Not Recommended for New Designs


The MAX495 was manufactured for Maxim by an outside wafer foundry using a process that is no longer available. It is not recommended for new designs. A Maxim replacement or an industry second-source may be available. The data sheet remains available for existing users. The other parts on the following data sheet are not affected.

For further information, please see the QuickView data sheet for this part or contact technical support for assistance.

19-0265; Rev 2; 9/96


Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op Amps

MAX492/MAX494/MAX495

General Description Features

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 150µA 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 appli-

cations. The MAX492/MAX494/MAX495 are available in Ordering Information

DIP and SO packages in the industry-standard op-amp

PART

TEMP. RANGE

PIN-PACKAGE

MAX492CPA

0°C to

+70°C

8 Plastic DIP

MAX492CSA

0°C to

+70°C

8 SO

MAX492C/D

0°C to

+70°C

Dice*

MAX492EPA

-40°C to

+85°C

8 Plastic DIP

MAX492ESA

-40°C to

+85°C

8 SO

MAX492MJA

-55°C to

+125°C

8 CERDIP

pin configurations. The MAX495 is also available in the smallest 8-pin SO: the µMAX package.


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 = +25°C, DC parameters only.


Typical Operating Circuit Pin Configurations



+5V

1

VDD

10k

MAX187

2 7 (ADC) 6

DOUT

6 2 AIN SCLK 8 SERIAL

MAX495 7 INTERFACE

ANALOG 3 CS

INPUT 4

SHDN 3

10k REF 4 4.096V

GND 5


INPUT SIGNAL CONDITIONING FOR LOW-VOLTAGE ADC

TOPVIEW


OUT1 1 8 VCC

IN1- 2 7 OUT2

IN1+ 3 6 IN2-

VEE 4 5 IN2+

MAX492

DIP/SO


NULL 1 8 N.C.

IN1- 2 MAX495 7 VCC

IN1+ 3 6 OUT

VEE 4 5 NULL


DIP/SO/MAX

PinConfigurations continuedatendof datasheet.

Maxim Integrated Products 1

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800


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 = +70°C)

8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ....727mW 8-Pin SO (derate 5.88mW/°C above +70°C).................471mW

8-Pin CERDIP (derate 8.00mW/°C above +70°C).........640mW

8-Pin µMAX (derate 4.1mW/°C above +70°C) ..............330mW


14-Pin Plastic DIP (derate 10.00mW/°C above +70°C)...800mW 14-Pin SO (derate 8.33mW/°C above +70°C)...............667mW

14-Pin CERDIP (derate 9.09mW/°C above +70°C).......727mW Operating Temperature Ranges

MAX49_C_ _ ........................................................0°C to +70°C

MAX49_E_ _......................................................-40°C to +85°C

MAX49_M_ _ ...................................................-55°C to +125°C

Junction Temperatures

MAX49_C_ _/E_ _..........................................................+150°C

MAX49_M_ _ .................................................................+175°C

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

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

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 = +25°C, unless otherwise noted.)


PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Input Offset Voltage

VCM = VEE to VCC

±200 ±500

µV

Input Bias Current

VCM = VEE to VCC

±25 ±60

nA

Input Offset Current

VCM = VEE to VCC

±0.5 ±6

nA

Differential Input Resistance


2

M

Common-Mode Input

Voltage Range


VEE - 0.25


VCC + 0.25

V

Common-Mode Rejection Ratio

(VEE - 0.25V) VCM (VCC + 0.25V)

74

90


dB

Power-Supply Rejection Ratio

VCC = 2.7V to 6V

88

110


dB


Large-Signal Voltage Gain (Note 1)

VCC = 2.7V, RL = 100k,

VOUT = 0.25V to 2.45V

Sourcing

90

104



dB

Sinking

90

102


VCC = 2.7V, RL = 1k, VOUT = 0.5V to 2.2V

Sourcing

94

105


Sinking

78

90


VCC = 5.0V, RL = 100k,

VOUT = 0.25V to 4.75V

Sourcing

98

108


Sinking

92

100


VCC = 5.0V, RL = 1k, VOUT = 0.5V to 4.5V

Sourcing

98

110


Sinking

86

98



Output Voltage Swing (Note 1)

RL = 100k

VOH

VCC - 0.075 VCC - 0.04


V

VOL

VEE + 0.04 VEE + 0.075

RL = 1k

VOH

VCC - 0.20

VCC - 0.15


VOL

VEE + 0.15 VEE + 0.20

Output Short-Circuit Current


30

mA

Operating Supply Voltage Range


2.7


6.0

V

Supply Current (per amplifier)

VCM = VOUT = VCC / 2

VCC = 2.7V

135 150

µA

VCC = 5V

150 170


MAX492/MAX494/MAX495

AC ELECTRICAL CHARACTERISTICS

(VCC = 2.7V to 6V, VEE = GND, TA = +25°C, unless otherwise noted.)


PARAMETER

CONDITIONS

MIN TYP MAX

UNITS

Gain-Bandwidth Product

RL = 100k, CL = 100pF

500

kHz

Phase Margin

RL = 100k, CL = 100pF

60

degrees

Gain Margin

RL = 100k, CL = 100pF

10

dB

Total Harmonic Distortion

RL = 10k, CL = 15pF, VOUT = 2Vp-p, AV = +1, f = 1kHz

0.003

%

Slew Rate

RL = 100k, CL = 15pF

0.20

V/µs

Time

To 0.1%, 2V step

12

µs

Turn-On Time

VCC = 0V to 3V step, VIN = VCC / 2, AV = +1

5

µs

Input Noise-Voltage Density

f = 1kHz

25

nV/Hz

Input Noise-Current Density

f = 1kHz

0.1

pA/Hz

Amp-Amp Isolation

f = 1kHz

125

dB


DC ELECTRICAL CHARACTERISTICS

(VCC = 2.7V to 6V, VEE = GND, VCM = 0V, VOUT = VCC / 2, TA = 0°C to +70°C, unless otherwise noted.)


PARAMETER

CONDITIONS

MIN TYP MAX

UNITS

Input Offset Voltage

VCM = VEE to VCC

±650

µV

Input Offset Voltage Tempco


±2

µV/°C

Input Bias Current

VCM = VEE to VCC

±75

nA

Input Offset Current

VCM = VEE to VCC

±6

nA

Common-Mode Input

Voltage Range


VEE - 0.20 VCC + 0.20

V

Common-Mode Rejection Ratio

(VEE - 0.20) VCM (VCC + 0.20)

72

dB

Power-Supply Rejection Ratio

VCC = 2.7V to 6V

86

dB


Large-Signal Voltage Gain (Note 1)

VCC = 2.7V, RL = 100k, VOUT = 0.25V to 2.45V

Sourcing

88


dB

Sinking

84

VCC = 2.7V, RL = 1k, VOUT = 0.5V to 2.2V

Sourcing

92

Sinking

76

VCC = 5.0V, RL = 100k, VOUT = 0.25V to 4.75V

Sourcing

92

Sinking

88

VCC = 5.0V, RL = 1k, VOUT = 0.5V to 4.5V

Sourcing

96

Sinking

82


Output Voltage Swing (Note 1)

RL = 100k

VOH

VCC - 0.075


V

VOL

VEE + 0.075

RL = 1k

VOH

VCC - 0.20

VOL

VEE + 0.20

Operating Supply Voltage Range


2.7 6.0

V

Supply Current (per amplifier)

VCM = VOUT = VCC / 2

VCC = 2.7V

175

µA

VCC = 5V

190


MAX492/MAX494/MAX495

DC ELECTRICAL CHARACTERISTICS

(VCC = 2.7V to 6V, VEE = GND, VCM = 0V, VOUT = VCC / 2, TA = -40°C to +85°C, unless otherwise noted.)


PARAMETER

CONDITIONS

MIN TYP MAX

UNITS

Input Offset Voltage

VCM = VEE to VCC

±950

µV

Input Offset Voltage Tempco


±2

µV/°C

Input Bias Current

VCM = VEE to VCC

±100

nA

Input Offset Current

VCM = VEE to VCC

±8

nA

Common-Mode Input

Voltage Range


VEE - 0.15 VCC + 0.15

V

Common-Mode Rejection Ratio

(VEE - 0.15) VCM (VCC + 0.15)

68

dB

Power-Supply Rejection Ratio

VCC = 2.7V to 6V, VCM = 0V

84

dB


Large-Signal Voltage Gain (Note 1)

VCC = 2.7V, RL = 100k, VOUT = 0.25V to 2.45V

Sourcing

86


dB

Sinking

84

VCC = 2.7V, RL = 1k, VOUT = 0.5V to 2.2V

Sourcing

92

Sinking

76

VCC = 5.0V, RL = 100k, VOUT = 0.25V to 4.75V

Sourcing

92

Sinking

86

VCC = 5.0V, RL = 1k, VOUT = 0.5V to 4.5V

Sourcing

96

Sinking

80


Output Voltage Swing (Note 1)

RL = 100k

VOH

VCC - 0.075


V

VOL

VEE + 0.075

RL = 1k

VOH

VCC - 0.20

VOL

VEE + 0.20

Operating Supply-Voltage Range


2.7 6.0

V

Supply Current (per amplifier)

VCM = VOUT = VCC / 2

VCC = 2.7V

185

µA

VCC = 5V

200


MAX492/MAX494/MAX495

DC ELECTRICAL CHARACTERISTICS

(VCC = 2.7V to 6V, VEE = GND, VCM = 0V, VOUT = VCC / 2, TA = -55°C to +125°C, unless otherwise noted.)


PARAMETER

CONDITIONS

MIN TYP MAX

UNITS

Input Offset Voltage

VCM = VEE to VCC

±1.2

mV

Input Offset Voltage Tempco


±2

µV/°C

Input Bias Current

VCM = VEE to VCC

±200

nA

Input Offset Current

VCM = VEE to VCC

±10

nA

Common-Mode Input Voltage Range


VEE - 0.05 VCC + 0.05

V

Common-Mode Rejection Ratio

(VEE - 0.05V) VCM (VCC + 0.05V)

66

dB

Power-Supply Rejection Ratio

VCC = 2.7V to 6V

80

dB


Large-Signal Voltage Gain (Note 1)

VCC = 2.7V, RL = 100k, VOUT = 0.25V to 2.45V

Sourcing

82


dB

Sinking

80

VCC = 2.7V, RL = 1k, VOUT = 0.5V to 2.2V

Sourcing

90

Sinking

72

VCC = 5.0V, RL = 100k, VOUT = 0.25V to 4.75V

Sourcing

86

Sinking

82

VCC = 5.0V, RL = 1k, VOUT = 0.5V to 4.5V

Sourcing

94

Sinking

76


Output Voltage Swing (Note 1)

RL = 100k

VOH

VCC - 0.075


V

VOL

VEE + 0.075

RL = 1k

VOH

VCC - 0.250

VOL

VEE + 0.250

Operating Supply-Voltage Range


2.7 6.0

V

Supply Current (per amplifier)

VCM = VOUT = VCC / 2

VCC = 2.7V

200

µA

VCC = 5V

225

Note 1: RL to VEE for sourcing and VOH tests; RL to VCC for sinking and VOL tests.


MAX492/MAX494/MAX495

Typical Operating Characteristics

(TA = +25°C, VCC = 5V, VEE = 0V, unless otherwise noted.)



80


60


GAIN (dB)

40


20


0


-20


-40

GAINAND PHASE vs. FREQUENCY



H


P

GAIN


ASE


AV = +1000 NO LOAD


MAX492-01 180


120


PHASE (DEG)

60


0


-60


-120


-180


80


60


GAIN (dB)

40


20


0


-20


-40

GAINAND PHASE vs. FREQUENCY


GA

IN


P

HASE


CL = 470pF AV = +1000 RL =


MAX492-02 180


120


PHASE (DEG)

60


0


-60


-120


-180


140

120


100

PSRR (dB)

80


60


40


20


0


-20

POWER-SUPPLY REJECTIONRATIO vs. FREQUENCY




V


CC


MAX492-03

VEE


VIN = 2.5V

0.01

0.1 1

10 100 1000 10,000

0.01

0.1 1

10 100 1000 10,000

0.01

0.1 1

10 100

1000

FREQUENCY (kHz)

FREQUENCY (kHz)

FREQUENCY (kHz)



140


CHANNEL SEPARATION (dB)

120


100


80


60


40


20


0

CHANNELSEPARATION vs. FREQUENCY


VIN = 2.5V


160


MAX492-04

140


OFFSET VOLTAGE (V)

120


100


80


60


40


20


0

OFFSET VOLTAGE vs. TEMPERATURE


MAX492-05

120


110


CMRR (dB)

100


90


80


70


60

COMMON-MODEREJECTIONRATIO vs. TEMPERATURE


MAX492-06

VCM = 0V TO+5V VCM = -01V TO+5.1V


VCM = -0.2V TO+5.2V VCM = -0.3V TO+5.3V VCM = -0.4V TO+5.4V







VCM = 0V







































































0.01

0.1 1

10 100 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 BIASCURRENT vs. COMMON-MODE VOLTAGE

20


MAX492-07

125

INPUT BIASCURRENT vs. TEMPERATURE


MAX492-08

220

SUPPLY CURRENT PERAMPLIFIER vs. TEMPERATURE

15

INPUT BIAS CURRENT (nA)

10

5

0

-5

-10

-15

-20

-25

-30


VCC= 6V

VCC


= 2.7V

100

INPUT BIAS CURRENT (nA)

75

50

25

0

-25

-50

-75

-100

-125


MAX492-09

VCM = VCC


VCM = 0


VCC= 6V


VCC= 2.7V


VCC= 6V

200

SUPPLY CURRENT PEROP AMP (A)

180

160

140

120

100

80

60

40

20

0

VOUT = VCM = VCC/2


VCC= 5V


VCC= 2.7V

0 1 2 3

4 5 6 7

-60 -40 -20 0

20 40 60

80 100 120 140

-60 -40 -20 0

20 40 60

80 100 120 140

VCM (V)

TEMPERATURE (C)

TEMPERATURE (C)


MAX492/MAX494/MAX495

Typical Operating Characteristics (continued)

(TA = +25°C, VCC = 5V, VEE = 0V, unless otherwise noted.)



120


110


GAIN (dB)

100


90


80


70


60


50


LARGE-SIGNALGAIN vs. OUTPUT VOLTAGE


RL = 10k

RL = 1M RL = 100k

RL = 1k



V

VCC= +6 RL TOVEE


120


MAX492-10

110


GAIN (dB)

100


90


80


70


60


50


LARGE-SIGNALGAIN vs. OUTPUT VOLTAGE


RL = 1M


RL = 100k RL = 10k

RL = 1k


VCC= +2.7V RL TOVEE


120


MAX492-11

LARGE-SIGNAL GAIN (dB)

115


110


105


100


95


90


85


80


LARGE-SIGNALGAIN vs. TEMPERATURE


MAX492-12

RL = 1k, 0.5V < VOUT < (VCC- 0.5V) RL TOVCC


VCC= +2.7V

VCC= +6V

RL TOVEE

0 100

200

300 400

500

600

0 100

200

300 400

500

600

-60 -40 -20 0 20

40 60 80 100 120 140

VCC- VOUT (mV)

VCC- VOUT (mV)

TEMPERATURE (C)



120


110


GAIN (dB)

100


90


80


70

LARGE-SIGNALGAIN vs. OUTPUT VOLTAGE


RL = 1M RL = 100k


RL = 1k RL = 10k


120


MAX492-13

110


GAIN (dB)

100


90


80


70

LARGE-SIGNALGAIN vs. OUTPUT VOLTAGE


RL = 1M

RL = 100k


RL = 1k RL = 10k


120


MAX492-14

LARGE-SIGNAL GAIN (dB)

115


110


105


100


95


90

LARGE-SIGNALGAIN vs. TEMPERATURE

MAX492-15

RL = 100k, 0.3V < VOUT < (VCC- 0.3V) RL TOVCC

VCC= +6V


RL TOVEE

60 VCC= +6V 60

RL TOVCC

50 50

VCC= +2.7V 85

RL TOVCC

80

VCC= +2.7V

0 100

200 300 400

500

600

0 100

200 300 400

500

600

-60 -40 -20 0 20

40 60 80 100 120 140

VOUT (mV)

VOUT (mV)

TEMPERATURE (C)

220

200

MINIMUM OUTPUT VOLTAGE vs. TEMPERATURE

RL TOVCC

200

MAX492-16

180

MAXIMUM OUTPUT VOLTAGE vs. TEMPERATURE

RL TOVEE

1000

OUTPUT IMPEDANCE vs. FREQUENCY

VCM = VOUT = 2.5

MAX492-18

V

180

VOUT MIN (mV)

160

140

120

100

80

VCC= 6V, RL = 1k


VCC= 2.7V, RL = 1k

160

(VCC- VOUT) (mV)

140

120

100

80


VCC

= 6V, RL = 1k


VCC= 2.7V, RL = 1k


MAX492-17

100


OUTPUT IMPEDANCE ( )

10

60 VCC

40

20

0

= 6V, RL = 100k


VCC= 2.7V, RL = 100k

60 VCC= 6V, RL = 100k

40 VCC= 2.7V, RL = 100k

20

0


1


0.1

-60 -40 -20 0

20 40 60 80 100 120140

-60 -40 -20 0

20 40 60 80 100 120140

0.01

0.1 1

10 100 1,000 10,000

TEMPERATURE (C)

TEMPERATURE (C)

FREQUENCY (kHz)


MAX492/MAX494/MAX495

Typical Operating Characteristics (continued)

MAX492-19

(TA = +25°C, VCC = 5V, VEE = 0V, unless otherwise noted.)



VOLTAGE-NOISE DENSITY (nV/Hz)

100


10


1

VOLTAGE-NOISEDENSITY vs. FREQUENCY


INPUT REFERRED


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

CURRENT-NOISEDENSITY vs. FREQUENCY





























































































































INPUT RE

FE

RRED
























MAX492-20

0.01

0.1

1 10

0.01

0.1

1 10

FREQUENCY (kHz)

FREQUENCY (kHz)



0.1


THD + NOISE (%)

0.01


0.001


TOTALHARMONICDISTORTION + NOISE vs. FREQUENCY


AV

=

+1


2V

R

E

LT

FI

PASS

LO

z

kH

80

L

NA

IG

S

P-P

MAX492-21

W


RL = 10k TOGND


NO LOAD


0.1


THD + NOISE (%)

0.01


0.001

TOTALHARMONICDISTORTION + NOISE vs. PEAK-TO-PEAKSIGNALAMPLITUDE


MAX492-22

AV = +1 1kHz SINE

22kHz FILTER

RL TOGND RL = 1k

RL = 2k


RL = 100k

RL = 10k

10 100

1000

10,000

4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0

FREQUENCY (Hz)

PEAK-TO-PEAK SIGNAL AMPLITUDE (V)


SMALL-SIGNAL TRANSIENT RESPONSE SMALL-SIGNAL TRANSIENT RESPONSE


VIN

50mV/div


VOUT

50mV/div

VIN

50mV/div


VOUT

50mV/div


2s/div VCC=+5V,AV=+1,RL=10k

2s/div VCC=+5V,AV= -1,RL=10k


MAX492/MAX494/MAX495

Typical Operating Characteristics (continued)

(TA = +25°C, VCC = 5V, VEE = 0V, unless otherwise noted.)


LARGE-SIGNAL TRANSIENT RESPONSE LARGE-SIGNAL TRANSIENT RESPONSE


VIN

2V/div


VOUT

2V/div

VIN

2V/div


VOUT

2V/div


50s/div VCC=+5V,AV=+1,RL=10k

50s/div VCC=+5V,AV= -1,RL=10k



Pin Description


PIN

NAME

FUNCTION

MAX492

MAX494

MAX495

1

1

OUT1

Amplifier 1 Output

1, 5

NULL

Offset Null Input. Connect to a 10k potentiometer for offset-voltage trimming. Connect wiper to VEE (Figure 3).

2

IN-

Inverting Input

2

2

IN1-

Amplifier 1 Inverting Input

3

IN+

Noninverting Input

3

3

IN1+

Amplifier 1 Noninverting Input

4

11

4

VEE

Negative Power-Supply Pin. Connect to ground or a negative voltage.

5

5

IN2+

Amplifier 2 Noninverting Input

6

OUT

Amplifier Output

6

6

IN2-

Amplifier 2 Inverting Input

7

7

OUT2

Amplifier 2 Output

8

4

7

VCC

Positive Power-Supply Pin. Connect to (+) terminal of power supply.

8

OUT3

Amplifier 3 Output

9

IN3-

Amplifier 3 Inverting Input

10

IN3+

Amplifier 3 Noninverting Input

12

IN4+

Amplifier 4 Noninverting Input

13

IN4-

Amplifier 4 Inverting Input

14

OUT4

Amplifier 4 Output

8

N.C.

No Connect. Not internally connected.


MAX492/MAX494/MAX495

Applications Information

The dual MAX492, quad MAX494, and single MAX495 op amps combine excellent DC accuracy with rail-to- rail operation at both input and output. With their preci- sion performance, wide dynamic range at low supply voltages, and very low supply current, these op amps are ideal for battery-operated equipment and other low- voltage applications.

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 out- puts 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 supply- voltage applications. Figure 1 shows the input and out- put 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 approxi- mately 2.95Vp-p.

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 posi- tive 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 characteris- tic, 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 (500µV max at +25°C), connect a 10k trim potentiometer between the two NULL pins (pins 1 and 5), with the wiper con- nected to VEE (pin 4) (Figure 2). The trim range of this circuit is ±6mV. External offset adjustment is not avail- able 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 effec- tive resistance seen at each input. Connect resistor R3 between the noninverting input and ground when using



VIN


VOUT


10k

1 NULL


MAX495


4 5

VEE NULL

Figure 1. Rail-to-Rail Input and Output (Voltage Follower Circuit, VCC = +3V, VEE = 0V)

Figure 2. Offset Null Circuit


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 noninvert- ing configuration (Figure 3b). Select R3 to equal the parallel combination of R1 and R2. High source resis- tances will degrade noise performance, due to the ther- mal noise of the resistor and the input current noise (which is multiplied by the source resistance).

Input Stage Protection Circuitry The MAX492/MAX494/MAX495 include internal protec- tion 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


R1

VIN

VOUT

MAX49_


R3 R3=R2 IIR1

Figure 3a. Reducing Offset Error Due to Bias Current: Inverting Configuration



R3

VIN

VOUT

MAX49_

R2

R3=R2 IIR1


R1

Figure 3b. Reducing Offset Error Due to Bias Current: Noninverting Configuration

(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 +25°C).

MAX492/MAX494/MAX495

Input bias current for the ICs (±25nA typical) is speci- fied for the small differential input voltages. For large differential input voltages (exceeding VF), this protec- tion 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 cur- rent that flows through the diodes with external resistors



MAX492 MAX494

1.7k TOINTERNAL MAX495

IN+ CIRCUITRY


IN– TOINTERNAL

1.7k CIRCUITRY

1000

CAPACITIVE LOAD (pF)

MAX492-FG 04

Figure 4. Input Stage Protection Circuitry


10,000

UNSTABLE REGION


100


1

10

RESISTIVE LOAD (k)

100


VCC= +5V VOUT = VCC/2 RL TOVEE AV = +1

Figure 5. Capacitive-Load Stable Region Sourcing Current


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.

Output Loading and Stability Even with their low quiescent current of less than 150µA 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 rail- to-rail op amps.



VIN

50mV/div


VOUT

50mV/div


10s/div

Figure 6. MAX492 Voltage Follower with 1000pF Load (RL = )

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 unity- gain 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.




VIN

50mV/div


VOUT

50mV/div


10s/div

Figure 7b. MAX492 Voltage Follower with 500pF Load— RL = 20k




VIN

50mV/div


VOUT

50mV/div


10s/div


VIN

50mV/div


VOUT

50mV/div


10s/div


Figure 7a. MAX492 Voltage Follower with 500pF Load— RL = 5k

Figure 7c. MAX492 Voltage Follower with 500pF Load— RL =


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 100µA. Even in this case, sta- bility is maintained with up to 400pF of output capaci- tance. 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 vari- ous load resistors.



RS

MAX49_ VOUT

CL

VIN

Figure 8. Capacitive-Load Driving Circuit




VIN

50mV/div


VOUT

50mV/div


10s/div

Figure 9a. Driving a 10,000pF Capacitive Load

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.

MAX492/MAX494/MAX495

Frequency stability can be improved by adding an out- put 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.



VIN

50mV/div


VOUT

50mV/div


10s/div

Figure 9b. Driving a 10,000pF Capacitive Load with a 47 Isolation Resistor




+5V VCC


2

1k 7

6 VOUT

MAX495

3 4


1k

Figure 10. Power-Up Test Configuration



VCC

1V/div


VOUT

500mV/div


5s/div


VCC

2V/div


VOUT

1V/div


5s/div

MAX492/MAX494/MAX495

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 low- frequency performance of the circuit.

Power-Up Settling Time The MAX492/MAX494/MAX495 have a typical supply current of 150µA 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 con- verter (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 sup- ply 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 induc- tance 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 4µs for VCC = +3V (Figure 11a) or 10µs for VCC = +5V (Figure 11b).

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 1µF capacitor in parallel with a 0.1µF ceramic capacitor. If operating from dual sup- plies, 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.

Rail-to-Rail Buffers The Typical Operating Circuit shows a MAX495 gain-of- two 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 200µV. This results in an error at the ADC input of 400µV, or less than half of one least significant bit (LSB). Without offset trimming, the op amp contributes negligible error to the conversion result.


MAX492/MAX494/MAX495

_Ordering Information (continued) Chip Topographies

PART

TEMP. RANGE

PIN-PACKAGE

MAX494CPD

0°C to

+70°C

14 Plastic DIP

MAX494CSD

0°C to

+70°C

14 SO

MAX494EPD

-40°C to

+85°C

14 Plastic DIP

MAX494ESD

-40°C to

+85°C

14 SO

MAX494MJD

-55°C to

+125°C

14 CERDIP

MAX495CPA

0°C to

+70°C

8 Plastic DIP

MAX495CSA

0°C to

+70°C

8 SO

MAX495CUA

0°C to

+70°C

8 µMAX

MAX495C/D

0°C to

+70°C

Dice*

MAX495EPA

-40°C to

+85°C

8 Plastic DIP

MAX495ESA

-40°C to

+85°C

8 SO

MAX495MJA

-55°C to

+125°C

8 CERDIP

MAX492


IN1+ IN1-


VCC


VEE


OUT1


0.068"

(1. 728mm) VCC



* Dice are specified at TA = +25°C, DC parameters only.

VCC


IN2+


IN2-

OUT2

0.069"

(1. 752mm)


Pin Configurations (continued)


IN-


IN+


NULL1


VEE


MAX495


NULL2


VCC


0.056"

(1. 422mm) OUT


TOPVIEW


OUT1 1 14 OUT4

IN1- 2 13 IN4-

IN1+ 3 12 IN4+

VCC 4 MAX494 11 VEE

IN2+ 5 10 IN3+

IN2- 6 9 IN3-

OUT2 7 8 OUT3


DIP/SO

0.055"

(1. 397mm)


TRANSISTOR COUNT: 134 (single MAX495)

268 (dual MAX492)

536 (quad MAX494) SUBSTRATE CONNECTED TO VEE


MAX492/MAX494/MAX495

Package Information











DIM

INCHES

MILLIMETERS










MIN

MAX

MIN

MAX









C


A

0.036

0.044

0.91

1.11

A1

0.004

0.008

0.10

0.20

B

0.010

0.014

0.25

0.36






A












0.101mm


C

0.005

0.007

0.13

0.18

D

0.116

0.120

2.95

3.05

e





0.004 in


E

0.116

0.120

2.95

3.05




B


A1



L

e

0.0

256

0.

65










H

0.188

0.198

4.78

5.03










L

0.016

0.026

0.41

0.66













D



E



H



8-PIN MAX MICROMAX SMALL-OUTLINE

PACKAGE




21-0036D



e


D


B


A1


A



0.101mm

0.004in.


0°-8°


C L

DIM

INCHES

MILLIMETERS

MIN

MAX

MIN

MAX

A

0.053

0.069

1.35

1.75

A1

0.004

0.010

0.10

0.25

B

0.014

0.019

0.35

0.49

C

0.007

0.010

0.19

0.25

E

0.150

0.157

3.80

4.00

e

0.050

1.27

H

0.228

0.244

5.80

6.20

L

0.016

0.050

0.40

1.27






E



H


Narrow SO SMALL-OUTLINE PACKAGE

DIM

PINS

INCHES

MILLIMETERS

MIN

MAX

MIN

MAX

D

8

0.189

0.197

4.80

5.00

D

14

0.337

0.344

8.55

8.75

D

16

0.386

0.394

9.80

10.00








(0.150 in.)







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

© 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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Maxim Integrated:

MAX492CPA+ MAX492CSA+ MAX492ESA+ MAX494CPD+ MAX494CSD+ MAX494ESD+ MAX492CPA MAX492CSA MAX492CSA+T MAX492EPA MAX492EPA+ MAX492ESA MAX492ESA+T MAX494CPD MAX494CSD MAX494CSD+T MAX494EPD+ MAX494ESD MAX494ESD+T MAX492CSA-T MAX492ESA-T MAX494CSD-T MAX494ESD-T