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19-1612; Rev 0; 3/00
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps
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(R) input/output capabilities. These amplifiers provide a 500kHz gain-bandwidth product and 120dB open-loop voltage gain while using only 100A of supply current per amplifier. The combination of low input offset voltage (400V) 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 2k 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 MAX package.
Features
o Ultra-Low Voltage Operation--Guaranteed Down to +1.8V o 100A Supply Current per Amplifier o 500kHz Gain-Bandwidth Product o 120dB Open-Loop Voltage Gain (RL = 100k) o 0.017% THD + Noise at 1kHz o Rail-to-Rail Input Common-Mode Range o Rail-to-Rail Output Drives 2k Load o No Phase Reversal for Overdriven Inputs o Unity-Gain Stable for Capacitive Loads up to 100pF o 400V Input Offset Voltage o Single Available in Ultra-Small 5-Pin SC70 Dual Available in Space-Saving 8-Pin MAX
MAX4291/MAX4292/MAX4294
Applications
2-Cell Battery-Operated Systems Portable Electronic Equipment Battery-Powered Instrumentation Digital Scales Strain Gauges Sensor Amplifiers Cellular Phones
PART MAX4291EXK-T MAX4291EUK-T MAX4292EUA* MAX4292ESA* MAX4294ESD* MAX4294EUD*
Ordering Information
TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 5 SC70-5 5 SOT23-5 8 MAX 8 SO 14 SO 14 TSSOP TOP MARK AAD ADML -- -- -- --
*Future product--contact factory for availability.
Selector Guide
PART MAX4291 MAX4292 MAX4294 AMPLIFIERS PER PACKAGE 1 2 4 PIN-PACKAGE 5-pin SC70/SOT23 8-pin MAX/SO 14-pin SO/TSSOP
VEE 2 IN+ 1 5 VCC
Pin Configurations
TOP VIEW
OUTA
1
8
VCC OUTB INBINB+
MAX4291
INA- 2 INA+ 3 4
MAX4292
7 6 5
IN- 3
4 OUT
VEE
SC70-5/SOT23-5
MAX/SO
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
Pin Configurations continued at end of data sheet. 1
________________________________________________________________ Maxim Integrated Products
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC to VEE) ..................................................+6V All Other Pins ...................................(VCC + 0.3V) to (VEE - 0.3V) Output Short-Circuit Duration.....................................Continuous Continuous Power Dissipation (TA = +70C) 5-Pin SC70 (derate 2.5mW/C above +70C) ................200mW 5-Pin SOT23 (derate 7.1mW/C above +70C)................571mW 8-Pin MAX (derate 4.10mW/C above +70C)..............330mW 8-Pin SO (derate 5.88mW/C above +70C) ..................471mW 14-Pin SO (derate 8.33mW/C above +70C) ................667mW 14-Pin TSSOP (derate 6.3mW/C above +70C) ............500mW Operating Temperature Range............................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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.
ELECTRICAL CHARACTERISTICS
(VCC = +1.8V to +5.5V, VEE = VCM = 0, VOUT = VCC / 2, RL = 100k connected to VCC / 2, TA = +25C, unless otherwise noted.) (Note 1) PARAMETER Supply Voltage Range Quiescent Supply Current (per Amplifier) Input Offset Voltage Input Bias Current Input Offset Current Differential Input Resistance Input Common-Mode Voltage Range SYMBOL VCC IQ VCC = 1.8V VCC = 5.0V MAX4291EXK, MAX4291EUK VOS IB IOS RIN VCM MAX4292EUA, MAX4294EUD MAX4292ESA, MAX4294ESD VCC = 5.0V, 0 VCM 5.0V VCC = 5.0V, 0 VCM 5.0V |VIN+ - VIN-| < 10mV Inferred from CMRR test Tested for 0 VCM 1.8V; VCC = 1.8V Common-Mode Rejection Ratio CMRR Tested for 0 VCM 5.0V, VCC = 5.0V MAX4291EXK, MAX4291EUK MAX4292EUA, MAX4294EUD MAX4292ESA, MAX4294ESD 60 70 70 80 80 80 90 90 90 100 100 100 dB dB MAX4291EXK, MAX4291EUK MAX4292EUA, MAX4294EUD MAX4292ESA, MAX4294ESD 0 50 65 65 80 85 85 dB CONDITIONS Inferred from PSRR test MIN 1.8 100 110 400 400 400 15 1 0.75 VCC TYP MAX 5.5 210 225 2500 1500 1500 55 7 nA nA M V V UNITS V A
MAX4291EXK, MAX4291EUK Power-Supply Rejection Ratio PSRR MAX4292EUA, MAX4294EUD MAX4292ESA, MAX4294ESD
2
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Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps
ELECTRICAL CHARACTERISTICS
(VCC = +1.8V to +5.5V, VEE = VCM = 0, VOUT = VCC / 2, RL = 100k connected to VCC / 2, TA = +25C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS RL = 100k, 0.015V VOUT VCC - 0.015V VCC = 1.8V RL = 2k, 0.1V VOUT VCC - 0.1V Large-Signal Voltage Gain AV RL = 100k, 0.015V VOUT VCC - 0.015V VCC = 5.0V RL = 2k, 0.1V VOUT VCC - 0.1V Output Voltage Swing High Output Voltage Swing Low Output Short-Circuit Current Channel-to-Channel Isolation Gain Bandwidth Product Phase Margin Gain Margin Slew Rate Input Voltage Noise Density Input Current Noise Density Capacitive-Load Stability VOH VOL IOUT(SC) CHISO GBW M GM SR en in f = 10kHz f = 10kHz AVCL = +1V/V, no sustained oscillations Specified as |VCC - VOH| Specified as |VEE - VOL| RL = 100k to VCC / 2 RL = 2k to VCC / 2 RL = 100k to VCC / 2 RL = 2k to VCC / 2 80 120 2 15 3 18 20 100 500 65 12 0.2 70 0.05 100 20 40 15 40 mV mV mA dB kHz degrees dB V/s nV/Hz pA/Hz pF 80 130 80 110 dB MIN 80 TYP 120 MAX UNITS
MAX4291/MAX4292/MAX4294
Sourcing or sinking Specified at f = 10kHz (MAX4292/MAX4294 only)
ELECTRICAL CHARACTERISTICS
(VCC = +1.8V to +5.5V, VEE = VCM = 0, VOUT = VCC / 2, RL = 100k connected to VCC / 2, TA = TMIN to TMAX, unless otherwise noted.) (Note 1) PARAMETER Supply Voltage Range Quiescent Supply Current (per Amplifier) Input Offset Voltage SYMBOL VCC IQ VCC = 1.8V VCC = 5.0V MAX4291EXK, MAX4291EUK VOS MAX4292EUA, MAX4294EUD MAX4292ESA, MAX4294ESD CONDITIONS Inferred from PSRR test MIN 1.8 TYP MAX 5.5 240 270 3000 1500 1500 V UNITS V A
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3
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
ELECTRICAL CHARACTERISTICS
(VCC = +1.8V to +5.5V, VEE = VCM = 0, VOUT = VCC / 2, RL = 100k connected to VCC / 2, TA = TMIN to TMAX, unless otherwise noted.) (Note 1) PARAMETER Input Offset Voltage Drift Input Bias Current Input Offset Current Input Common-Mode Voltage Range SYMBOL TCVOS IB IOS VCM VCC = 5.0V, 0 VCM 5.0V VCC = 5.0V, 0 VCM 5.0V Inferred from CMRR test MAX4291EXK, MAX4291EUK Tested for 0 VCM 1.8V, MAX4292EUA, MAX4294EUD VCC = 1.8V MAX4292ESA, MAX4294ESD Tested for 0 VCM 5.0V, MAX4292EUA, MAX4294EUD VCC = 5.0V MAX4292ESA, MAX4294ESD MAX4291EXK, MAX4291EUK Power-Supply Rejection Ratio PSRR MAX4292EUA, MAX4294EUD MAX4292ESA, MAX4294ESD MAX4294ESD MAX4292ESA, RL = 100k, 0.015V VOUT VCC - 0.015V RL = 2k, 0.1V VOUT VCC - 0.1V RL = 100k, 0.015V VOUT VCC - 0.015V RL = 2k, 0.1V VOUT VCC - 0.1V RL = 100k to VCC / 2 RL = 2k to VCC / 2 RL = 100k to VCC / 2 RL = 2k to VCC / 2 MAX4291EXK, MAX4291EUK 0 50 60 60 60 65 65 78 80 80 80 80 dB 80 80 20 40 15 40 mV mV dB dB dB CONDITIONS MIN TYP 1.2 80 10 VCC MAX UNITS V/C nA nA V
Common-Mode Rejection Ratio
CMRR
VCC = 1.8V Large-Signal Voltage Gain AV VCC = 5.0V
Output Voltage Swing High Output Voltage Swing Low
VOH VOL
Specified as |VCC - VOH| Specified as |VEE - VOL|
Note 1: All devices are 100% tested at TA = +25C. All temperature limits are guaranteed by design.
4
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Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps
Typical Operating Characteristics
(VCC = +2.4V, VEE = VCM = 0, VOUT = VCC / 2, no load, TA = +25C, unless otherwise noted.)
MAX4291/MAX4292/MAX4294
SUPPLY CURRENT PER AMPLIFIER vs. TEMPERATURE
MAX4291 toc01
MINIMUM OPERATING VOLTAGE vs. TEMPERATURE (PSRR 80dB)
MAX4291 toc02
INPUT OFFSET VOLTAGE vs. TEMPERATURE
MAX4291 toc03
160 150 140 SUPPLY CURRENT (A) 130 120 110 100 90 80 70 60 VCC = 1.8V VCC = 5.5V
2.0 MINIMUM OPERATING VOLTAGE (V) 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0
0 -150 VCC = 5.5V -300 -450 -600 -750 -900 VCC = 2.4V VCC = 1.8V
-55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
-55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
INPUT OFFSET VOLTAGE (V)
-55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
INPUT BIAS CURRENT vs. TEMPERATURE
MAX4291 toc04
INPUT BIAS CURRENT vs. COMMON-MODE VOLTAGE (VCC = 1.8V)
MAX4291 toc05
INPUT BIAS CURRENT vs. COMMON-MODE VOLTAGE (VCC = 5.5V)
30 INPUT BIAS CURRENT (nA) 20 10 0 -10 -20 -30 -40
MAX4291 toc06
35 30 INPUT BIAS CURRENT (nA) 25 20 VCC = 5.5V 15 10 5 0 VCC = 1.8V
40 30 INPUT BIAS CURRENT (nA) 20 10 0 -10 -20 -30 -40
40
-55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
-0.5
0
0.5
1.0
1.5
2.0
2.5
-0.5
0.5
1.5
2.5
3.5
4.5
5.5
COMMON-MODE VOLTAGE (V)
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE SWING vs. TEMPERATURE (RL = 100k to VCC / 2)
MAX4291 toc07
OUTPUT VOLTAGE SWING vs. TEMPERATURE (RL = 2k to VCC / 2)
MAX4291 toc08
COMMON-MODE REJECTION RATIO vs. TEMPERATURE
0 VCM VCC VCC = 1.8V -70 -75 CMRR (dB)
MAX4291 toc09
3.5 OUTPUT VOLTAGE SWING (mV) 3.0 2.5 2.0 1.5
VOH = VCC - VOUT VOL = VOUT - VEE VOL (VCC = 5.5V)
35 OUTPUT VOLTAGE SWING (mV) 30 25 20
VOH = VCC - VOUT VOL = VOUT - VEE
-65
VOL (VCC = 5.5V)
VOL (VCC = 1.8V) VOH (VCC = 5.5V)
-80 -85 -90 -95 -100 -105 VCC = 5.5V
15 10 5 0 VOH (VCC = 1.8V)
VOH (VCC = 5.5V) 1.0 0.5 0.0 -55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) VOL (VCC = 1.8V) VOH (VCC = 1.8V)
-55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
-55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
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5
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
Typical Operating Characteristics (continued)
(VCC = +2.4V, VEE = VCM = 0, VOUT = VCC / 2, no load, TA = +25C, unless otherwise noted.)
OPEN-LOOP GAIN vs. OUTPUT SWING LOW (VCC = +1.8V, RL CONNECTED TO VCC)
MAX4291 toc10
OPEN-LOOP GAIN vs. OUTPUT SWING HIGH (VCC = +1.8V, RL CONNECTED TO VEE)
MAX4291 toc11
OPEN-LOOP GAIN vs. OUTPUT SWING LOW (VCC = +5.5V, RL CONNECTED TO VCC)
120 110 RL = 1k GAIN (dB) 100 90 80 RL = 2k
MAX4191 toc12
130 120 110 GAIN (dB) 100 90 80 70 60 50 0 RL = 2k RL = 1k
120 RL = 2k 110 RL = 1k 100 GAIN (dB) 90 80 70 60 50
130
70 60 50 0 50 100 150 200 250 300 350 400 450 500 VOH (mV) 0 50 100 150 200 250 300 350 400 450 500 VOL (mV)
50 100 150 200 250 300 350 400 450 500 VOL (mV)
OPEN-LOOP GAIN vs. OUTPUT SWING HIGH (VCC = +5.5V, RL CONNECTED TO VEE)
MAX4191 toc13
OPEN-LOOP GAIN vs. TEMPERATURE
120 OPEN-LOOP GAIN (dB) 110 100 90 80 70 60 50 VCC = 5.5V -55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) RL = 2k TO VCC RL = 2k TO VEE RL = 1k TO VEE RL = 1k TO VCC
MAX4291 toc14
130 120 110 GAIN (dB) 100 90 80 70 60 50 0
RL = 2k RL = 1k
130
50 100 150 200 250 300 350 400 450 500 VOH (mV)
GAIN AND PHASE vs. FREQUENCY (CL = 0)
60 50 40 30 GAIN (dB) 20 10 0 -10 -20 -30 -40 0.1 1 10 100 1000 FREQUENCY (kHz)
MAX4291 toc15
GAIN AND PHASE vs. FREQUENCY (CL = 100pF)
180 144 108 PHASE (DEGREES) 72 36 0 -36 -72 -108 -144 -180 60 50 40 30 GAIN (dB) 20 10 0 -10 -20 -30 -40 0.1 1 10 100 1000 FREQUENCY (kHz)
MAX4291 toc16
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
144 108 PHASE (DEGREES) THD + NOISE (%) 72 36 0 -36 -72 -108 -144 -180 0.01 0.01 0.1 1 FREQUENCY (kHz) 10 100 VCC = +1.8V RL = 2k Av = +1V/V (NONINVERTING CONFIGURATION)
MAX4291 toc18
AV = +1000V/V
AV = +1000V/V
180
1
0.1 VCC = +5.5V
6
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Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps
Typical Operating Characteristics (continued)
(VCC = +2.4V, VEE = VCM = 0, VOUT = VCC / 2, no load, TA = +25C, unless otherwise noted.)
MAX4291/MAX4292/MAX4294
LOAD RESISTOR vs. CAPACITIVE LOAD
MAX4291 toc19
SMALL-SIGNAL TRANSIENT RESPONSE (NONINVERTING CONFIGURATION)
MAX4291 toc20
SMALL-SIGNAL TRANSIENT RESPONSE (INVERTING CONFIGURATION)
MAX4291 toc21
100
10% OVERSHOOT AV = +1V/V (NONINVERTING CONFIGURATION)
VCC = +2.5V VEE = -2.5V 100mV VCM = 0 IN 0 IN
VCC = +2.5V VEE = -2.5V VCM = 0
100mV
LOAD RESISTOR (k)
10 0
1
VCC = 5.5V VCC = 2.4V 100mV 100mV
0.1 IOUT > 20mA VCC = 5.5V 0.01 0 1 2 3 4 5 6 7 8 9 10 1s/div 1s/div CAPACITIVE LOAD (nF) IOUT > 20mA VCC = 2.4V OUT 0 OUT 0
LARGE-SIGNAL TRANSIENT RESPONSE (NONINVERTING CONFIGURATION)
MAX4291 toc22
LARGE-SIGNAL TRANSIENT RESPONSE (INVERTING CONFIGURATION)
MAX4291 toc23
VCC = +2.5V VEE = -2.5V VCM = 0 IN
+2V IN -2V
VCC = +2.5V VEE = -2.5V VCM = 0
+2V
-2V
+2V
+2V
OUT -2V 10s/div
OUT -2V 10s/div
SUPPLY CURRENT vs. SINK CURRENT
MAX4291/2/4-24
SUPPLY CURRENT vs. SOURCE CURRENT
135 120 SUPPLY CURRENT (A) 105 90 75 60 45 30 VCC = 1.8V VCC = 5.5V VCC = 2.4V
MAX4291/2/4-25
3000 2500 SUPPLY CURRENT (A) 2000 1500 1000 500 0 0 5 10 15 20 25 VCC = 2.4V VCC = 5.5V
150
VCC = 1.8V
15 0 30 0 5 10 15 20 25
SINK CURRENT (mA)
SOURCE CURRENT (mA)
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7
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
Pin Description
PIN MAX4291 1 2 3 4 5 - - - - - - MAX4292 - 4 - - 8 1, 7 2, 6 3, 5 - - - MAX4294 - 11 - - 4 1, 7 2, 6 3, 5 8, 14 9, 13 10, 12 NAME IN+ VEE INOUT VCC OUTA, OUTB INA-, INBINA+, INB+ OUTC, OUTD INC-, INDINC+, IND+ Noninverting Input Negative Supply. Connect to ground for single-supply operation. Inverting Input Amplifier Output Positive Supply Outputs for Amplifiers A and B Inverting Inputs to Amplifiers A and B Noninverting Inputs to Amplifiers A and B Outputs for Amplifiers C and D Inverting Inputs to Amplifiers C and D Noninverting Inputs to Amplifiers C and D FUNCTION
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 VCC and VEE. The input offset voltage is typically 400V. 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.
IN R3
MAX4291 MAX4292 MAX4294
R3 = R1
R2
R1
R2
Figure 1a. Minimizing Offset Error Due to Input Bias Current (Noninverting)
R3
MAX4291 MAX4292 MAX4294
R3 = R1 IN
R2
R1
R2
Figure 1b. Minimizing Offset Error Due to Input Bias Current (Inverting)
8
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Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
Table 1. MAX4291 Characteristics with Typical Battery Systems
BATTERY TYPE RECHARGEABLE No Yes Yes Yes VFRESH (V) 3.0 2.4 3.5 2.4 VEND-OF-LIFE (V) CAPACITY, AA SIZE (mA-h) 2000 750 1000 1000 MAX4291 OPERATING TIME IN NORMAL MODE (h) 20,000 7500 10,000 10,000
Alkaline (2 cells) Nickel-Cadmium (2 cells) Lithium-Ion (1 cell) Nickel-MetalHydride (2 cells)
IN+ 10.6k
1.8 1.8 2.7 1.8
IBIAS =
(VDIFF - 1.8V) 21.2k
IN10.6k
In the region where the differential input voltage approaches 1.8V, the input resistance decreases exponentially from 0.75M to 21.2k 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.
Figure 2. Input Protection Circuit
VCC = +2.5V, VEE = -2.5V IN 2.5V/div 0
Rail-to-Rail Output Stage
The MAX4291/MAX4292/MAX4294 output stage can drive up to a 2k 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 100k load.
OUT 2.5V/div
0
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 100A 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).
20s/div
Figure 3. Rail-to-Rail Input/Output Voltage Range
The MAX4291/MAX4292/MAX4294 family's inputs are protected from large differential input voltages by internal 10.6k 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 0.75M. For differential input voltages greater than 1.8V, input resistance is around 21.2k, and the input bias current can be approximated by the following equation:
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9
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
OFFSET VOLTAGE vs. SUPPLY VOLTAGE
-450 TA = +85C -500 OFFSET VOLTAGE (V) VCM = VCC/2 OUTPUT SOURCE CURRENT (mA) 30 25 20 15 10 5 0 -55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) VCC = 5.5V VOH = 200mV
OUTPUT SOURCE CURRENT vs. TEMPERATURE
VOH = VCC - VOUT VCC = 1.8V VOH = 200mV
-550 TA = +25C -600 TA = -40C
VCC = 5.5V VOH = 100mV VCC = 5.5V VOH = 50mV VCC = 1.8V VOH = 100mV VCC = 1.8V VOH = 50mV
-650
-700 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 SUPPLY VOLTAGE (V)
Figure 4. Offset Voltage vs. Supply Voltage
SUPPLY CURRENT vs. SUPPLY VOLTAGE
140 120 100 80 60 40 20 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 SUPPLY VOLTAGE (V) TA = +25C TA = -40C TA = +85C
Figure 6a. Output Source Current vs. Temperature
OUTPUT SINK CURRENT vs. TEMPERATURE
18 16 OUTPUT SINK CURRENT (mA) 14 12 10 8 6 4 2 0 -55 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) VOL = VOUT - VEE VCC = 5.5V VOL = 200mV V = 5.5V CC VOL = 50mV VCC = 1.8V VOL = 200mV VCC = 5.5V VOL = 100mV VCC = 1.8V VOL = 100mV VCC = 1.8V VOL = 50mV
Figure 5. Supply Current vs. Supply Voltage
SUPPLY CURRENT (A)
Figure 6b. Output Sink Current vs. Temperature
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 2k to V CC /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 = +25C can source 3.5mA to within 100mV of VCC and is capable of driving a 485 load resistor to VEE: RL = (1.8V - 0.1V) = 485 to VEE 3.5mA
The same application can drive a 220k load resistor when terminated in VCC/2 (+0.9V in this case).
10
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Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
100mV
RISO OUT IN
IN 0
MAX4240 MAX4241 MAX4242 MAX4243 MAX4244
RL
CL
OUT
100mV
0
AV =
RL 1 RL + RISO
10s/div VCC = +2.4V, RL = 2k TO VEE, CL = 1000pF, RISO = 100
Figure 7a. Using a Resistor to Isolate a Capacitive Load from the Op Amp
Figure 7c. Pulse Response with Isolating Resistor (100 )
and the VEE supplies should be bypassed to ground with separate 100nF capacitors.
100mV IN 0
100mV
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.
OUT
0
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: V
HYST
10s/div VCC = +2.4V, RL = 2k TO VEE, CL = 1000pF
Figure 7b. Pulse Response Without Isolating Resistor
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.
=V
HI
-V
LO
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
R1 R1 V V = 1 + + HI R2 R REF HYST R1 V =V - V LO HI R CC HYST 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
11
______________________________________________________________________________________
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
PROPAGATION DELAY vs. INPUT OVERDRIVE
1000
INPUT VHI VLO VOH HYSTERESIS
tPD+, VCC = 5.5V tPD (s) tPD-, VCC = 5.5V 100 tPD-, VCC = 1.8V tPD+, VCC = 1.8V
OUTPUT VOL VSIG R1 VCC VOUT RHYST
R2
MAX4291
VREF VEE = GND MAX4292
10 0
10 20 30 40 50 60 VOD (mV)
MAX4294
70 80 90 100
VEE = GND
Figure 8. Propagation Delay vs. Input Overdrive
Figure 9. Hysteresis Comparator Circuit
MAXIMUM SUPPLY CURRENT vs. SUPPLY VOLTAGE
12 MAXIMUM SUPPLY CURRENT (mA) 10 8 6 4 2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 SUPPLY VOLTAGE (V) COMPARATOR CONFIGURATION VIN+ = (VIN-) - 100mV
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 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: R1 VOUT = ILOAD x x R3 R2 For a 1V output and a current load of 50mA, the choice of resistors can be R1 = 2, R2 = 100k, and R3 = 1M.
12
Figure 10. Maximum Supply Current vs. Supply Voltage
______________________________________________________________________________________
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps
ILOAD R1 VCC R2
Pin Configurations (continued)
TOP VIEW
MAX4291/MAX4292/MAX4294
OUTA 1 INA- 2
Q1 VOUT
14 OUTD
MAX4294
13 IND12 IND+ 11 VEE 10 INC+ 9 INC8 OUTC
INA+ 3 VCC 4 INB+ 5
R3
MAX4291
VEE
INB- 6 OUTB 7
Figure 11. Current Monitor for a 2-Cell Battery Stack
TSSOP/SO
Chip Information
MAX4291 TRANSISTOR COUNT: 149 MAX4292 TRANSISTOR COUNT: 356 MAX4294 TRANSISTOR COUNT: 747
______________________________________________________________________________________
13
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
Package Information
SC70, 5L.EPS
14
______________________________________________________________________________________
SOT5L.EPS
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps
Package Information (continued)
8LUMAXD.EPS
MAX4291/MAX4292/MAX4294
Note: The MAX4292 does not have an exposed pad.
SOICN.EPS
______________________________________________________________________________________
15
Ultra-Small, +1.8V, Power, Rail-to-Rail I/O Op Amps MAX4291/MAX4292/MAX4294
Package Information (continued)
TSSOP.EPS
Note: The MAX4294 does not have an exposed pad.
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 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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