Datasheet MAX4196ESA, MAX4195ESA, MAX4194ESA, MAX4197ESA Datasheet (Maxim)

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General Description

The MAX4194 is a variable-gain precision instrumenta­tion amplifier that combines Rail-to-Rail®single-supply
operation, outstanding precision specifications, and a
high gain bandwidth. This amplifier is also offered in
three fixed-gain versions: the MAX4195 (G = +1V/V),
the MAX4196 (G = +10V/V), and the MAX4197 (G =
+100V/V). The fixed-gain instrumentation amplifiers fea­ture a shutdown function that reduces the quiescent
current to 8µA. A traditional three operational amplifier
configuration is used to achieve maximum DC preci­sion.

The MAX4194–MAX4197 have rail-to-rail outputs and
inputs that can swing to within 200mV of the negative rail
and to within 1.1V of the positive rail. All parts draw only
93µA and operate from a single +2.7V to +7.5V supply
or from dual ±1.35V to ±3.75V supplies. These amplifiers
are offered in 8-pin SO packages and are specified for
the extended temperature range (-40°C to +85°C).

See the MAX4198/MAX4199 data sheet for single-sup­ply, precision differential amplifiers.

Applications

Medical Equipment
Thermocouple Amplifier
4–20mA Loop Transmitters
Data-Acquisition Systems
Battery-Powered/Portable Equipment
Transducer Interface
Bridge Amplifier

Features

♦ +2.7V Single-Supply Operation
♦ Low Power Consumption

93µA Supply Current
8µA Shutdown Current (MAX4195/96/97)

♦ High Common-Mode Rejection: 115dB (G = +10V/V)
♦ Low 50µV Input Offset Voltage (G ≥ +100V/V)
♦ Low ±0.01% Gain Error (G = +1V/V)
♦ 250kHz -3dB Bandwidth (G = +1V/V, MAX4194)
♦ Rail-to-Rail Outputs

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,

Precision Instrumentation Amplifiers

________________________________________________________________

Maxim Integrated Products

1

OUT

REFV

EE

1
2

87RG+

V

CC

IN-

IN+

RG-

SO

TOP VIEW

3

4

6

5

MAX4194

OUT

FBV

EE

1
2

87SHDN

V

CC

IN-

IN+

REF

SO

3

4

6

5

MAX4195
MAX4196
MAX4197

19-1468; Rev 0; 4/99

PART

MAX4194ESA
MAX4195ESA
MAX4196ESA

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

8 SO
8 SO
8 SO

Pin Configurations

Ordering Information

MAX4197ESA

-40°C to +85°C 8 SO

PART

MAX4194
MAX4195
MAX4196 Yes

Yes

No

SHUTDOWN GAIN (V/V)

Variable

+1

+10

MAX4197 Yes +100

Selector Guide

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

CMRR (dB)

95 (G = +1V/V)

95
115
115

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +5V, VEE= 0, RL= 25kΩ tied to VCC/2, V

REF

= VCC/2, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at

T

A

= +25°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.

Supply Voltage (VCCto VEE)..................................................+8V

All Other Pins ..................................(VCC+ 0.3V) to (VEE- 0.3V)

Current into Any Pin..........................................................±30mA

Output Short-Circuit Duration (to VCCor VEE)........... Continuous

Continuous Power Dissipation (TA= +70°C)

SO (derate 5.9mW/°C above +70°C)........................... 471mW

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

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

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

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

I

SHDN

= VIL, MAX4195/96/97 only µA

Inferred by PSR

test

VCM= VEE+ 0.2V
to VCC- 1.1V,
f = 120Hz

VCM= VEE+ 0.2V
to VCC- 1.1V,
TA= T

MIN

to T

MAX

,

∆RS= 1kΩ

115

VCM= VCC/2

Differential

90 115

VCM= VEE+ 0.2V
to V

CC

- 1.1V,

T

A

= +25°C,

∆R

S

= 1kΩ

G = +1V/V

Common mode

VIN+ = VIN- = VCC/2, V

DIFF

= 0

G = +1V/V, VCM= VCC/2, TA= +25°C

Inferred from CMR test

VCM= VCC/2

CONDITIONS

106

101

dB

85

CMR

AC

AC Common-Mode Rejection

88 115

115

G = +1V/V

73 95

G = +10V/V

95 115

G = +100V/V

G = +1V/V
G = +10V/V

93 115

G = +100V/V
G = +1000V/V

dB

78 95

CMR

DC

DC Common-Mode Rejection

VVEE+ 0.2 VCC- 1.1V

IN

Input Voltage Range

Differential

1000

Common mode 4

812

I

SHDN

Shutdown Current

V

±1.35 ±3.75

pF

2.7 7.5

V

CC

Supply Voltage Range

1

MΩ

1000

R

IN

Input Resistance

C

IN

Input Capacitance

G = +1V/V
G = +10V/V

µV/°C

±1.0 ±4.0

TC

VOS

Input Offset Voltage Drift
(Note 1)

µA

93 110

I

CC

Quiescent Current

G = +100V/V

±100 ±450

G = +1000V/V

UNITSMIN TYP MAXSYMBOLPARAMETER

Single supply
Dual supplies

G ≥ +10V/V ±0.5 ±2.0

G = +10V/V, VCM= VCC/2, TA= +25°C

±75 ±225

G = +1000V/V, VCM= VCC/2, TA= +25°C

±50

G = +100V/V, VCM= VCC/2, TA= +25°C

±50 ±225

G = +10V/V, VCM= VCC/2, TA= T

MIN

to T

MAX

±75 ±345

G = +1V/V, VCM= VCC/2, TA= T

MIN

to T

MAX

G = +1000V/V, VCM= VCC/2, TA= T

MIN

to

µVV

OS

Input Offset Voltage

±50

G = +100V/V, VCM= VCC/2, TA= T

MIN

to

±50 ±345

±100 ±690

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,

Precision Instrumentation Amplifiers

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +5V, VEE= 0, RL= 25kΩ tied to VCC/2, V

REF

= VCC/2, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at

T

A

= +25°C.)

VCM= VCC/2

VCM= VCC/2

+2.7V ≤ VCC≤ +7.5V; VCM= +1.5V;
V

OUT

= +1.5V; V

REF

= +1.5V; RL= 25kΩ to

+1.5V; G = +1V/V, +10V/V, +100V/V

RL= 25kΩ to VCC/2

MAX4194 only

f = 0.1Hz to 10Hz

f = 10kHz

VCM= VCC/2

f = 10Hz

RL= 5kΩ to VCC/2

f = 100Hz

CONDITIONS

±0.01 ±0.1

1+ (50kΩ/RG)Gain Equation

mA±4.5I

SC

Short-Circuit Current (Note 2)

mV

100 200

VOH, V

OL

Output Voltage Swing

100 200

nA±1.0 ±3.0I

OS

Input Offset Current

pA/°C15TC

IB

dB90 120PSRPower-Supply Rejection

Input Bias Current Drift

30 100

30 100

pA

RMS

16

i

n

Input Noise Current

pA√Hz

0.1

pA/°C15TC

IOS

Input Offset Current Drift

85

2.4

0.76

UNITSMIN TYP MAXSYMBOLPARAMETER

f = 10Hz

75f = 100Hz

nV√Hz

72f = 10KHz

G = +1V/V

µV

RMS

1.4f = 0.1Hz to 10Hz
35f = 10Hz
32f = 100Hz

nV√Hz

31f = 10KHz

G = +10V/V

µV

RMS

0.7f = 0.1Hz to 10Hz
32f = 10Hz
31f = 100Hz

nV√Hz

8.7f = 10KHz

G = +100V/V

µV

RMS

0.6

e

n

Input Noise Voltage

f = 0.1Hz to 10Hz

VCC- V

OH

V

OL

VCC- V

OH

V

OL

G = +1V/V
G = +10V/V ±0.03 ±0.3

TA= +25°C,
VCM= VCC/2,
RL= 25kΩ,
VEE+ 0.1V ≤ V

OUT

≤ VCC- 0.1V

G = +1000V/V, MAX4194 ±0.5

G = +100V/V ±0.05 ±0.5

G = +10V/V ±0.03 ±0.3

TA= +25°C,
VCM= VCC/2,
RL= 5kΩ,
VEE+ 0.2V ≤ V

OUT

≤ VCC- 0.2V

G = +1000V/V, MAX4194

G = +1V/V

%

±0.5

Gain Error

G = +100V/V ±0.05 ±0.5

±0.01 ±0.1

VCM= VCC/2 nA620I

B

Input Bias Current

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers

4 _______________________________________________________________________________________

Note 1: Guaranteed by design.
Note 2: Maximum output current (sinking/sourcing) in which the gain changes by less than 0.1%.
Note 3: This specification represents the typical temperature coefficient of an on-chip thin film resistor. In practice, the temperature

coefficient of the gain for the MAX4194 will be dominated by the temperature coefficient of the external gain-setting resistor.

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +5V, VEE= 0, RL= 25kΩ tied to VCC/2, V

REF

= VCC/2, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at

T

A

= +25°C.)

V

SHDN

= VCC- 2.5V to VCC- 1.5V, G = +100V/V,

0.1%, V

OUT

= +3.5V

G = +1V/V, 0.1%, V

OUT

= +3.5V

MAX4196/MAX4197

G = +1V/V, 0.1%,
V

OUT

= +3.5V

MAX4194/MAX4195, G = +1V/V

G = +1V/V, 0.1%,
V

OUT

= +3V

VEE< V

SHDN

< V

CC

V

OUT

= 2Vp-p, G = +1V/V, f = 1kHz

V

OUT

= 2Vp-p, G = +1V/V

MAX4194

VEE+ 0.1V ≤ V

OUT

≤ VCC- 0.1V, VCM= VCC/2,

G = +1V/V, +10V/V, +100V/V, +1000V/V

0.1%, V

OUT

= 2Vp-p

CONDITIONS

ms0.5t

ON/OFF

On/Off Settling Time

ms1Power-Up Delay

ms0.5t

ENABLE

Enable Time From Shutdown

ms0.5t

SHDN

Time to Shutdown

µA±0.1

SHDN Input Current

VVCC- 2.5V

IL

Input Logic Voltage Low

VVCC- 1.5V

IH

Input Logic Voltage High

%0.001THDTotal Harmonic Distortion

ms

7

t

S

Settling Time

5

ppm/°C±16

ppm/°C

±1 ±15

±1 ±8

Gain Temperature Coefficient
(Note 1)

0.04

0.05

V/µs0.06SRSlew Rate

250

TC

50kΩ

50kΩ Resistance Temperature
Coefficient (Note 3)

%±0.001Nonlinearity

pF300C

L

Capacitive Load Stability

UNITSMIN TYP MAXSYMBOLPARAMETER

MAX4194

G = +1V/V

MAX4195 220
MAX4194

G = +10V/V

MAX4196

17
34

MAX4194 1.5

G = +100V/V

MAX4197

G = +1000V/V

V

OUT

≤ 0.1Vp-p,

VCM= VCC/2

MAX4194

kHz

3.1

0.147

BW-

3dB

-3dB Bandwidth

G = +1V/V
G = +10V/V
G = +100V/V
G = +1000V/V

MAX4195/MAX4196/
MAX4197 only

MAX4195/MAX4196/
MAX4197 only

MAX4195/MAX4196/
MAX4197 only

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,

Precision Instrumentation Amplifiers

_______________________________________________________________________________________

5

100 1k 10k 100k 1M

MAX4194

SMALL-SIGNAL GAIN vs. FREQUENCY

MAX4194 toc01-1

FREQUENCY (Hz)

-6

-5

-4

-3

-2

-1

0

1

2

3

4

NORMALIZED GAIN (dB)

G = +100V/V

G = +10V/V

G = +1V/V

100 1k 10k 100k 1M

MAX4195/MAX4196/MAX4197

SMALL-SIGNAL GAIN vs. FREQUENCY

MAX4194 toc02-2

FREQUENCY (Hz)

G = +100V/V

G = +10V/V

G = +1V/V

-6

-5

-4

-3

-2

-1

0

1

2

3

4

NORMALIZED GAIN (dB)

11k10010

0.1% SETTLING TIME vs. GAIN
(V

OUT

= 2Vp-p)

10k

10

1

1k

100

MAX4194 toc03

GAIN (V/V)

SETTLING TIME (µs)

INPUT
(500mV/div)

OUTPUT
(500mV/div)

MAX4194

LARGE-SIGNAL PULSE RESPONSE

(GAIN = +1V/V)

MAX4194 toc04

20µs/div

INPUT
(50mV/div)

OUTPUT
(50mV/div)

MAX4194

SMALL-SIGNAL PULSE RESPONSE

(GAIN = +1V/V)

MAX4194 toc07

20µs/div

INPUT
(5mV/div)

OUTPUT
(500mV/div)

MAX4194

LARGE-SIGNAL PULSE RESPONSE

(GAIN = +100V/V)

MAX4194 toc05

200µs/div

INPUT
(5mV/div)

OUTPUT
(500mV/div)

MAX4197

LARGE-SIGNAL PULSE RESPONSE

(GAIN = +100V/V)

MAX4194 toc06

200µs/div

INPUT
(500µV/div)

OUTPUT
(50mV/div)

MAX4194

SMALL-SIGNAL PULSE RESPONSE

(GAIN = +100V/V)

MAX4194 toc08

200µs/div

INPUT
(500µV/div)

OUTPUT
(50mV/div)

MAX4197

SMALL-SIGNAL PULSE RESPONSE

(GAIN = +100V/V)

MAX4194 toc09

200µs/div

Typical Operating Characteristics

(VCC= +5V, VEE= 0, RL= 25kΩ tied to VCC/2, TA = +25°C, unless otherwise noted.)

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VCC= +5V, VEE= 0, RL= 25kΩ tied to VCC/2, TA = +25°C, unless otherwise noted.)

0

-100

-120

-140
1 10 100 1k 10k 100k

POWER-SUPPLY REJECTION

vs. FREQUENCY

-80

MAX4194 toc10

FREQUENCY (Hz)

PSR (dB)

-60

-40

-20
G = +1V/V

G = +100V/V

G = +1000V/V

G = +10V/V

-30

-120

COMMON-MODE REJECTION

vs. FREQUENCY

-100

-110

MAX4194 toc11

FREQUENCY (Hz)

CMR (dB)

-80

-90

-70

-60

-50

-40

10 100 1k 10k 100k

G = +1V/V

G = +100V/V

G = +1,000V/V

G = +10V/V

1 10 100 1k 10k 100k

VOLTAGE-NOISE DENSITY

vs. FREQUENCY

MAX4194 toc12

FREQUENCY (Hz)

VOLTAGE NOISE DENSITY (nV/÷Hz)

1,000

1

10

100

G = +1V/V

G = +100V/V

G = +1000V/V

G = +10V/V

MAX4195/MAX4196

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. FREQUENCY

MAX4194 toc13

THD + NOISE (%)

1.000

0

0.001

0.010

0.100

1 10 100 1k 10k

FREQUENCY (Hz)

G = +1V/V
MAX4195

MAX4196
G = +10V/V

84

86

90

88

94

96

92

98

-40

-15 10 35 60

85

SUPPLY CURRENT vs. TEMPERATURE

MAX4194 toc15

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

G = +1000V/V

G = +1V/V, +10V/V

G = +100V/V

80

90

100

110

120

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX4194 toc14

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

25634 789

0

2

6

4

8

10

-40

-15 10 35 60

85

MAX4195/MAX4196/MAX4197

SHUTDOWN CURRENT vs. TEMPERATURE

MAX4194 toc16

TEMPERATURE (°C)

SHUTDOWN CURRENT (µA)

0

4

2

6

8

10

-40 10-15 35 60 85

INPUT BIAS CURRENT vs. TEMPERATURE

MAX4194TOC17

TEMPERATURE (°C)

INPUT BIAS CURRENT (nA)

FUNCTION

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,

Precision Instrumentation Amplifiers

_______________________________________________________________________________________ 7

Pin Description

Typical Operating Characteristics (continued)

(VCC= +5V, VEE= 0, RL= 25kΩ tied to VCC/2, TA = +25°C, unless otherwise noted.)

-200

-100

-150

-50

0

50

-40 10-15 35 60 85

INPUT OFFSET CURRENT vs. TEMPERATURE

MAX4194TOC18

TEMPERATURE (°C)

INPUT OFFSET CURRENT (pA)

MAX4196

MAX4197

MAX4195

-100

-25

-50

-75

50
25

0

75

100

-40 10-15 35 60 85

INPUT OFFSET VOLTAGE vs. TEMPERATURE

MAX4194TOC19

TEMPERATURE (°C)

INPUT OFFSET VOLTAGE (µV)

MAX4197

MAX4196

MAX4195

MAX4194
(G = +10V/V)

MAX4194
(G = +100V/V,
G = +1000V/V)

Feedback. Connects to OUT.5—
Amplifier Output66
Positive Supply Voltage77
Shutdown Control8—

Negative Supply Voltage44

Noninverting Input33

Inverting Input22

Reference Voltage. Offsets output voltage.15

FB
OUT
V

CC

SHDN

V

EE

IN+

IN-

REF

1, 8 Connection for Gain Setting Resistor— RG-, RG+

MAX4194

FUNCTION

MAX4195
MAX4196
MAX4197

NAME

PIN

Detailed Description

Input Stage

The MAX4194–MAX4197 family of low-power instru­mentation amplifiers implements a three-amplifier topol­ogy (Figure 1). The input stage is composed of two
operational amplifiers that together provide a fixed-gain
differential and a unity common-mode gain. The output
stage is a conventional differential amplifier that pro­vides an overall common-mode rejection of 115dB (G =

+10V/V). The MAX4194’s gain can be externally set
between +1V/V and +10,000V/V (Table 1). The
MAX4195/MAX4196/MAX4197 have on-chip gain-set­ting resistors (Figure 2), and their gains are fixed at
+1V/V, +10V/V, and +100V/V, respectively.

Input Voltage Range

and Detailed Operation

The common-mode input range for all of these ampli­fiers is VEE+ 0.2V to VCC- 1.1V. Ideally, the instrumen­tation amplifier (Figure 3) responds only to a differential
voltage applied to its inputs, IN+ and IN-. If both inputs
are at the same voltage, the output is V

REF

. A differen-

tial voltage at IN+ (V

IN+

) and IN- (V

IN-

) develops an
identical voltage across the gain-setting resistor, caus­ing a current (IG) to flow. This current also flows
through the feedback resistors of the two input ampli­fiers A1 and A2, generating a differential voltage of:

V

OUT2

- V

OUT1

= IG · (R1+ RG+ R1)

where V

OUT1

and V

OUT2

are the output voltages of A1
and A2, RGis the gain-setting resistor (internal or exter­nal to the part), and R1 is the feedback resistor of the
input amplifiers.

IGis determined by the following equation:

IG= (V

IN+

- V

IN-

) / R

G

The output voltage (V

OUT

) for the instrumentation

amplifier is expressed in the following equation:

V

OUT

= (V

IN+

- V

IN-

) · [(2 · R1) / RG] + 1

The common-mode input range is a function of the
amplifier’s output voltage and the supply voltage. With
a power supply of VCC, the largest output signal swing
can be obtained with REF tied to VCC/2. This results in
an output voltage swing of ±VCC/2. An output voltage
swing less than full-scale increases the common-mode
input range.

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers

8 _______________________________________________________________________________________

R1*

R

1

*

R

2

*

R

2

*

R

2

*

R

2

*

V

IN-

REF

OUT

R

G

**

I

G

I

G

V

IN+

V

OUT2

V

OUT1

V

OUT2

- V

OUT1

V

IN+

- V

IN-

A1

A2

A3

V

OUT

= (V

IN+

- V

IN-

) · (1 +

)

2R1

R

G

* R1 = R2 = 25kΩ
** R

G

= INTERNAL TO MAX4195/MAX4196/MAX4197

R

G

= EXTERNAL TO MAX4194

Figure 3. Instrumentation Amplifier Configuration

25k

25k

25k

25k

25k

25k

IN-

RG-

OUT

REF
V

EE

V

CC

IN+

RG+

MAX4194

Figure 1. MAX4194 Simplified Block Diagram

25k

25k

25k

25k

25k

25k

IN-

SHDN

OUT

REF

V

CC

V

EE

FB

R

G

IN+

MAX4195
MAX4196
MAX4197

Figure 2. MAX4195/MAX4196/MAX4197 Simplified Block
Diagram

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,

Precision Instrumentation Amplifiers

_______________________________________________________________________________________ 9

V

CM

vs. V

OUT

Characterization

Figure 4 illustrates the MAX4194 typical common-mode
input voltage range over output voltage swing at unity­gain (pins 1 and 8 left floating), with a single-supply
voltage of VCC= +5V and a bias reference voltage of
V

REF

= VCC/2 = +2.5V. Points A and D show the full
input voltage range of the input amplifiers (VEE+ 0.2V
to VCC- 1.1V) since, with +2.5V output, there is zero
input differential swing. The other points (B, C, E, and
F) are determined by the input voltage range of the
input amps minus the differential input amplitude nec­essary to produce the associated V

OUT

. For the higher
gain configurations, the VCMrange will increase at the
endpoints (B, C, E, and F) since a smaller differential
voltage is necessary for the given output voltage.

Rail-to-Rail Output Stage

The MAX4194–MAX4197’s output stage incorporates a
common-source structure that maximizes the dynamic
range of the instrumentation amplifier.

The output can drive up to a 25kΩ (tied to VCC/2) resis­tive load and still typically swing within 30mV of the
rails. With an output load of 5kΩ tied to VCC/2, the out­put voltage swings within 100mV of the rails.

Shutdown Mode

The MAX4195–MAX4197 feature a low-power shutdown
mode. When the shutdown pin (SHDN) is pulled low,
the internal amplifiers are switched off and the supply
current drops to 8µA typically (Figures 5a, 5b, and 5c).

This disables the instrumentation amplifier and puts its
output in a high-impedance state. Pulling SHDN high
enables the instrumentation amplifier.

Applications Information

Setting the Gain (MAX4194)

The MAX4194’s gain is set by connecting a single,
external gain resistor between the two RG pins (pin 1
and pin 8), and can be described as:

G = 1 + 50kΩ / R

G

where G is the instrumentation amplifier’s gain and R

G

is the gain-setting resistor.
The 50kΩ resistor of the gain equation is the sum of the

two resistors internally connected to the feedback loops
of the IN+ and IN- amplifiers. These embedded feed­back resistors are laser trimmed, and their accuracy
and temperature coefficients are included in the gain
and drift specification for the MAX4194.

0

1

3

2

4

5

021 345

OUTPUT VOLTAGE (V)

COMMON-MODE INPUT VOLTAGE (V)

B

C

0.03 4.97

D

A

F

E

MAX4194/MAX4195
G = +1V/V
REF = +2.5V/+1.5V

V

CC

= +5V/+3V

V

EE

= 0

T

A

= +25°C

Figure 4. Common-Mode Input Voltage vs. Output Voltage

Figure 5a. MAX4195 Shutdown Mode

*

Leave pins 1 and 8 open for G = +1V/V.

GAIN (V/V)

CLOSEST RG (1%)

(Ω)

CLOSEST RG(5%)

(Ω)

+1 ∞ * ∞ *
+2 49.9k 51k

+5 12.4k 12k
+10 5.62k 5.6k
+20 2.61k 2.7k
+50 1.02k 1.0k

[phone]
[phone]

[phone]
+1,000 49.9 51
+2,000 24.9 24
+5,000 10 10

+10,000 4.99 5.1

Table 1. MAX4194 External Gain Resistor
Selection

50µs/div

MAX4195
OUT
AC-COUPLED

= 2V,

(V

DIFF

G = +1V/V)
(500mV/div)

SHDN
(5V/div)

The accuracy and temperature drift of the RGresistors
also influence the IC’s precision and gain drift, and can
be derived from the equation above. With low RGval­ues, which are required for high-gain operation, para­sitic resistances may significantly increase the gain
error.

Capacitive Load Stability

The MAX4194–MAX4197 are stable for capacitive loads
up to 300pF (Figure 6a). Applications that require
greater capacitive-load driving capability can use an
isolation resistor (Figure 6b) between the output and
the capacitive load to reduce ringing on the output sig­nal. However, this alternative reduces gain accuracy
because R

ISO

(Figure 6c) forms a potential divider with

the load resistor.

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers

10 ______________________________________________________________________________________

INPUT
(50mV/div)

OUTPUT
(50mV/div)

50µs/div

Figure 6b. Small-Signal Pulse Response with Excessive
Capacitive Load (R

L

= 25kΩ, CL= 1000pF)

INPUT
(50mV/div)

OUTPUT
(50mV/div)

50µs/div

Figure 6c. Small-Signal Pulse Response with Excessive
Capacitive Load and Isolating Resistor (R

ISO

= 75Ω, RL=

25k

Ω

, CL= 1000pF)

IN-

(MAX4194)
(INTERNAL, MAX4195)

V

EE

V

REF

V

REF

V

OUT

V

CC

R

ISO

R

L

C

L

IN+

R

G

= ∞

Figure 6a. Using a Resistor to Isolate a Capacitive Load from
the Instrumentation Amplifier (G = +1V/V)

SHDN
(5V/div)

MAX4196
OUT
AC-COUPLED
(V

DIFF

= 200mV,
G = +10V/V)
(500mV/div)

50µs/div

Figure 5c. MAX4197 Shutdown Mode

Figure 5b. MAX4196 Shutdown Mode

MAX4197
OUT
AC-COUPLED

= 20mV,

(V

DIFF

G = +100V/V)
(500mV/div)

SHDN
(5V/div)

50µs/div

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,

Precision Instrumentation Amplifiers

______________________________________________________________________________________ 11

Power-Supply Bypassing and Layout

Good layout technique optimizes performance by
decreasing the amount of stray capacitance at the
instrumentation amplifier’s gain-setting pins. Excess
capacitance will produce peaking in the amplifier’s fre­quency response. To decrease stray capacitance, min­imize trace lengths by placing external components as
close to the instrumentation amplifier as possible. For
best performance, bypass each power supply to
ground with a separate 0.1µF capacitor.

Transducer Applications

The MAX4194–MAX4197 instrumentation amplifiers can
be used in various signal-conditioning circuits for ther­mocouples, PT100s, strain gauges (displacement sen­sors), piezoresistive transducers (PRTs), flow sensors,
and bioelectrical applications. Figure 7 shows a simpli­fied example of how to attach four strain gauges (two

identical two-element strain gauges) to the inputs of the
MAX4194. The bridge contains four resistors, two of
which increase and two of which decrease by the same
ratio.

With a fully balanced bridge, points A (IN+) and B (IN-)
see half the excitation voltage (V

BRIDGE

). The low
impedance (120Ω to 350Ω) of the strain gauges, how­ever, could cause significant voltage drop contributions
by the wires leading to the bridge, which would cause
excitation variations. Output voltage V

OUT

can be cal-

culated as follows:

V

OUT

= VAB· G

where G = (1 + 50kΩ / RG) is the gain of the instrumen­tation amplifier.

Since VABis directly proportional to the excitation, gain
errors may occur.

Figure 7. Strain Gauge Connection to the MAX4194

IN-

V

EE

V

CC

V

AB

= V

IN+

- V

IN-

V

BRIDGE

R

R

R

R

R

G

IN+

RG+

RG-

OUT

REFERENCE

µP

REF

B

A

MAX144

ADC

R = 120Ω - 350Ω

___________________Chip Information

TRANSISTOR COUNT: 432

MAX4194–MAX4197

Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers

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.

12

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Package Information