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19-0265; Rev 2; 9/96
Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps
_______________General Description
The dual MAX492, quad MAX494, and single MAX495 operational amplifiers combine excellent DC accuracy with rail-to-rail operation at the input and output. Since the common-mode voltage extends from VCC to VEE, the devices can operate from either a single supply (+2.7V to +6V) or split supplies (1.35V to 3V). Each op amp requires less than 150A supply current. Even with this low current, the op amps are capable of driving a 1k load, and the input referred voltage noise is only 25nV/Hz. In addition, these op amps can drive loads in excess of 1nF. The precision performance of the MAX492/MAX494/ MAX495, combined with their wide input and output dynamic range, low-voltage single-supply operation, and very low supply current, makes them an ideal choice for battery-operated equipment and other low-voltage applications. The MAX492/MAX494/MAX495 are available in DIP and SO packages in the industry-standard op-amp pin configurations. The MAX495 is also available in the smallest 8-pin SO: the MAX package.
____________________________Features
o o o o o o o o o o o o o Low-Voltage Single-Supply Operation (+2.7V to +6V) Rail-to-Rail Input Common-Mode Voltage Range Rail-to-Rail Output Swing 500kHz Gain-Bandwidth Product Unity-Gain Stable 150A Max Quiescent Current per Op Amp No Phase Reversal for Overdriven Inputs 200V Offset Voltage High Voltage Gain (108dB) High CMRR (90dB) and PSRR (110dB) Drives 1k Load Drives Large Capacitive Loads MAX495 Available in MAX Package--8-Pin SO
MAX492/MAX494/MAX495
______________Ordering Information
PART MAX492CPA MAX492CSA MAX492C/D MAX492EPA MAX492ESA MAX492MJA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 8 SO Dice* 8 Plastic DIP 8 SO 8 CERDIP
________________________Applications
Portable Equipment Battery-Powered Instruments Data Acquisition Signal Conditioning Low-Voltage Applications
Ordering Information continued at end of data sheet. *Dice are specified at TA = +25C, DC parameters only.
__________Typical Operating Circuit
_________________Pin Configurations
TOP VIEW
+5V 1 VDD 10k 2
OUT1 1 IN1- 2 IN1+ 3
8 7 6
VCC OUT2 IN2IN2+
7 6 2
MAX187 (ADC)
AIN
VEE 4 SERIAL INTERFACE NULL 1 4.096V IN1- 2 IN1+ 3 VEE 4
ANALOG INPUT 10k
3
MAX495
4
DOUT 6 8 SCLK 7 CS
MAX492
DIP/SO
5
3 SHDN 4 REF GND 5
8
N.C. VCC OUT NULL
MAX495
7 6 5
DIP/SO/MAX
INPUT SIGNAL CONDITIONING FOR LOW-VOLTAGE ADC
Pin Configurations continued at end of data sheet.
1
________________________________________________________________ Maxim Integrated Products
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Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC to VEE) ....................................................7V Common-Mode Input Voltage..........(VCC + 0.3V) to (VEE - 0.3V) Differential Input Voltage .........................................(VCC - VEE) Input Current (IN+, IN-, NULL1, NULL2) ..........................10mA Output Short-Circuit Duration ....................Indefinite short circuit to either supply Voltage Applied to NULL Pins ....................................VCC to VEE Continuous Power Dissipation (TA = +70C) 8-Pin Plastic DIP (derate 9.09mW/C above +70C) ....727mW 8-Pin SO (derate 5.88mW/C above +70C).................471mW 8-Pin CERDIP (derate 8.00mW/C above +70C).........640mW 8-Pin MAX (derate 4.1mW/C above +70C) ..............330mW 14-Pin Plastic DIP (derate 10.00mW/C above +70C)...800mW 14-Pin SO (derate 8.33mW/C above +70C)...............667mW 14-Pin CERDIP (derate 9.09mW/C above +70C).......727mW Operating Temperature Ranges MAX49_C_ _ ........................................................0C to +70C MAX49_E_ _......................................................-40C to +85C MAX49_M_ _ ...................................................-55C to +125C Junction Temperatures MAX49_C_ _/E_ _..........................................................+150C MAX49_M_ _ .................................................................+175C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+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.
DC ELECTRICAL CHARACTERISTICS
(VCC = 2.7V to 6V, VEE = GND, VCM = 0V, VOUT = VCC / 2, TA = +25C, unless otherwise noted.) PARAMETER Input Offset Voltage Input Bias Current Input Offset Current Differential Input Resistance Common-Mode Input Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio CONDITIONS VCM = VEE to VCC VCM = VEE to VCC VCM = VEE to VCC MIN TYP 200 25 0.5 2 VEE - 0.25 (VEE - 0.25V) VCM (VCC + 0.25V) VCC = 2.7V to 6V VCC = 2.7V, RL = 100k, VOUT = 0.25V to 2.45V VCC = 2.7V, RL = 1k, VOUT = 0.5V to 2.2V VCC = 5.0V, RL = 100k, VOUT = 0.25V to 4.75V VCC = 5.0V, RL = 1k, VOUT = 0.5V to 4.5V RL = 100k RL = 1k Output Short-Circuit Current Operating Supply Voltage Range Supply Current (per amplifier) VCM = VOUT = VCC / 2 VCC = 2.7V VCC = 5V 2.7 135 150 Sourcing Sinking Sourcing Sinking Sourcing Sinking Sourcing Sinking VOH VOL VOH VOL VCC - 0.20 74 88 90 90 94 78 98 92 98 86 90 110 104 102 105 90 108 100 110 98 VEE + 0.04 VEE + 0.075 VCC - 0.15 VEE + 0.15 VEE + 0.20 30 6.0 150 170 mA V A dB VCC + 0.25 MAX 500 60 6 UNITS V nA nA M V dB dB
Large-Signal Voltage Gain (Note 1)
VCC - 0.075 VCC - 0.04 V
Output Voltage Swing (Note 1)
2
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Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps
AC ELECTRICAL CHARACTERISTICS
(VCC = 2.7V to 6V, VEE = GND, TA = +25C, unless otherwise noted.) PARAMETER Gain-Bandwidth Product Phase Margin Gain Margin Total Harmonic Distortion Slew Rate Time Turn-On Time Input Noise-Voltage Density Input Noise-Current Density Amp-Amp Isolation CONDITIONS RL = 100k, CL = 100pF RL = 100k, CL = 100pF RL = 100k, CL = 100pF RL = 10k, CL = 15pF, VOUT = 2Vp-p, AV = +1, f = 1kHz RL = 100k, CL = 15pF To 0.1%, 2V step VCC = 0V to 3V step, VIN = VCC / 2, AV = +1 f = 1kHz f = 1kHz f = 1kHz MIN TYP 500 60 10 0.003 0.20 12 5 25 0.1 125 MAX UNITS kHz degrees dB % V/s s s nV/Hz pA/Hz dB
MAX492/MAX494/MAX495
DC ELECTRICAL CHARACTERISTICS
(VCC = 2.7V to 6V, VEE = GND, VCM = 0V, VOUT = VCC / 2, TA = 0C to +70C, unless otherwise noted.) PARAMETER Input Offset Voltage Input Offset Voltage Tempco Input Bias Current Input Offset Current Common-Mode Input Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio VCM = VEE to VCC VCM = VEE to VCC VEE - 0.20 (VEE - 0.20) VCM (VCC + 0.20) VCC = 2.7V to 6V VCC = 2.7V, RL = 100k, VOUT = 0.25V to 2.45V Large-Signal Voltage Gain (Note 1) VCC = 2.7V, RL = 1k, VOUT = 0.5V to 2.2V VCC = 5.0V, RL = 100k, VOUT = 0.25V to 4.75V VCC = 5.0V, RL = 1k, VOUT = 0.5V to 4.5V Output Voltage Swing (Note 1) Operating Supply Voltage Range Supply Current (per amplifier) VCM = VOUT = VCC / 2 VCC = 2.7V VCC = 5V RL = 100k RL = 1k Sourcing Sinking Sourcing Sinking Sourcing Sinking Sourcing Sinking VOH VOL VOH VOL 2.7 VCC - 0.20 VEE + 0.20 6.0 175 190 V A 72 86 88 84 92 76 92 88 96 82 VCC - 0.075 VEE + 0.075 V dB VCM = VEE to VCC 2 75 6 VCC + 0.20 CONDITIONS MIN TYP MAX 650 UNITS V V/C nA nA V dB dB
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3
Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
DC ELECTRICAL CHARACTERISTICS
(VCC = 2.7V to 6V, VEE = GND, VCM = 0V, VOUT = VCC / 2, TA = -40C to +85C, unless otherwise noted.) PARAMETER Input Offset Voltage Input Offset Voltage Tempco Input Bias Current Input Offset Current Common-Mode Input Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio VCM = VEE to VCC VCM = VEE to VCC VEE - 0.15 (VEE - 0.15) VCM (VCC + 0.15) VCC = 2.7V to 6V, VCM = 0V VCC = 2.7V, RL = 100k, VOUT = 0.25V to 2.45V VCC = 2.7V, RL = 1k, VOUT = 0.5V to 2.2V VCC = 5.0V, RL = 100k, VOUT = 0.25V to 4.75V VCC = 5.0V, RL = 1k, VOUT = 0.5V to 4.5V RL = 100k RL = 1k Operating Supply-Voltage Range Supply Current (per amplifier) VCM = VOUT = VCC / 2 VCC = 2.7V VCC = 5V Sourcing Sinking Sourcing Sinking Sourcing Sinking Sourcing Sinking VOH VOL VOH VOL 2.7 VCC - 0.20 VEE + 0.20 6.0 185 200 V A 68 84 86 84 92 76 92 86 96 80 VCC - 0.075 VEE + 0.075 V dB VCM = VEE to VCC 2 100 8 VCC + 0.15 CONDITIONS MIN TYP MAX 950 UNITS V V/C nA nA V dB dB
Large-Signal Voltage Gain (Note 1)
Output Voltage Swing (Note 1)
4
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Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
DC ELECTRICAL CHARACTERISTICS
(VCC = 2.7V to 6V, VEE = GND, VCM = 0V, VOUT = VCC / 2, TA = -55C to +125C, unless otherwise noted.) PARAMETER Input Offset Voltage Input Offset Voltage Tempco Input Bias Current Input Offset Current Common-Mode Input Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio (VEE - 0.05V) VCM (VCC + 0.05V) VCC = 2.7V to 6V VCC = 2.7V, RL = 100k, VOUT = 0.25V to 2.45V Large-Signal Voltage Gain (Note 1) VCC = 2.7V, RL = 1k, VOUT = 0.5V to 2.2V VCC = 5.0V, RL = 100k, VOUT = 0.25V to 4.75V VCC = 5.0V, RL = 1k, VOUT = 0.5V to 4.5V Output Voltage Swing (Note 1) Operating Supply-Voltage Range Supply Current (per amplifier) VCM = VOUT = VCC / 2 VCC = 2.7V VCC = 5V RL = 100k RL = 1k Sourcing Sinking Sourcing Sinking Sourcing Sinking Sourcing Sinking VOH VOL VOH VOL 2.7 VCC - 0.250 VEE + 0.250 6.0 200 225 V A VCM = VEE to VCC VCM = VEE to VCC VEE - 0.05 66 80 82 80 90 72 86 82 94 76 VCC - 0.075 VEE + 0.075 V dB VCM = VEE to VCC 2 200 10 VCC + 0.05 CONDITIONS MIN TYP MAX 1.2 UNITS mV V/C nA nA V dB dB
Note 1: RL to VEE for sourcing and VOH tests; RL to VCC for sinking and VOL tests.
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5
Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
__________________________________________Typical Operating Characteristics
(TA = +25C, VCC = 5V, VEE = 0V, unless otherwise noted.)
GAIN AND PHASE vs. FREQUENCY
80 60 GAIN PHASE (DEG) 40 GAIN (dB) 20 0 -20 PHASE 60 0 40 GAIN (dB) 20 0 -20 CL = 470pF AV = +1000 RL = 0.1
MAX492-01
GAIN AND PHASE vs. FREQUENCY
180 120 80 60 GAIN PHASE (DEG) 60 0 PHASE
MAX492-02
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
120 120 100 PSRR (dB) 80 60 40 20 VEE VCC
MAX492-03
180
140
-60 -120 -180 1000 10,000
-60 -120
AV = +1000 NO LOAD -40 0.01 0.1 1
0 -180 1000 10,000 VIN = 2.5V -20 0.1 0.01
10
100
-40 0.01
1
10
100
1
10
100
1000
FREQUENCY (kHz)
FREQUENCY (kHz)
FREQUENCY (kHz)
CHANNEL SEPARATION vs. FREQUENCY
MAX492-04
OFFSET VOLTAGE vs. TEMPERATURE
MAX492-05
COMMON-MODE REJECTION RATIO vs. TEMPERATURE
VCM = 0V TO +5V VCM = -01V TO +5.1V
MAX492-06
140 CHANNEL SEPARATION (dB) 120 100 80 60 40 20 0 0.01 VIN = 2.5V 0.1 1 10 100
160 140 OFFSET VOLTAGE (V) 120 VCM = 0V
120 110 100 CMRR (dB) 90 80 70 60 VCM = -0.2V TO +5.2V VCM = -0.3V TO +5.3V VCM = -0.4V TO +5.4V
100 80 60 40 20 0
1000 10,000
-60 -40 -20 0
20 40 60 80 100 120 140
-60 -40 -20 0
20 40 60 80 100 120 140
FREQUENCY (kHz)
TEMPERATURE (C)
TEMPERATURE (C)
INPUT BIAS CURRENT vs. COMMON-MODE VOLTAGE
MAX492-07
INPUT BIAS CURRENT vs. TEMPERATURE
MAX492-08
SUPPLY CURRENT PER AMPLIFIER vs. TEMPERATURE
SUPPLY CURRENT PER OP AMP (A) 200 180 160 140 120 100 80 60 40 20 0 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C) VCC = 5V VCC = 2.7V VOUT = VCM = VCC/2
MAX492-09
20 15 INPUT BIAS CURRENT (nA) 10 5 0 -5 -10 -15 -20 -25 -30 0 1 2 3 4 5 6 7 VCM (V) VCC = 2.7V VCC = 6V
125 100 INPUT BIAS CURRENT (nA) 75 50 25 0 -25 -50 -75 -100 -125 -60 -40 -20 0 VCC = 6V VCM = 0 VCM = VCC VCC = 2.7V VCC = 6V
220
20 40 60 80 100 120 140
TEMPERATURE (C)
6
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Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps
____________________________Typical Operating Characteristics (continued)
(TA = +25C, VCC = 5V, VEE = 0V, unless otherwise noted.)
MAX492/MAX494/MAX495
LARGE-SIGNAL GAIN vs. OUTPUT VOLTAGE
MAX492-10
LARGE-SIGNAL GAIN vs. OUTPUT VOLTAGE
MAX492-11
LARGE-SIGNAL GAIN vs. TEMPERATURE
115 LARGE-SIGNAL GAIN (dB) 110 105 100 95 90 85 80 RL TO VEE VCC = +2.7V VCC = +6V RL = 1k, 0.5V < VOUT < (VCC - 0.5V) RL TO VCC
MAX492-12 MAX492-18 MAX492-15
120 RL = 10k 110 100 GAIN (dB) 90 80 70 60 50 0 100 400 200 300 VCC - VOUT (mV) 500 VCC = +6V RL TO VEE RL = 1M
120 RL = 1M 110 100 GAIN (dB) 90 80 70 60 50 VCC = +2.7V RL TO VEE 0 100 400 200 300 VCC - VOUT (mV) 500 RL = 100k RL = 10k RL = 1k
120
RL = 100k RL = 1k
600
600
-60 -40 -20 0
20 40 60 80 100 120 140
TEMPERATURE (C)
LARGE-SIGNAL GAIN vs. OUTPUT VOLTAGE
MAX492-13
LARGE-SIGNAL GAIN vs. OUTPUT VOLTAGE
MAX492-14
LARGE-SIGNAL GAIN vs. TEMPERATURE
120 115 LARGE-SIGNAL GAIN (dB) 110 105 100 95 90 VCC = +2.7V 85 80 RL TO VEE RL = 100k, 0.3V < VOUT < (VCC - 0.3V) RL TO VCC VCC = +6V
120 110 100 GAIN (dB) 90 80 70 60 50 0 100 200 300 400 VOUT (mV) 500 VCC = +6V RL TO VCC RL = 1k RL = 10k RL = 1M RL = 100k
120 110 RL = 100k 100 GAIN (dB) 90 80 70 60 50 RL = 1k RL = 10k VCC = +2.7V RL TO VCC 0 100 200 300 400 VOUT (mV) 500 RL = 1M
600
600
-60 -40 -20 0
20 40 60 80 100 120 140
TEMPERATURE (C)
MINIMUM OUTPUT VOLTAGE vs. TEMPERATURE
MAX492-16
MAXIMUM OUTPUT VOLTAGE vs. TEMPERATURE
MAX492-17
OUTPUT IMPEDANCE vs. FREQUENCY
1000 VCM = VOUT = 2.5V OUTPUT IMPEDANCE () 100
220 200 180 160 VOUT MIN (mV) 140 120 100 80 60 40 20 0 -60 -40 -20 VCC = 2.7V, RL = 100k VCC = 6V, RL = 100k VCC = 2.7V, RL = 1k RL TO VCC VCC = 6V, RL = 1k
200 180 160 (VCC - VOUT) (mV) 140 120 100 80 60 40 20 0 VCC = 6V, RL = 100k VCC = 2.7V, RL = 100k RL TO VEE VCC = 6V, RL = 1k VCC = 2.7V, RL = 1k
10
1
0.1 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C) 0.01 0.1 1 10 100 1,000 10,000 FREQUENCY (kHz)
0 20 40 60 80 100 120 140 TEMPERATURE (C)
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Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
____________________________Typical Operating Characteristics (continued)
(TA = +25C, VCC = 5V, VEE = 0V, unless otherwise noted.)
CURRENT-NOISE DENSITY vs. FREQUENCY
MAX492-19
VOLTAGE-NOISE DENSITY vs. FREQUENCY
100 VOLTAGE-NOISE DENSITY (nV/Hz) 5.0 CURRENT-NOISE DENSITY (pA/Hz) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0.01 0.1 1 10 0.01
10
INPUT REFERRED 1 FREQUENCY (kHz)
INPUT REFERRED
0.1
1
10
FREQUENCY (kHz)
TOTAL HARMONIC DISTORTION + NOISE vs. FREQUENCY
MAX492-21
TOTAL HARMONIC DISTORTION + NOISE vs. PEAK-TO-PEAK SIGNAL AMPLITUDE
AV = +1 1kHz SINE 22kHz FILTER RL TO GND
MAX492-22
0.1 AV = +1 2VP-P SIGNAL 80kHz LOWPASS FILTER THD + NOISE (%)
0.1
THD + NOISE (%)
RL = 1k RL = 2k
0.01
0.01
RL = 10k TO GND
RL = 100k RL = 10k NO LOAD 0.001 10 100 1000 10,000 FREQUENCY (Hz) 0.001 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 PEAK-TO-PEAK SIGNAL AMPLITUDE (V)
SMALL-SIGNAL TRANSIENT RESPONSE
SMALL-SIGNAL TRANSIENT RESPONSE
MAX492-20
VIN 50mV/div
VIN 50mV/div
VOUT 50mV/div
VOUT 50mV/div
2s/div VCC = +5V, AV = +1, RL = 10k
2s/div VCC = +5V, AV = -1, RL = 10k
8
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Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps
____________________________Typical Operating Characteristics (continued)
(TA = +25C, VCC = 5V, VEE = 0V, unless otherwise noted.) LARGE-SIGNAL TRANSIENT RESPONSE LARGE-SIGNAL TRANSIENT RESPONSE
MAX492/MAX494/MAX495
VIN 2V/div
VIN 2V/div
VOUT 2V/div
VOUT 2V/div
50s/div VCC = +5V, AV = +1, RL = 10k
50s/div VCC = +5V, AV = -1, RL = 10k
______________________________________________________________Pin Description
PIN MAX492 MAX494 MAX495 1 -- -- 2 -- 3 4 5 -- 6 7 8 -- -- -- -- -- -- -- 1 -- -- 2 -- 3 11 5 -- 6 7 4 8 9 10 12 13 14 -- -- 1, 5 2 -- 3 -- 4 -- 6 -- -- 7 -- -- -- -- -- -- 8 NAME OUT1 NULL ININ1IN+ IN1+ VEE IN2+ OUT IN2OUT2 VCC OUT3 IN3IN3+ IN4+ IN4OUT4 N.C. Amplifier 1 Output Offset Null Input. Connect to a 10k potentiometer for offset-voltage trimming. Connect wiper to VEE (Figure 3). Inverting Input Amplifier 1 Inverting Input Noninverting Input Amplifier 1 Noninverting Input Negative Power-Supply Pin. Connect to ground or a negative voltage. Amplifier 2 Noninverting Input Amplifier Output Amplifier 2 Inverting Input Amplifier 2 Output Positive Power-Supply Pin. Connect to (+) terminal of power supply. Amplifier 3 Output Amplifier 3 Inverting Input Amplifier 3 Noninverting Input Amplifier 4 Noninverting Input Amplifier 4 Inverting Input Amplifier 4 Output No Connect. Not internally connected. FUNCTION
_______________________________________________________________________________________
9
Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
__________Applications Information
The dual MAX492, quad MAX494, and single MAX495 op amps combine excellent DC accuracy with rail-torail operation at both input and output. With their precision performance, wide dynamic range at low supply voltages, and very low supply current, these op amps are ideal for battery-operated equipment and other lowvoltage applications.
Input Offset Voltage
Rail-to-rail common-mode swing at the input is obtained by two complementary input stages in parallel, which feed a folded cascaded stage. The PNP stage is active for input voltages close to the negative rail, and the NPN stage is active for input voltages close to the positive rail. The offsets of the two pairs are trimmed; however, there is some small residual mismatch between them. This mismatch results in a two-level input offset characteristic, with a transition region between the levels occurring at a common-mode voltage of approximately 1.3V. Unlike other rail-to-rail op amps, the transition region has been widened to approximately 600mV in order to minimize the slight degradation in CMRR caused by this mismatch. To adjust the MAX495's input offset voltage (500V max at +25C), connect a 10k trim potentiometer between the two NULL pins (pins 1 and 5), with the wiper connected to VEE (pin 4) (Figure 2). The trim range of this circuit is 6mV. External offset adjustment is not available for the dual MAX492 or quad MAX494. The input bias currents of the MAX492/MAX494/MAX495 are typically less than 50nA. The bias current flows into the device when the NPN input stage is active, and it flows out when the PNP input stage is active. To reduce the offset error caused by input bias current flowing through external source resistances, match the effective resistance seen at each input. Connect resistor R3 between the noninverting input and ground when using
Rail-to-Rail Inputs and Outputs
The MAX492/MAX494/MAX495's input common-mode range extends 0.25V beyond the positive and negative supply rails, with excellent common-mode rejection. Beyond the specified common-mode range, the outputs are guaranteed not to undergo phase reversal or latchup. Therefore, the MAX492/MAX494/MAX495 can be used in applications with common-mode signals at or even beyond the supplies, without the problems associated with typical op amps. The MAX492/MAX494/MAX495's output voltage swings to within 50mV of the supplies with a 100k load. This rail-to-rail swing at the input and output substantially increases the dynamic range, especially in low supplyvoltage applications. Figure 1 shows the input and output waveforms for the MAX492, configured as a unity-gain noninverting buffer operating from a single +3V supply. The input signal is 3.0Vp-p, 1kHz sinusoid centered at +1.5V. The output amplitude is approximately 2.95Vp-p.
10k VIN 1 NULL
MAX495
VOUT 4 VEE NULL 5
Figure 1. Rail-to-Rail Input and Output (Voltage Follower Circuit, VCC = +3V, VEE = 0V)
10
Figure 2. Offset Null Circuit
______________________________________________________________________________________
Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps
the op amp in an inverting configuration (Figure 3a); connect resistor R3 between the noninverting input and the input signal when using the op amp in a noninverting configuration (Figure 3b). Select R3 to equal the parallel combination of R1 and R2. High source resistances will degrade noise performance, due to the thermal noise of the resistor and the input current noise (which is multiplied by the source resistance). (Figure 4). The diodes limit the differential voltage applied to the amplifiers' internal circuitry to no more than VF, where VF is the diodes' forward-voltage drop (about 0.7V at +25C). Input bias current for the ICs (25nA typical) is specified for the small differential input voltages. For large differential input voltages (exceeding VF), this protection circuitry increases the input current at IN+ and IN-: (VIN+ - VIN- ) - VF Input Current = ---------------------- 2 x 1.7k For comparator applications requiring large differential voltages (greater than VF), you can limit the input current that flows through the diodes with external resistors
MAX492/MAX494/MAX495
Input Stage Protection Circuitry The MAX492/MAX494/MAX495 include internal protection circuitry that prevents damage to the precision input stage from large differential input voltages. This protection circuitry consists of back-to-back diodes between IN+ and IN- with two 1.7k resistors in series
R2 IN+ R1 VIN
1.7k
TO INTERNAL CIRCUITRY
MAX492 MAX494 MAX495
MAX49_
VOUT
R3
R3 = R2 II R1 IN- 1.7k TO INTERNAL CIRCUITRY
Figure 3a. Reducing Offset Error Due to Bias Current: Inverting Configuration
Figure 4. Input Stage Protection Circuitry
R3 CAPACITIVE LOAD (pF) VIN UNSTABLE REGION
MAX49_
R2 R3 = R2 II R1 R1
VOUT
1000
VCC = +5V VOUT = VCC/2 RL TO VEE AV = +1 100 1 10 RESISTIVE LOAD (k) 100
Figure 3b. Reducing Offset Error Due to Bias Current: Figure 5. Capacitive-Load Stable Region Sourcing Current Noninverting Configuration ______________________________________________________________________________________ 11
MAX492-FG 04
10,000
Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
in series with IN-, IN+, or both. Series resistors are not recommended for amplifier applications, as they may increase input offsets and decrease amplifier bandwidth. In op amp circuits, driving large capacitive loads increases the likelihood of oscillation. This is especially true for circuits with high loop gains, such as a unitygain voltage follower. The output impedance and a capacitive load form an RC network that adds a pole to the loop response and induces phase lag. If the pole frequency is low enough--as when driving a large capacitive load--the circuit phase margin is degraded, leading to either an under-damped pulse response or oscillation.
Output Loading and Stability
Even with their low quiescent current of less than 150A per op amp, the MAX492/MAX494/MAX495 are well suited for driving loads up to 1k while maintaining DC accuracy. Stability while driving heavy capacitive loads is another key advantage over comparable CMOS railto-rail op amps.
VIN 50mV/div
VIN 50mV/div
VOUT 50mV/div
VOUT 50mV/div
10s/div
10s/div
Figure 6. MAX492 Voltage Follower with 1000pF Load (RL = )
Figure 7b. MAX492 Voltage Follower with 500pF Load-- RL = 20k
VIN 50mV/div
VIN 50mV/div
VOUT 50mV/div
VOUT 50mV/div
10s/div
10s/div
Figure 7a. MAX492 Voltage Follower with 500pF Load-- RL = 5k
12
Figure 7c. MAX492 Voltage Follower with 500pF Load-- RL =
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Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps
The MAX492/MAX494/MAX495 can drive capacitive loads in excess of 1000pF under certain conditions (Figure 5). When driving capacitive loads, the greatest potential for instability occurs when the op amp is sourcing approximately 100A. Even in this case, stability is maintained with up to 400pF of output capacitance. If the output sources either more or less current, stability is increased. These devices perform well with a 1000pF pure capacitive load (Figure 6). Figure 7 shows the performance with a 500pF load in parallel with various load resistors. To increase stability while driving large capacitive loads, connect a pull-up resistor at the output to decrease the current that the amplifier must source. If the amplifier is made to sink current rather than source, stability is further increased. Frequency stability can be improved by adding an output isolation resistor (RS) to the voltage-follower circuit (Figure 8). This resistor improves the phase margin of the circuit by isolating the load capacitor from the op amp's output. Figure 9a shows the MAX492 driving 10,000pF (RL 100k), while Figure 9b adds a 47 isolation resistor.
MAX492/MAX494/MAX495
VIN 50mV/div RS
MAX49_
VIN
VOUT CL VOUT 50mV/div
10s/div
Figure 8. Capacitive-Load Driving Circuit
Figure 9b. Driving a 10,000pF Capacitive Load with a 47 Isolation Resistor
+5V VIN 50mV/div 2 1k
VCC
7 6
MAX495
3 VOUT 50mV/div 1k 4
VOUT
10s/div
Figure 9a. Driving a 10,000pF Capacitive Load
Figure 10. Power-Up Test Configuration
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13
Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
VCC 1V/div
VCC 2V/div
VOUT 500mV/div
VOUT 1V/div
5s/div
5s/div
Figure 11a. Power-Up Settling Time (VCC = +3V)
Figure 11b. Power-Up Settling Time (VCC = +5V)
Because the MAX492/MAX494/MAX495 have excellent stability, no isolation resistor is required, except in the most demanding applications. This is beneficial because an isolation resistor would degrade the lowfrequency performance of the circuit.
Power Supplies and Layout
The MAX492/MAX494/MAX495 operate from a single 2.7V to 6V power supply, or from dual supplies of 1.35V to 3V. For single-supply operation, bypass the power supply with a 1F capacitor in parallel with a 0.1F ceramic capacitor. If operating from dual supplies, bypass each supply to ground. Good layout improves performance by decreasing the amount of stray capacitance at the op amp's inputs and output. To decrease stray capacitance, minimize both trace lengths and resistor leads and place external components close to the op amp's pins.
Power-Up Settling Time
The MAX492/MAX494/MAX495 have a typical supply current of 150A per op amp. Although supply current is already low, it is sometimes desirable to reduce it further by powering down the op amp and associated ICs for periods of time. For example, when using a MAX494 to buffer the inputs to a multi-channel analog-to-digital converter (ADC), much of the circuitry could be powered down between data samples to increase battery life. If samples are taken infrequently, the op amps, along with the ADC, may be powered down most of the time. When power is reapplied to the MAX492/MAX494/ MAX495, it takes some time for the voltages on the supply pin and the output pin of the op amp to settle. Supply settling time depends on the supply voltage, the value of the bypass capacitor, the output impedance of the incoming supply, and any lead resistance or inductance between components. Op amp settling time depends primarily on the output voltage and is slew-rate limited. With the noninverting input to a voltage follower held at mid-supply (Figure 10), when the supply steps from 0V to VCC, the output settles in approximately 4s for V CC = +3V (Figure 11a) or 10s for V CC = +5V (Figure 11b).
Rail-to-Rail Buffers
The Typical Operating Circuit shows a MAX495 gain-oftwo buffer driving the analog input to a MAX187 12-bit ADC. Both devices run from a single 5V supply, and the converter's internal reference is 4.096V. The MAX495's typical input offset voltage is 200V. This results in an error at the ADC input of 400V, or less than half of one least significant bit (LSB). Without offset trimming, the op amp contributes negligible error to the conversion result.
14
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Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps
_Ordering Information (continued)
PART MAX494CPD MAX494CSD MAX494EPD MAX494ESD MAX494MJD MAX495CPA MAX495CSA MAX495CUA MAX495C/D MAX495EPA MAX495ESA MAX495MJA TEMP. RANGE 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 14 Plastic DIP 14 SO 14 Plastic DIP 14 SO 14 CERDIP 8 Plastic DIP 8 SO 8 MAX Dice* 8 Plastic DIP 8 SO 8 CERDIP
IN1+ V CC
_________________Chip Topographies
MAX492
IN1OUT1
MAX492/MAX494/MAX495
0.068" (1.728mm) V EE V CC
V CC IN2+ IN2-
OUT2
* Dice are specified at TA = +25C, DC parameters only.
0.069" (1.752mm)
____Pin Configurations (continued)
TOP VIEW
INOUT1 1 IN1- 2 IN1+ 3 VCC 4 IN2+ 5 IN2- 6 OUT2 7 14 OUT4 13 IN412 IN4+
MAX495
NULL1
V CC
0.056" (1.422mm) IN+ OUT
MAX494
11 VEE 10 IN3+ 9 8 IN3OUT3
V EE
NULL2
DIP/SO
0.055" (1.397mm)
TRANSISTOR COUNT: 134 (single MAX495) 268 (dual MAX492) 536 (quad MAX494) SUBSTRATE CONNECTED TO VEE
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15
Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps MAX492/MAX494/MAX495
________________________________________________________Package Information
DIM
C A 0.101mm 0.004 in B A1 L
e
A A1 B C D E e H L
INCHES MAX MIN 0.044 0.036 0.008 0.004 0.014 0.010 0.007 0.005 0.120 0.116 0.120 0.116 0.0256 0.198 0.188 0.026 0.016 6 0
MILLIMETERS MIN MAX 0.91 1.11 0.10 0.20 0.25 0.36 0.13 0.18 2.95 3.05 2.95 3.05 0.65 4.78 5.03 0.41 0.66 0 6
21-0036D
E
H
8-PIN MAX MICROMAX SMALL-OUTLINE PACKAGE
D
DIM
D A e B
0.101mm 0.004in.
0-8
A1
C
L
A A1 B C E e H L
INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.157 0.150 0.050 0.244 0.228 0.050 0.016
MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 3.80 4.00 1.27 5.80 6.20 0.40 1.27
E
H
Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.)
DIM PINS D D D 8 14 16
INCHES MILLIMETERS MIN MAX MIN MAX 0.189 0.197 4.80 5.00 0.337 0.344 8.55 8.75 0.386 0.394 9.80 10.00
21-0041A
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) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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