISTICS

(VCC= +1.8V to +5.5V, VEE= VCM= 0, V

OUT

= V

CC

/ 2, RL= 100kΩ connected to V

CC

/ 2, TA= T

MIN

to T

MAX

, unless otherwise

noted.) (Note 1)

MAX4291/MAX4292/MAX4294

MAX4292ESA, MAX4294ESD

MAX4292EUA, MAX4294EUD

Ultra-Small, +1.8V, µPower,

Rail-to-Rail I/O Op Amps

MAX4291/MAX4292/MAX4294

_______________________________________________________________________________________ 5

1.0

1.2

1.1

1.5

1.4

1.3

1.6

1.7

1.9

1.8

2.0

-55 -25 -10-40

520355065 80 95 110

MINIMUM OPERATING VOLTAGE

vs. TEMPERATURE (PSRR ≥80dB)

MAX4291 toc02

TEMPERATURE (°C)

MINIMUM OPERATING VOLTAGE (V)

125

-900

-600

-750

-300

-450

-150

0

-55 -25 -10 5-40 20 5035 65 80 95 110125

INPUT OFFSET VOLTAGE

vs. TEMPERATURE

MAX4291 toc03

TEMPERATURE (°C)

INPUT OFFSET VOLTAGE (µV)

VCC = 5.5V

VCC = 1.8V

VCC = 2.4V

0

10

5

20

15

30

25

35

-55 -25 -10 5-40 20 35 50 65 80 95 110 125

INPUT BIAS CURRENT

vs. TEMPERATURE

MAX4291 toc04

TEMPERATURE (°C)

INPUT BIAS CURRENT (nA)

VCC = 5.5V

VCC = 1.8V

-40

-30

-20

-10

0

10

20

30

40

-0.5 0.50 1.0 1.5 2.0 2.5

INPUT BIAS CURRENT vs. COMMON-MODE

VOLTAGE (V

CC

= 1.8V)

MAX4291 toc05

COMMON-MODE VOLTAGE (V)

INPUT BIAS CURRENT (nA)

-40

-10

-20

-30

0

10

30

20

40

-0.5 0.5 1.5 2.5 3.5

4.5 5.5

INPUT BIAS CURRENT vs. COMMON-MODE

VOLTAGE (V

CC

= 5.5V)

MAX4291 toc06

COMMON-MODE VOLTAGE (V)

INPUT BIAS CURRENT (nA)

0.0

1.0

0.5

2.0

1.5

3.0

2.5

3.5

-55 -25 -10 5-40 20 35 50 65 80 95 110 125

OUTPUT VOLTAGE SWING vs.

TEMPERATURE (R

L

= 100kΩ to V

CC

/ 2)

MAX4291 toc07

TEMPERATURE (°C)

OUTPUT VOLTAGE SWING (mV)

VOL (VCC = 5.5V)

V

OH

= VCC - V

OUT

V

OL

= V

OUT

- V

EE

VOH (VCC = 5.5V)

VOH (VCC = 1.8V)

VOL (VCC = 1.8V)

0

10

5

20

15

30

25

35

-55 -25 -10 5-40 20 35 50 65 80 95 110 125

OUTPUT VOLTAGE SWING vs.

TEMPERATURE (R

L

= 2kΩ to V

CC

/ 2)

MAX4291 toc08

TEMPERATURE (°C)

OUTPUT VOLTAGE SWING (mV)

VOL (VCC = 5.5V)

V

OH

= VCC - V

OUT

V

OL

= V

OUT

- V

EE

VOH (VCC = 5.5V)

VOH (VCC = 1.8V)

VOL (VCC = 1.8V)

-105

-90

-95

-100

-85

-80

-70

-75

-65

-55 -25 -10-40 5 203550658095110125

COMMON-MODE REJECTION

RATIO vs. TEMPERATURE

MAX4291 toc09

TEMPERATURE (°C)

CMRR (dB)

VCC = 5.5V

VCC = 1.8V

0 ≤ V

CM

≤ V

CC

Typical Operating Characteristics

(VCC= +2.4V, VEE= VCM= 0, V

OUT

= V

CC

/ 2, no load, TA= +25°C, unless otherwise noted.)

60

80

70

110

100

90

120

130

150

140

160

-55 -25 -10-40

520355065 80 95 110

SUPPLY CURRENT PER AMPLIFIER

vs. TEMPERATURE

MAX4291 toc01

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

125

VCC = 5.5V

VCC = 1.8V

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,
Rail-to-Rail I/O Op Amps

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VCC= +2.4V, VEE= VCM= 0, V

OUT

= V

CC

/ 2, no load, TA= +25°C, unless otherwise noted.)

50

70

60

80

110

120

100

90

130

0 100 150 200 25050 300 350 400 450 500

OPEN-LOOP GAIN vs. OUTPUT SWING LOW

(V

CC

= +1.8V, RL CONNECTED TO VCC)

MAX4291 toc10

VOL (mV)

GAIN (dB)

RL = 2kΩ

RL = 1kΩ

50

70

60

90

80

110

100

120

0 200100 300 40050 250150 350 450 500

OPEN-LOOP GAIN vs. OUTPUT SWING HIGH

(V

CC

= +1.8V, RL CONNECTED TO VEE)

MAX4291 toc11

VOH (mV)

GAIN (dB)

RL = 2kΩ

RL = 1kΩ

50

70

60

80

110

120

100

90

130

0 100 150 200 25050 300 350 400 450 500

OPEN-LOOP GAIN vs. OUTPUT SWING LOW

(V

CC

= +5.5V, RL CONNECTED TO VCC)

MAX4191 toc12

VOL (mV)

GAIN (dB)

RL = 2kΩ

RL = 1kΩ

50

70

60

80

110

120

100

90

130

0 100 150 200 25050 300 350 400 450 500

OPEN-LOOP GAIN vs. OUTPUT SWING HIGH

(V

CC

= +5.5V, RL CONNECTED TO VEE)

MAX4191 toc13

VOH (mV)

GAIN (dB)

RL = 2kΩ

RL = 1kΩ

50

80

70

60

90

100

120

110

130

-55 -25 -10-40 5 203550658095110125

OPEN-LOOP GAIN vs. TEMPERATURE

MAX4291 toc14

TEMPERATURE (°C)

OPEN-LOOP GAIN (dB)

RL = 2kΩ TO V

CC

RL = 2kΩ TO V

EE

RL = 1kΩ TO V

CC

RL = 1kΩ TO V

EE

VCC = 5.5V

60

-40

0.1 1 10 100 1000

GAIN AND PHASE vs. FREQUENCY

(C

L

= 0)

-20

MAX4291 toc15

FREQUENCY (kHz)

GAIN (dB)

0

20

40

30

10

-10

-30

50

AV = +1000V/V

180

144

108

72

36

0

-36

-72

-108

-144

-180

PHASE (DEGREES)

60

-40

0.1 1 10 100 1000

GAIN AND PHASE vs. FREQUENCY

(C

L

= 100pF)

-20

MAX4291 toc16

FREQUENCY (kHz)

GAIN (dB)

0

20

40

30

10

-10

-30

50

AV = +1000V/V

180

144

108

72

36

0

-36

-72

-108

-144

-180

PHASE (DEGREES)

1

0.01

0.01 10 100

0.1

FREQUENCY (kHz)

THD + NOISE (%)

10.1

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

VCC = +5.5V

VCC = +1.8V

MAX4291 toc18

RL = 2kΩ

A

v

= +1V/V
(NONINVERTING
CONFIGURATION)

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,

Rail-to-Rail I/O Op Amps

_______________________________________________________________________________________ 7

0.01

0.1

10

1

100

0 23451 678910

LOAD RESISTOR vs. CAPACITIVE LOAD

MAX4291 toc19

CAPACITIVE LOAD (nF)

LOAD RESISTOR (kΩ)

I

OUT

> 20mA

V

CC

= 2.4V

I

OUT

> 20mA

V

CC

= 5.5V

VCC = 5.5V

VCC = 2.4V

10% OVERSHOOT
A

V

= +1V/V

(NONINVERTING CONFIGURATION)

OUT

IN

0

100mV

0

100mV

1µs/div

SMALL-SIGNAL TRANSIENT RESPONSE

(NONINVERTING CONFIGURATION)

MAX4291 toc20

VCC = +2.5V
V

EE

= -2.5V

V

CM

= 0

OUT

IN

0

100mV

0

100mV

1µs/div

SMALL-SIGNAL TRANSIENT RESPONSE

(INVERTING CONFIGURATION)

MAX4291 toc21

VCC = +2.5V
V

EE

= -2.5V

V

CM

= 0

OUT

IN

-2V

+2V

-2V

+2V

10µs/div

LARGE-SIGNAL TRANSIENT RESPONSE

(NONINVERTING CONFIGURATION)

MAX4291 toc22

VCC = +2.5V
V

EE

= -2.5V

V

CM

= 0

OUT

IN

-2V

+2V

-2V

+2V

10µs/div

LARGE-SIGNAL TRANSIENT RESPONSE

(INVERTING CONFIGURATION)

MAX4291 toc23

VCC = +2.5V
V

EE

= -2.5V

V

CM

= 0

0

1000

500

2000

1500

2500

3000

010155 202530

SUPPLY CURRENT vs. SINK CURRENT

MAX4291/2/4-24

SINK CURRENT (mA)

SUPPLY CURRENT (µA)

VCC = 5.5V

VCC = 2.4V

VCC = 1.8V

0

60

45

30

15

105

90

75

120

135

150

0105152025

SUPPLY CURRENT vs. SOURCE CURRENT

MAX4291/2/4-25

SOURCE CURRENT (mA)

SUPPLY CURRENT (µA)

VCC = 5.5V

VCC = 1.8V

VCC = 2.4V

Typical Operating Characteristics (continued)

(VCC= +2.4V, VEE= VCM= 0, V

OUT

= V

CC

/ 2, no load, TA= +25°C, unless otherwise noted.)

Detailed Description

Rail-to-Rail Input Stage

The MAX4291/MAX4292/MAX4294 have rail-to-rail
inputs and output stages that are specifically designed
for low-voltage, single-supply operation. The input
stage consists of separate NPN and PNP differential
stages, which operate together to provide a common­mode range extending to both supply rails. The
crossover region of these two pairs occurs halfway
between VCCand VEE. The input offset voltage is typi­cally ±400µV. Low operating supply voltage, low sup­ply current, rail-to-rail common-mode input range, and
rail-to-rail outputs make this family of operational ampli­fiers (op amps) an excellent choice for precision or
general-purpose, low-voltage, battery-powered sys­tems.

Since the input stage consists of NPN and PNP pairs,
the input bias current changes polarity as the common­mode voltage passes through the crossover region.
Match the effective impedance seen by each input to
reduce the offset error caused by input bias currents
flowing through external source impedances (Figures
1a and 1b).

The combination of high source impedance plus input
capacitance (amplifier input capacitance plus stray
capacitance) creates a parasitic pole that produces an
underdamped signal response. Reducing input capaci­tance or placing a small capacitor across the feedback
resistor improves response in this case.

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,
Rail-to-Rail I/O Op Amps

8 _______________________________________________________________________________________

Pin Description

R3

IN

R3 = R1 R2

R1 R2

MAX4291
MAX4292
MAX4294

R3

R3 = R1 R2

R1 R2

MAX4291
MAX4292
MAX4294

IN

Figure 1a. Minimizing Offset Error Due to Input Bias Current
(Noninverting)

Figure 1b. Minimizing Offset Error Due to Input Bias Current
(Inverting)

PIN

NAME

IN+

V

EE

OUTA, OUTB

V

CC

OUT

IN-

INC+, IND+

INC-, IND-

OUTC, OUTD

INA+, INB+

INA-, INB-

MAX4294

–

11

1, 7

4

–

–

10, 12

9, 13

8, 14

3, 5

2, 6

FUNCTION

MAX4291

MAX4292

1 – Noninverting Input

2 4 Negative Supply. Connect to ground for single-supply operation.

– 1, 7 Outputs for Amplifiers A and B

5 8 Positive Supply

4 – Amplifier Output

3 – Inverting Input

– – Noninverting Inputs to Amplifiers C and D

– – Inverting Inputs to Amplifiers C and D

– – Outputs for Amplifiers C and D

– 3, 5 Noninverting Inputs to Amplifiers A and B

– 2, 6 Inverting Inputs to Amplifiers A and B

The MAX4291/MAX4292/MAX4294 family’s inputs are
protected from large differential input voltages by inter­nal 10.6kΩ series resistors and back-to-back triple­diode stacks across the inputs (Figure 2). For
differential input voltages (much less than 1.8V), input
resistance is typically 0.75MΩ. For differential input
voltages greater than 1.8V, input resistance is around

21.2kΩ, and the input bias current can be approximat­ed by the following equation:

In the region where the differential input voltage
approaches 1.8V, the input resistance decreases expo­nentially from 0.75MΩ to 21.2kΩ as the diode block
begins to conduct. Conversely, the bias current
increases with the same curve.

In unity-gain configuration, high slew rate input signals
may capacitively couple to the output through the triple­diode stacks.

Rail-to-Rail Output Stage

The MAX4291/MAX4292/MAX4294 output stage can
drive up to a 2kΩ load and still swing to within 20mV of
the rails. Figure 3 shows the output voltage swing of a
MAX4291 configured as a unity-gain buffer, powered
from a ±2.5V supply. The output for this setup typically
swings from (VEE+ 3mV) to (VCC- 2mV) with a 100kΩ
load.

Applications Information

Power-Supply Considerations

The MAX4291/MAX4292/MAX4294 operate from a sin­gle +1.8V to +5.5V supply (or dual ±0.9V to ±2.75V
supplies) and consume only 100µA of supply current
per amplifier. A high power-supply rejection ratio of
80dB allows the amplifiers to be powered directly off a
decaying battery voltage, simplifying design and
extending battery life.

The MAX4291/MAX4292/MAX4294 are ideally suited for
use with most battery-powered systems. Table 1 lists a
variety of typical battery types showing voltage when
fresh, voltage at end-of-life, capacity, and approximate
operating time from a MAX4291 (assuming nominal
conditions).

I

(V - 1.8V)

21.2k

BIAS

DIFF

=

Ω

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,

Rail-to-Rail I/O Op Amps

_______________________________________________________________________________________ 9

Table 1. MAX4291 Characteristics with Typical Battery Systems

750Yes

Nickel-Cadmium
(2 cells)

1000Yes

Lithium-Ion
(1 cell)

1000Yes

Nickel-Metal­Hydride (2 cells)

2000NoAlkaline (2 cells)

BATTERY TYPE

CAPACITY, AA SIZE

(mA-h)

2.4

3.5

2.4

3.0

1.8

2.7

1.8

1.8

V

END-OF-LIFE

(V)

V

FRESH

(V)

RECHARGE-

ABLE

7500

10,000

10,000

20,000

MAX4291

OPERATING TIME IN

NORMAL MODE

(h)

OUT

2.5V/div

IN

2.5V/div

0

0

20µs/div

VCC = +2.5V, V

EE

= -2.5V

Figure 3. Rail-to-Rail Input/Output Voltage Range

10.6k

10.6k

IN-

IN+

Figure 2. Input Protection Circuit

MAX4291/MAX4292/MAX4294

Although the amplifiers are fully guaranteed over tem­perature for operation down to a +1.8V single supply,
even lower voltage operation is possible in practice.
Figures 4 and 5 show the offset voltage and supply cur­rent as a function of supply voltage and temperature.

Load-Driving Capability

The MAX4291/MAX4292/MAX4294 are fully guaranteed
over temperature and supply voltage range to drive a
maximum resistive load of 2kΩ to VCC/2, although
heavier loads can be driven in many applications. The
rail-to-rail output stage of the amplifier can be modeled
as a current source when driving the load toward VCC,
and as a current sink when driving the load toward VEE.
The limit of this current source/sink varies with supply
voltage, ambient temperature, and lot-to-lot variations
of the units.

Figures 6a and 6b show the typical current source and
sink capabilities of the MAX4291/MAX4292/MAX4294
family as a function of supply voltage and ambient tem­perature. The contours on the graph depict the output
current value, based on driving the output voltage to
within 50mV, 100mV, and 200mV of either power-sup­ply rail.

For example, a MAX4291 running from a single +1.8V
supply, operating at TA= +25°C can source 3.5mA to
within 100mV of VCCand is capable of driving a 485Ω
load resistor to VEE:

The same application can drive a 220kΩ load resistor
when terminated in VCC/2 (+0.9V in this case).

R

(1.8V 0.1V)

3.5mA

485 to V

LEE

=

−=

Ω

Ultra-Small, +1.8V, µPower,
Rail-to-Rail I/O Op Amps

10 ______________________________________________________________________________________

SUPPLY VOLTAGE (V)

-700

-600

-650

-550

-500

-450

032.521 1.50.5 3.5 4 4.5 5 5.5

OFFSET VOLTAGE vs. SUPPLY VOLTAGE

OFFSET VOLTAGE (µV)

TA = +25°C

TA = -40°C

TA = +85°C

VCM = VCC/

2

Figure 4. Offset Voltage vs. Supply Voltage

0

60

20

40

80

100

120

140

0 2 2.5 310.5 1.5 3.5 4.5 54 5.5

SUPPLY CURRENT vs. SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

TA = +85°C

TA = -40°C

TA = +25°C

Figure 5. Supply Current vs. Supply Voltage

0

15

5

10

20

25

30

-55 5 20 35-25-40 -10 50 80 1109565 125

OUTPUT SOURCE CURRENT

vs. TEMPERATURE

TEMPERATURE (°C)

OUTPUT SOURCE CURRENT (mA)

VOH = V

CC

- V

OUT

VCC = 5.5V
V

OH

= 200mV

VCC = 5.5V
V

OH

= 50mV

VCC = 1.8V
V

OH

= 100mV

VCC = 1.8V
V

OH

= 200mV

VCC = 5.5V
V

OH

= 100mV

VCC = 1.8V
V

OH

= 50mV

Figure 6a. Output Source Current vs. Temperature

VOL = V

OUT

- V

EE

0

10

2

4

6

8

12

14

16

18

-55 5 20 35-25-40 -10 50 80 1109565 125

OUTPUT SINK CURRENT

vs. TEMPERATURE

TEMPERATURE (°C)

OUTPUT SINK CURRENT (mA)

VCC = 1.8V
V

OL

= 200mV

VCC = 1.8V
V

OL

= 50mV

VCC = 5.5V
V

OL

= 200mV

VCC = 5.5V
V

OL

= 100mV

VCC = 1.8V
V

OL

= 100mV

VCC = 5.5V
V

OL

= 50mV

Figure 6b. Output Sink Current vs. Temperature

Driving Capacitive Loads

The MAX4291/MAX4292/MAX4294 are unity-gain stable
for loads up to 100pF (see the Load Resistor vs.
Capacitive Load graph in the Typical Operating
Characteristics). Applications that require greater
capacitive drive capability should use an isolation
resistor between the output and the capacitive load
(Figure 7). Note that this alternative results in a loss of
gain accuracy because R

ISO

forms a voltage divider

with the load resistor.

Power-Supply Bypassing and Layout

The MAX4291/MAX4292/MAX4294 family operates from
either a single +1.8V to +5.5V supply or dual ±0.9V to
±2.75V supplies. For single-supply operation, bypass
the power supply with a 100nF capacitor to VEE(in this
case GND). For dual-supply operation, both the V

CC

and the VEEsupplies should be bypassed to ground
with separate 100nF capacitors.

Good PC board layout techniques optimize perfor­mance by decreasing the amount of stray capacitance
at the op amp’s inputs and output. To decrease stray
capacitance, minimize trace lengths and widths by
placing external components as close as possible to
the op amp. Surface-mount components are an excel­lent choice.

Using the MAX4291/MAX4292/MAX4294

as Comparators

Although optimized for use as operational amplifiers,
the MAX4291/MAX4292/MAX4294 can also be used as
rail-to-rail I/O comparators. Typical propagation delay
depends on the input overdrive voltage, as shown in
Figure 8. External hysteresis can be used to minimize
the risk of output oscillation. The positive feedback cir­cuit, shown in Figure 9, causes the input threshold to
change when the output voltage changes state. The
two thresholds create a hysteresis band that can be
calculated by the following equations:

When the output of the comparator is low, the supply
current increases. The output stage has biasing circuit­ry to monitor the output current. When the amplifier is

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,

Rail-to-Rail I/O Op Amps

______________________________________________________________________________________ 11

R

ISO

C

L

R

L

MAX4240
MAX4241
MAX4242
MAX4243
MAX4244

AV =

R

L

≈ 1

R

L

+ R

ISO

OUT

IN

Figure 7a. Using a Resistor to Isolate a Capacitive Load from
the Op Amp

OUT

IN

0

100mV

0

100mV

10µs/div

VCC = +2.4V, R

L

= 2kΩ TO V

EE, CL

= 1000pF

Figure 7b. Pulse Response Without Isolating Resistor

OUT

IN

0

100mV

0

100mV

10µs/div

VCC = +2.4V, R

L

= 2kΩ TO V

EE

, CL = 1000pF, R

ISO

= 100Ω

Figure 7c. Pulse Response with Isolating Resistor (100 Ω)

V V V

V 1

R1
R2

R1

R

V

V V

R1

R

V

HYST HI LO

HI

HYST

REF

LO HI

HYST

CC

=−

=+ +















=−















MAX4291/MAX4292/MAX4294

used as a comparator, the output stage is overdriven
and the current through the biasing circuitry increases
to maximum. For the MAX4291, typical supply currents
increase to 1.5mA with V

CC

= 1.8V and to 9mA when

V

CC

= 5.0V (Figure 10).

Using the MAX4291/MAX4292/MAX4294

as Low-Power Current Monitors

The MAX4291/MAX4292/MAX4294 are ideal for appli­cations powered from a two-cell battery stack. Figure
11 shows an application circuit in which the MAX4291
is used for monitoring the current of a two-cell battery
stack. In this circuit, a current load is applied, and the
voltage drop at the battery terminal is sensed.

The voltage on the load side of the battery stack is
equal to the voltage at the emitter of Q1 due to the
feedback loop containing the op amp. As the load cur­rent increases, the voltage drop across R1 and R2
increases. Thus, R2 provides a fraction of the load cur­rent (set by the ratio of R1 and R2) that flows into the
emitter of the PNP transistor. Neglecting PNP base cur­rent, this current flows into R3, producing a ground-ref­erenced voltage proportional to the load current. To
minimize errors, scale R1 to give a voltage drop that is
large enough in comparison to the op amp’s VOS.

Calculate the output voltage of the application using
the following equation:

For a 1V output and a current load of 50mA, the choice
of resistors can be R1 = 2Ω, R2 = 100kΩ, and R3 =
1MΩ.

VI

R1

R2

R3

OUT LOAD

=×

























×

Ultra-Small, +1.8V, µPower,
Rail-to-Rail I/O Op Amps

12 ______________________________________________________________________________________

06090

20 30

10

40 50 8070 100

PROPAGATION DELAY
vs. INPUT OVERDRIVE

VOD (mV)

10

100

1000

t

PD

(µs)

tPD+, VCC = 5.5V

tPD-, VCC = 5.5V

tPD+, VCC = 1.8V

tPD-, VCC = 1.8V

Figure 8. Propagation Delay vs. Input Overdrive

R2

R1

V

SIG

OUTPUT

INPUT

V

OH

V

OL

V

EE

= GND

V

CC

V

OUT

R

HYST

V

EE

= GND

MAX4291
MAX4292
MAX4294

HYSTERESIS

V

LO

V

HI

V

REF

Figure 9. Hysteresis Comparator Circuit

0

6

2

4

8

10

12

0 2 2.5 310.5 1.5 3.5 4.5 54 5.5

MAXIMUM SUPPLY CURRENT

vs. SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

MAXIMUM SUPPLY CURRENT (mA)

COMPARATOR CONFIGURATION
V

IN+

= (VIN-) - 100mV

Figure 10. Maximum Supply Current vs. Supply Voltage

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,

Rail-to-Rail I/O Op Amps

______________________________________________________________________________________ 13

R1

I

LOAD

R2

V

CC

V

EE

R3

V

OUT

Q1

MAX4291

Figure 11. Current Monitor for a 2-Cell Battery Stack

TOP VIEW

OUTA

OUTB

OUTD

OUTC

V

CC

INA+

INB+

IND+

INC+

INA-

INB-

IND-

INC-

V

EE

1

5

6

7

MAX4294

TSSOP/SO

2

3

4

14

10

9

8

13

12

11

Pin Configurations (continued)

Chip Information

MAX4291 TRANSISTOR COUNT: 149

MAX4292 TRANSISTOR COUNT: 356

MAX4294 TRANSISTOR COUNT: 747

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,
Rail-to-Rail I/O Op Amps

14 ______________________________________________________________________________________

Package Information

SC70, 5L.EPS

SOT5L.EPS

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,

Rail-to-Rail I/O Op Amps

______________________________________________________________________________________ 15

Package Information (continued)

8LUMAXD.EPS

SOICN.EPS

Note: The MAX4292 does not have an exposed pad.

MAX4291/MAX4292/MAX4294

Ultra-Small, +1.8V, µPower,
Rail-to-Rail I/O Op Amps

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Package Information (continued)

TSSOP.EPS

Note: The MAX4294 does not have an exposed pad.