General Description
The MAX4291/MAX4292/MAX4294 family of micropow-
er 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 sup-
ply current per amplifier. The combination of low input
offset voltage (±200µV) and high open-loop gain makes
them ideal for low-power/low-voltage, high-precision
portable applications.
The MAX4291/MAX4292/MAX4294 have an input com-
mon-mode range that extends to each supply rail, and
their outputs swing to within 46mV of the rails with a 2kΩ
load. Although the minimum operating voltage is speci-
fied 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-pow-
ered system.
The single MAX4291 is offered in an ultra-small 5-pin
SC70 package. The dual MAX4292 is offered in a
space-saving 8-bump, 1.5mm X 1.5mm footprint, ultra
chip-scale package (UCSP™).
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 (RL= 100kΩ)
♦0.017% Total Harmonic Distortion Plus Noise
(THD + N) at 1kHz
♦Rail-to-Rail Input Common-Mode Range
♦Rail-to-Rail Output Drives 2kΩLoad
♦No Phase Reversal for Overdriven Inputs
♦Unity-Gain Stable for Capacitive Loads up to 100pF
♦200µV Input Offset Voltage (MAX4292/MAX4294)
♦Single in Small 5-Pin SC70
♦Available in Ultra-Small Packages:
5-Pin SC70 (MAX4291)
8-Bump UCSP (MAX4292)
MAX4291/MAX4292/MAX4294
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
________________________________________________________________ Maxim Integrated Products 1
19-1612; Rev 3; 4/02
Pin Configurations
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
UCSP is a trademark of Maxim Integrated Products, Inc.
Ordering Information
Selector Guide
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
PART AMPLIFIERS PIN-PACKAGE
MAX4291 1 5-pin SC70/SOT23
MAX4292 2 8-pin µMAX/SO/UCSP
MAX4294 4 14-pin SO/TSSOP
TOP VIEW
(BUMPS ON BOTTOM)
OUTA VCC OUTB
INA-
INA+
INB-
INB+
VEE
UCSP
MAX4292
Pin Configurations continued at end of data sheet.
*UCSP reliability is integrally linked to the user’s assembly
methods, circuit board material, and environment. Refer to the
UCSP Reliability Notice in the UCSP Reliability section of this
data sheet for more information.
PART TEMP RANGE PIN-
PACKAGE
TOP
MARK
MAX4291EXK-T -40°C to +85°C 5 SC70-5 AAD
MAX4291EUK-T -40°C to +85°C 5 SOT23-5 ADML
MAX4292EBL-T* -40°C to +85°C 8 UCSP-8 AAJ
MAX4292EUA -40°C to +85°C 8 µMAX —
MAX4292ESA -40°C to +85°C 8 SO —
MAX4294ESD -40°C to +85°C 14 SO —
MAX4294EUD -40°C to +85°C 14 TSSOP —
Common-Mode Rejection Ratio
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, VOUT = VCC/2, RL= 100kΩconnected to VCC/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 (VCC to VEE) ....................................................6V
All Other Pins ...................................(VCC + 0.3V) to (VEE - 0.3V)
Current into IN_+, IN_- .....................................................±25mA
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (TA= +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-Bump UCSP (derate 4.7mW/°C above +70°C) ...........379mW
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
MAX4292/MAX4294 ±200 ±1200
VCC = 5.0V, 0 ≤VCM ≤5.0V nA±15 ±60IB
Input Bias Current
VCC = 1.8V
Inferred from PSRR test
Inferred from CMRR test
|VIN+ - VIN-| < 10mV
VCC = 5.0V, 0 ≤VCM ≤5.0V
MAX4291
CONDITIONS
µA
100 210
IQ
V1.8 5.5VCC
Supply Voltage Range
Quiescent Supply Current
(Per Amplifier)
V0V
CC
VCM
Input Common-Mode Voltage
Range
MΩ0.75RIN
Differential Input Resistance
nA±1 ±7IOS
Input Offset Current
µV
±400 ±2500
VOS
Input Offset Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
VCC = 5.0V 100 255
77 100 dBPSRRPower-Supply Rejection Ratio
50 80
dB
Tested for
0 ≤VCM ≤
1.8V;
VCC = 1.8V
CMRRCommon-Mode Rejection Ratio
57 80
60 90
dB
Tested for
0 ≤VCM ≤
5.0V,
VCC = 5.0V
MAX4291
MAX4292/MAX4294
MAX4291
MAX4292/MAX4294 66 90
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, VOUT = VCC/2, RL= 100kΩconnected to VCC/2, TA= TMIN to TMAX, unless otherwise noted.)
(Note 1)
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 1.8V to 5.5V, VEE = VCM = 0, VOUT = VCC/2, RL= 100kΩconnected to VCC/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
CHISO
GBWP
φM
GM
SR
en
in
Specified at f = 10kHz (MAX4292/MAX4294 only)
f = 10kHz
f = 10kHz
AVCL = 1V/V, no sustained oscillations
83
500
65
12
0.2
70
0.05
100 pF
pA/√Hz
nV/√Hz
V/µs
dB
degrees
kHz
dB
mA20Sourcing or sinkingIOUT(SC)
Output Short-Circuit Current
Output-Voltage Swing Low VOL Specified as
|VEE - VOL|RL= 2kΩto VCC/2
RL= 100kΩto VCC/2
46 120
25 80 mV
mV
15 40
220
RL= 2kΩto VCC/2
RL= 100kΩto VCC/2
Specified as
|VCC - VOH|
VOH
Output-Voltage Swing High
Large-Signal Voltage Gain AV
VCC = 5.0V
VCC = 1.8V
RL= 100kΩ,
0.02V ≤VOUT ≤VCC - 0.02V
RL= 2kΩ,
0.1V ≤VOUT ≤VCC - 0.1V
RL= 100kΩ,
0.02V ≤VOUT ≤VCC - 0.02V
RL= 2kΩ,
0.1V ≤VOUT ≤VCC - 0.1V 80 120
80 130
80 110
80 120
dB
UNITSMIN TYP MAXCONDITIONSSYMBOLPARAMETER
270VCC = 5.0V
PARAMETER SYMBOL MIN TYP MAX UNITS
±2000
Input Offset Voltage VOS
±3000 µV
Quiescent Supply Current
(Per Amplifier)
Supply-Voltage Range VCC 1.8 5.5 V
IQ
240 µA
CONDITIONS
MAX4292/MAX4294
MAX4291
Inferred from PSRR test
VCC = 1.8V
80
dB
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.
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 1.8V to 5.5V, VEE = VCM = 0, VOUT = VCC/2, RL= 100kΩconnected to VCC/2, TA= TMIN to TMAX, unless otherwise noted.)
(Note 1)
MAX4291/MAX4292/MAX4294
120RL= 2kΩto VCC/2
RL= 100kΩto VCC/2
RL= 100kΩto VCC/2
80
80
80
VCC = 5.0V
RL= 2kΩ,
0.1V ≤VOUT ≤VCC - 0.1V
RL= 100kΩ,
0.02V ≤VOUT ≤VCC - 0.02V
RL= 2kΩ,
0.1V ≤VOUT ≤VCC - 0.1V
RL= 100kΩ,
0.02V ≤VOUT ≤VCC - 0.02V
PARAMETER SYMBOL MIN TYP MAX UNITS
Large-Signal Voltage Gain AV
80
dB
50
Input Common-Mode Voltage
Range VCM 0V
CC V
Output-Voltage Swing High VOH
20 mV
Output-Voltage Swing Low VOL mV
Input Bias Current
Input Offset Voltage Drift TCVOS 1.2 µV/°C
IB±90 nA
Input Offset Current IOS ±10 nA
CONDITIONS
VCC = 1.8V
Inferred from CMRR test
Specified as
|VCC - VOH|
Specified as
|VEE - VOL|
VCC = 5.0V, 0 ≤VCM ≤5.0V
VCC = 5.0V, 0 ≤VCM ≤5.0V
dB
CMRRCommon-Mode Rejection Ratio
Tested for
0 ≤VCM ≤1.8V,
VCC = 1.8V
75 dBPSRRPower-Supply Rejection Ratio
53
Tested for
0 ≤VCM ≤5.0V,
VCC = 5.0V
60
62
dB
MAX4291
MAX4292/MAX4294
MAX4291
MAX4292/MAX4294
40
RL= 2kΩto VCC/2
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 52035
50 65 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 95 110 125
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 (VCC = 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 (VCC = 5.5V)
MAX4291 toc06
COMMON-MODE VOLTAGE (V)
INPUT BIAS CURRENT (nA)
0
10
5
20
15
25
30
-55 5 35-25 65 95 125
OUTPUT VOLTAGE SWING vs.
TEMPERATURE (RL = 100kΩ TO VCC/2)
MAX4291-07
TEMPERATURE (°C)
OUTPUT VOLTAGE SWING (mV)
VOH = VCC - VOUT
VOL = VOUT - VEE
VOH (VCC = 5.5V OR 1.8V)
VOL (VCC = 5.5V)
VOL (VCC = 1.8V)
0
20
10
40
30
50
60
-55 5 35-25 65 95 125
OUTPUT VOLTAGE SWING vs.
TEMPERATURE (RL = 2kΩ TO VCC/2)
MAX4291-08
TEMPERATURE (°C)
OUTPUT VOLTAGE SWING (mV)
VOH = VCC - VOUT
VOL = VOUT - VEE
VOH (VCC = 1.8V)
VOL (VCC = 5.5V)
VOL (VCC = 1.8V)
VOH (VCC = 5.5V)
-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 ≤ VCM ≤ VCC
Typical Operating Characteristics
(VCC = 2.4V, VEE = VCM = 0, VOUT = VCC/2, no load, TA= +25°C, unless otherwise noted.)
60
80
70
110
100
90
120
130
150
140
160
-55 -25 -10-40 52035
50 65 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, VOUT = VCC/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
(VCC = 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
(VCC = 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
(VCC = 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
(VCC = 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 VCC
RL = 2kΩ TO VEE RL = 1kΩ TO VCC
RL = 1kΩ TO VEE
VCC = 5.5V
60
-40
0.1 1 10 100 1000
GAIN AND PHASE vs. FREQUENCY
(CL = 100pF)
-20
MAX4291 toc17
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
Av = 1V/V
(NONINVERTING
CONFIGURATION)
60
-40
0.1 1 10 100 1000
GAIN AND PHASE vs. FREQUENCY
(CL = 0)
-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)
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)
IOUT > 20mA
VCC = 2.4V
IOUT > 20mA
VCC = 5.5V
VCC = 5.5V
VCC = 2.4V
10% OVERSHOOT
AV = 1V/V
(NONINVERTING CONFIGURATION)
OUT
IN
0
100mV
0
100mV
1µs/div
SMALL-SIGNAL TRANSIENT RESPONSE
(NONINVERTING CONFIGURATION)
MAX4291 toc20
VCC = 2.5V
VEE = -2.5V
VCM = 0
OUT
IN
0
100mV
0
100mV
1µs/div
SMALL-SIGNAL TRANSIENT RESPONSE
(INVERTING CONFIGURATION)
MAX4291 toc21
VCC = 2.5V
VEE = -2.5V
VCM = 0
OUT
IN
-2V
2V
-2V
2V
10µs/div
LARGE-SIGNAL TRANSIENT RESPONSE
(NONINVERTING CONFIGURATION)
MAX4291 toc22
VCC = 2.5V
VEE = -2.5V
VCM = 0
OUT
IN
-2V
2V
-2V
2V
10µs/div
LARGE-SIGNAL TRANSIENT RESPONSE
(INVERTING CONFIGURATION)
MAX4291 toc23
VCC = 2.5V
VEE = -2.5V
VCM = 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)
V
CC
= 5.5V
V
CC
= 2.4V
V
CC
= 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)
V
CC
= 5.5V
V
CC
= 1.8V
V
CC
= 2.4V
Typical Operating Characteristics (continued)
(VCC = 2.4V, VEE = VCM = 0, VOUT = VCC/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 in the smallest
package possible. The input stage consists of separate
NPN and PNP differential stages, which operate togeth-
er to provide a common-mode range extending to both
supply rails. The crossover region of these two pairs
occurs halfway between VCC and VEE. The input offset
voltage is typically ±200µV (MAX4292/MAX4294). 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 common-
mode 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
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
MAX4292
MAX4291 µMAX/SO UCSP MAX4294 NAME FUNCTION
1——— IN+ Noninverting Input
2 4 C2 11 VEE Negative Supply. Connect to ground for
single-supply operation.
3——— IN- Inverting Input
4——— OUT Amplifier Output
5 8 A2 4 VCC Positive Supply
—1, 7 A1, A3 1, 7 OUTA, OUTB Outputs for Amplifiers A and B
—2, 6 B1, B3 2, 6 INA-, INB- Inverting Inputs to Amplifiers A and B
—3, 5 C1, C3 3, 5 INA+, INB+ Noninverting Inputs to Amplifiers A and B
———8, 14 OUTC, OUTD Outputs for Amplifiers C and D
———9, 13 INC-, IND- Inverting Inputs to Amplifiers C and D
———10, 12 INC+, IND+ Noninverting Inputs to Amplifiers C and D
capacitance) creates a parasitic pole that produces an
underdamped signal response. Reducing input capaci-
tance or placing a small capacitor across the feedback
resistor improves response in this case.
The MAX4291/MAX4292/MAX4294 family’s inputs are
protected from large differential input voltages by inter-
nal 10.6kΩseries resistors and back-to-back triple-
diode 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 approximat-
ed by the following equation:
In the region where the differential input voltage
approaches 1.8V, the input resistance decreases expo-
nentially from 0.75MΩto 21.2kΩas 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 triple-
diode stacks.
Rail-to-Rail Output Stage
The MAX4291/MAX4292/MAX4294 output stage can
drive up to a 2kΩload and still swing to within 46mV 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 + 25mV) to (VCC - 2mV) with a 100kΩ
load.
Applications Information
Power-Supply Considerations
The MAX4291/MAX4292/MAX4294 operate from a sin-
gle 1.8V to 5.5V supply (or dual ±0.9V to ±2.75V sup-
plies) and consume only 100µA of supply current per
amplifier. A high power-supply rejection ratio of 100dB
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
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-Metal-
Hydride (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
VEND-OF-LIFE (V)
VFRESH
(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, VEE = -2.5V
Figure 3. Rail-to-Rail Input/Output Voltage Range
10.6kΩ
10.6kΩ
IN-
IN+
Figure 2. Input Protection Circuit
MAX4291/MAX4292/MAX4294
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).
Although the amplifiers are fully guaranteed over tem-
perature 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 cur-
rent 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 2kΩto 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 tem-
perature. 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-sup-
ply rail.
For example, a MAX4291 running from a single 1.8V
supply, operating at TA= +25°C can source 3.5mA to
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
10 ______________________________________________________________________________________
SUPPLY VOLTAGE (V)
-700
-600
-650
-550
-500
-450
0 3.02.52.01.0 1.50.5 3.5 4.0 4.5 5.0 5.5
MAX4291
OFFSET VOLTAGE vs. SUPPLY VOLTAGE
OFFSET VOLTAGE (µV)
TA = +25°C
TA = -40°C
TA = +85°C
V
CM
= V
CC
/
2
Figure 4. Offset Voltage vs. Supply Voltage
0
60
20
40
80
100
120
140
0 2.0 2.5 3.01.00.5 1.5 3.5 4.5 5.04.0 5.5
SUPPLY CURRENT PER AMPLIFIER
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
TA = +85°C
TA = -40°C
TA = +25°C
Figure 5. Supply Current per Amplifier 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)
V
OH
= V
CC
- V
OUT
V
CC
= 5.5V
V
OH
= 200mV
V
CC
= 5.5V
V
OH
= 50mV V
CC
= 1.8V
V
OH
= 100mV
V
CC
= 1.8V
V
OH
= 200mV V
CC
= 5.5V
V
OH
= 100mV
V
CC
= 1.8V
V
OH
= 50mV
Figure 6a. Output Source Current vs. Temperature
V
OL
= 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)
V
CC
= 1.8V
V
OL
= 200mV
V
CC
= 1.8V
V
OL
= 50mV
V
CC
= 5.5V
V
OL
= 200mV
V
CC
= 5.5V
V
OL
= 100mV V
CC
= 1.8V
V
OL
= 100mV
V
CC
= 5.5V
V
OL
= 50mV
Figure 6b. Output Sink Current vs. Temperature
within 100mV of VCC and is capable of driving a 485Ω
load resistor to VEE:
The same application can drive a 220kΩload resistor
when terminated in VCC/2 (0.9V in this case).
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 RISO 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 VCC
and the VEE supplies should be bypassed to ground
with separate 100nF capacitors.
Good PC board layout techniques optimize perfor-
mance 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 excel-
lent 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 cir-
cuit, 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:
R(1.8V 0.1V)
3.5mA 485 to V
LEE
=−= Ω
MAX4291/MAX4292/MAX4294
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
______________________________________________________________________________________ 11
RISO
CL
RL
MAX4291
MAX4292
MAX4294
AV = RL ≈ 1
RL + RISO
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, RL = 2kΩ TO VEE, CL = 1000pF
Figure 7b. Pulse Response Without Isolating Resistor
OUT
IN
0
100mV
0
100mV
10µs/div
VCC = 2.4V, RL = 2kΩ TO VEE, CL = 1000pF, RISO = 100Ω
Figure 7c. Pulse Response with Isolating Resistor (100Ω)
MAX4291/MAX4292/MAX4294
When the output of the comparator is low, the supply
current increases. The output stage has biasing circuit-
ry to monitor the output current. When the amplifier is
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 VCC = 1.8V and to 9mA when
VCC = 5.0V (Figure 10).
Using the MAX4291/MAX4292/MAX4294
as Low-Power Current Monitors
The MAX4291/MAX4292/MAX4294 are ideal for appli-
cations 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 cur-
rent increases, the voltage drop across R1 and R2
increases. Thus, R2 provides a fraction of the load cur-
rent (set by the ratio of R1 and R2) that flows into the
emitter of the PNP transistor. Neglecting PNP base cur-
rent, this current flows into R3, producing a ground-ref-
erenced 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:
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
tPD (µs)
t
PD
+
,
V
CC
= 5.5V
t
PD
-
,
V
CC
= 5.5V
t
PD
+
,
V
CC
= 1.8V
t
PD
-
,
V
CC
= 1.8V
Figure 8. Propagation Delay vs. Input Overdrive
R2
R1
VSIG
OUTPUT
INPUT
VOH
VOL
VEE = GND
VCC
VOUT
RHYST
VEE = GND
MAX4291
MAX4292
MAX4294
HYSTERESIS
VLO
VHI
VREF
Figure 9. Hysteresis Comparator Circuit
0
6
2
4
8
10
12
0 2.0 2.5 3.01.00.5 1.5 3.5 4.5 5.04.0 5.5
MAXIMUM SUPPLY CURRENT PER AMPLIFIER
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
MAXIMUM SUPPLY CURRENT (mA)
COMPARATOR CONFIGURATION
VIN+ = (VIN-) - 100mV
Figure 10. Maximum Supply Current per Amplifier vs. Supply
Voltage
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
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
______________________________________________________________________________________ 13
For a 1V output and a current load of 50mA, the choice
of resistors can be R1 = 2Ω, R2 = 100kΩ, and R3 =
1MΩ.
UCSP Information
Layout Issues
Design the layout for the IC to be as compact as possi-
ble to minimize parasitics. The UCSP uses a bump
pitch of 0.5mm (19.7mil) and bump diameter of 0.3
(~12mil). Therefore, lay out the solder-pad spacing on
0.5mm (19.7mil) centers, using a pad size of 0.25mm
(~10mil) and a solder mask opening of 0.33mm (13mil).
Round or square pads are permissible. Connect multi-
ple vias from the ground plane as close to the ground
pins as possible.
Install capacitors as close as possible to the IC supply
voltage pin. Place the ground end of these capacitors
near the IC GND pins to provide a low-impedance
return path for the signal current.
Prototype Chip Installation
Alignment keys on the PC board, around the area
where the chip is located, will be helpful in the proto-
type assembly process. It is better to align the chip on
the board before any other components are placed,
and then place the board on a hot plate or hot surface
until the solder starts melting. Remove the board from
the hot plate without disturbing the position of the chip
and let it cool down to room temperature before pro-
cessing the board further.
UCSP Reliability
The UCSP represents a unique packaging form factor
that may not perform as well as a packaged product
through traditional mechanical reliability tests. UCSP
reliability is integrally linked to the user’s assembly
methods, circuit board material, and usage environ-
ment. The user should closely review these areas when
considering use of a UCSP.
Performance through operating-life test and moisture
resistance remains uncompromised. The wafer-fabrica-
tion process primarily determines the performance.
Mechanical stress performance is a greater considera-
tion for UCSPs. UCSPs are attached through direct sol-
der contact to the user’s PC board, foregoing the
inherent stress relief of a packaged product lead frame.
Solder-joint contact integrity must be considered.
Comprehensive reliability tests have been performed
and are available upon request. In conclusion, the
UCSP performs reliably through environmental stresses.
Marking Information
R1
ILOAD
R2
VCC
VEE
R3
VOUT
Q1
MAX4291
Figure 11. Current Monitor for a 2-Cell Battery Stack
AAA
AAA
ORIENTATION
PRODUCT ID CODE
LOT CODE
MAX4291/MAX4292/MAX4294
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
14 ______________________________________________________________________________________
VEE
OUT
IN-
15VCC
IN+
SC70/SOT23
TOP VIEW
2
34VEE
OUTB
OUTA
INB-
INB+
VCC
INA+
INA-
µMAX/SO
1
2
8
7
3
4
6
5
MAX4292
MAX4291
OUTA
OUTB
OUTD
OUTC
VCC
INA+
INB+
IND+
INC+
INA-
INB-
IND-
INC-
VEE
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
PROCESS: BiCMOS
MAX4291/MAX4292/MAX4294
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
______________________________________________________________________________________ 15
SOT5L.EPS
SC70, 5L.EPS
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX4291/MAX4292/MAX4294
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
16 ______________________________________________________________________________________
8LUMAXD.EPS
PACKAGE OUTLINE, 8L uMAX/uSOP
1
1
21-0036 J
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
MAX
0.043
0.006
0.014
0.120
0.120
0.198
0.026
0.007
0.037
0.0207 BSC
0.0256 BSC
A2 A1
c
eb
A
L
FRONT VIEW SIDE VIEW
E H
0.6±0.1
0.6±0.1
ÿ 0.50±0.1
1
TOP VIEW
D
8
A2 0.030
BOTTOM VIEW
16∞
S
b
L
H
E
D
e
c
0∞
0.010
0.116
0.116
0.188
0.016
0.005
8
4X S
INCHES
-
A1
A
MIN
0.002
0.950.75
0.5250 BSC
0.25 0.36
2.95 3.05
2.95 3.05
4.78
0.41
0.65 BSC
5.03
0.66
6∞0∞
0.13 0.18
MAX
MIN
MILLIMETERS
- 1.10
0.05 0.15
α
α
DIM
Note: The MAX4292 does not have an exposed pad.
TSSOP.EPS
Note: The MAX4294 does not have an exposed pad.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX4291/MAX4292/MAX4294
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
______________________________________________________________________________________ 17
SOICN.EPS
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
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.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
9LUCSP, 3x3.EPS
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)