General Description
The MAX4194 is a variable-gain precision instrumenta-
tion 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 fea-
ture 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 200mV below 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/MAX4196/MAX4197)
♦High Common-Mode Rejection: 115dB (G = +10V/V)
♦Input Common-Mode Range Extends 200mV
Below GND
♦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
REFVEE
1
2
8
7
RG+
VCC
IN-
IN+
RG-
SO
TOP VIEW
3
4
6
5
MAX4194
OUT
FBVEE
1
2
8
7
SHDN
VCC
IN-
IN+
REF
SO
3
4
6
5
MAX4195
MAX4196
MAX4197
19-1468; Rev 1; 6/03
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
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +5V, VEE = 0V, RL= 25kΩtied to VCC/2, VREF = VCC/2, TA= TMIN to TMAX, unless otherwise noted. Typical values are at
TA= +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 (VCC to VEE)..................................................+8V
All Other Pins .................................. (VCC + 0.3V) to (VEE - 0.3V)
Current into Any Pin..........................................................±30mA
Output Short-Circuit Duration (to VCC or VEE)........... Continuous
Continuous Power Dissipation (TA= +70°C)
8-Pin 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, 10s) ................................ +300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Single supply 2.7 7.5
Supply Voltage Range VCC Inferred by PSR test Dual supplies ±1.35 ±3.75 V
Quiescent Current ICC VIN+ = VIN- = VCC/2, VDIFF = 0V 93 110 µA
Shutdown Current ISHDN ISHDN = V
IL, M AX 4195/M AX 4196/M AX 4197 onl y 8 12 µA
G = +1V/V, VCM = VCC/2, TA = +25°C ±100 ±450
G = +10V/V, VCM = VCC/2, TA = +25°C ±75 ±225
G = +100V/V, VCM = VCC/2, TA = +25°C ±50 ±225
G = +1000V/V, VCM = VCC/2, TA = +25°C ±50
G = +1V/V, VCM = VCC/2, TA = TMIN to TMAX ±100 ±690
G = + 1V/V , V
C M
= V
C C
/2, TA = TM IN to TM AX ±75 ±345
G = + 100V /V, V
C M
= V
C C
/2, TA = TM IN to TM AX ±50 ±345
Input Offset Voltage VOS
G = + 1000V /V , VC M
= V
C C
/2, TA = TM IN to TM AX ±50
µV
G = +1V/V ±1.0 ±4.0
Input Offset Voltage Drift
(Note 1) TCVOS G ≥ +10V/V ±0.5 ±2.0 µV/°C
Differential 1000
Input Resistance RIN VCM = VCC/2 Common mode 1000 MΩ
Differential 1
Input Capacitance CIN VCM = VCC/2 Common mode 4 pF
Input Voltage Range VIN Inferred from CMR test VEE - 0.2 VCC - 1.1 V
G = +1V 66 78
G = +10V 80 94
V
C M
= V
E E
- 0.2V
to V
C C
- 1.1V ,
TA = + 25°C ,
∆RS = 1kΩ ( N ote 1) G = +100V 86 99
G = +1V 60 78
G = +10V 74 94
DC Common-Mode
Rejection CMRDC
V
C M
= V
E E
- 0.2V
to V
C C
- 1.1V ,
TA
= TM IN
to TM AX
,
∆RS = 1kΩ , ( N ote 1) G = +100V 77 99
dB
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V, VEE = 0V, RL= 25kΩtied to VCC/2, VREF = VCC/2, TA= TMIN to TMAX, unless otherwise noted. Typical values are at
TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
G = +1V 78 95
G = +10V 93 115
G = +100V/V 95 115
VCM = VEE + 0.2V
to VCC - 1.1V,
TA = +25°C,
∆RS = 1kΩG = + 1000V /V 115
G = +1V 73 95
G = +10V 88 115
G = +100V/V 90 115
DC Common-Mode
Rejection CMRDC
VCM = VEE + 0.2V
to VCC - 1.1V,
TA = TMIN to TMAX,
∆RS = 1kΩG = + 1000V /V 115
dB
G = +1V 85
G = +10V 101
AC Common-Mode
Rejection CMRAC
VCM = VEE + 0.2V
to VCC - 1.1V,
f = 120Hz G = +100V 106
dB
Power-Supply Rejection PSR
+2.7V ≤ VCC ≤ +7.5V; VCM = +1.5V;
VOUT = +1.5V; VREF = +1.5V; RL = 25kΩ to
+1.5V; G = +1V/V, +10V/V, +100V/V
90 120 dB
Input Bias Current IBVCM = VCC/2 6 20 nA
Input Bias Current Drift TCIB VCM = VCC/2 15 pA/°C
Input Offset Current IOS VCM = VCC/2 ±1.0 ±3.0 nA
Input Offset Current Drift TCIOS VCM = VCC/2 15 pA/°C
f = 10Hz 85
f = 100Hz 75
f = 10kHz 72
nV/√Hz
G = +1V/V
f = 0.1Hz to 10Hz 1.4 µVRMS
f = 10Hz 35
f = 100Hz 32
f = 10kHz 31
nV/√Hz
G = +10V/V
f = 0.1Hz to 10Hz 0.7 µVRMS
f = 10Hz 32
f = 100Hz 31
f = 10kHz 8.7
nV/√Hz
Input Noise Voltage en
G = +100V/V
f = 0.1Hz to 10Hz 0.6 µVRMS
f = 10Hz 2.4
f = 100Hz 0.76
f = 10kHz 0.1
pA/√Hz
Input Noise Current in
f = 0.1Hz to 10Hz 16 pARMS
VCC - VOH 30 100
RL = 25kΩ to VCC/2 VOL 30 100
VCC - VOH 100 200
Output Voltage Swing VOH, VOL
RL = 5kΩ to VCC/2 VOL 100 200
mV
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V, VEE = 0V, RL= 25kΩtied to VCC/2, VREF = VCC/2, TA= TMIN to TMAX, unless otherwise noted. Typical values are at
TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Short-Circuit Current
(Note 2) ISC ±4.5 mA
Gain Equation MAX4194 only 1 +
(50kΩ/RG)
G = +1V ±0.01 ±0.1
G = +10V ±0.03 ±0.3
G = +100V/V ±0.05 ±0.5
TA = +25°C,
VCM = VCC/2,
RL = 25kΩ,
VEE + 0.1V ≤ VOUT
≤ VCC - 0.1V G = + 1000V /V , M AX 4194 ±0.5
G = +1V ±0.01 ±0.1
G = +10V ±0.03 ±0.3
G = +100V/V ±0.05 ±0.5
Gain Error
TA = +25°C,
VCM = VCC/2,
RL = 5kΩ,
VEE + 0.2V ≤ VOUT
≤ VCC - 0.2V G = + 1000V /V , M AX 4194 ±0.5
%
MAX4194/MAX4195, G = +1V/V ±1 ±8
Gain Temperature
Coefficient (Note 1) MAX4196/MAX4197 ±1 ±15 ppm/°C
50kΩ Resistance
Temperature Coefficient
(Note 3)
TC50kΩMAX4194 ±16 ppm/°C
Nonlinearity
VEE + 0.1V ≤ VOUT ≤ VCC - 0.1V,
VCM = VCC/2, G = +1V/V, +10V/V,
+100V/V, +1000V/V
±0.001 %
Capacitive-Load Stability CL300 pF
MAX4194 250
G = +1V/V MAX4195 220
MAX4194 17
G = +10V/V MAX4196 34
MAX4194 1.5
G = +100V/V MAX4197 3.1
-3dB Bandwidth BW-3dB VOUT ≤ 0.1VP-P,
VCM = VCC/2
G = +1000V/V MAX4194 0.147
kHz
Slew Rate SR VOUT = 2VP-P, G = +1V/V 0.06 V/µs
G = +1V/V 0.05
G = +10V/V 0.04
G = +100V/V 5
Settling Time tS0.1%, VOUT = 2VP-P
G = +1000V/V 7
ms
Total Harmonic Distortion THD VOUT = 2VP-P, G = +1V/V, f = 1kHz 0.001 %
Input Logic Voltage High VIH VCC - 1.5 V
Input Logic Voltage Low VIL VCC - 2.5 V
SHDN Input Current VEE < VSHDN < VCC MAX4195/MAX4196/
MAX4197 only ±0.1 µA
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
_______________________________________________________________________________________ 5
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Time to Shutdown tSHDN G = +1V/V, 0.1%,
VOUT = +3V
MAX4195/MAX4196/
MAX4197 only 0.5 ms
Enable Time From
Shutdown tENABLE G = +1V/V, 0.1%,
VOUT = +3.5V
MAX4195/MAX4196/
MAX4197 only 0.5 ms
Power-Up Delay G = +1V/V, 0.1%, VOUT = +3.5V 1 ms
On/Off Settling Time tON/OFF VSHDN = VCC - 2.5V to VCC - 1.5V,
G = +100V/V, 0.1%, VOUT = +3.5V 0.5 ms
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 = 0V, RL= 25kΩtied to VCC/2, VREF = VCC/2, TA= TMIN to TMAX, unless otherwise noted. Typical values are at
TA= +25°C.)
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
(VOUT = 2Vp-p)
10k
10
1
1k
100
MAX4194 toc03
GAIN (V/V)
SETTLING TIME (µs)
Typical Operating Characteristics
(VCC = +5V, VEE = 0, RL= 25kΩtied 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= 25kΩtied 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
INPUT
(50mV/div)
OUTPUT
(50mV/div)
MAX4194
SMALL-SIGNAL PULSE RESPONSE
(GAIN = +1V/V)
MAX4194 toc07
20µs/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
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
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(VCC = +5V, VEE = 0, RL= 25kΩtied to VCC/2, TA = +25°C, unless otherwise noted.)
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
80
90
100
110
120
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX4194 toc14
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
25634 789
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
0
4
2
6
8
10
-40 10-15 35 60 85
INPUT BIAS CURRENT vs. TEMPERATURE
MAX4194TOC17
TEMPERATURE (°C)
INPUT BIAS CURRENT (nA)
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)
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
8 _______________________________________________________________________________________
FUNCTION
Pin Description
Typical Operating Characteristics (continued)
(VCC = +5V, VEE = 0, RL= 25kΩtied 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
VCC
SHDN
VEE
IN+
IN-
REF
1, 8 Connection for Gain-Setting Resistor—RG-, RG+
MAX4194
FUNCTION
MAX4195
MAX4196
MAX4197
NAME
PIN
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
_______________________________________________________________________________________ 9
Detailed Description
Input Stage
The MAX4194–MAX4197 family of low-power instru-
mentation amplifiers implements a three-amplifier topol-
ogy (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 pro-
vides 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-set-
ting 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 ampli-
fiers is VEE - 0.2V to VCC - 1.1V. Ideally, the instrumen-
tation 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 VREF. A differen-
tial voltage at IN+ (VIN+) and IN- (VIN-) develops an
identical voltage across the gain-setting resistor, caus-
ing a current (IG) to flow. This current also flows
through the feedback resistors of the two input ampli-
fiers A1 and A2, generating a differential voltage of:
VOUT2 - VOUT1 = IG · (R1+ RG+ R1)
where VOUT1 and VOUT2 are the output voltages of A1
and A2, RGis the gain-setting resistor (internal or exter-
nal to the part), and R1 is the feedback resistor of the
input amplifiers.
IGis determined by the following equation:
IG= (VIN+ - VIN-) / RG
The output voltage (VOUT) for the instrumentation
amplifier is expressed in the following equation:
VOUT = (VIN+ - VIN-) · [(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.
R1*
R1*
R2*
R2*
R2*
R2*
VIN-
REF
OUT
RG**
IG
IG
VIN+ VOUT2
VOUT1
VOUT2 - VOUT1
VIN+ - VIN-
A1
A2
A3
VOUT = (VIN+ - VIN-) ·
(
1 +
)
2R1
RG
* R1 = R2 = 25kΩ
** RG = INTERNAL TO MAX4195/MAX4196/MAX4197
RG = EXTERNAL TO MAX4194
Figure 3. Instrumentation Amplifier Configuration
25kΩ
25kΩ
25kΩ
25kΩ
25kΩ
25kΩ
IN-
RG-
OUT
REF
VEE
VCC
IN+
RG+
MAX4194
Figure 1. MAX4194 Simplified Block Diagram
25kΩ
25kΩ
25kΩ
25kΩ
25kΩ
25kΩ
IN-
SHDN
OUT
REF
VCC
VEE
FB
RG
IN+
MAX4195
MAX4196
MAX4197
Figure 2. MAX4195/MAX4196/MAX4197 Simplified Block
Diagram
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
10 ______________________________________________________________________________________
VCM vs. VOUT Characterization
Figure 4 illustrates the MAX4194 typical common-mode
input voltage range over output voltage swing at unity-
gain (pins 1 and 8 left floating), with a single-supply
voltage of VCC = +5V and a bias reference voltage of
VREF = 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 VOUT. For the higher gain
configurations, the VCM range will increase at the end-
points (B, C, E, and F) since a smaller differential volt-
age 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) resis-
tive load and still typically swing within 30mV of the
rails. With an output load of 5kΩtied to VCC/2, the out-
put 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/ RG
where G is the instrumentation amplifier’s gain and RG
is the gain-setting resistor.
The 50kΩresistor 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 feed-
back 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
VCC = +5V/+3V
VEE = 0
TA = +25°C
SHDN
(5V/div)
MAX4195
OUT
AC-COUPLED
(VDIFF = 2V,
G = +1V/V)
(500mV/div)
50µs/div
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
+100 511 510
+200 249 240
+500 100 100
+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
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
______________________________________________________________________________________ 11
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 RGval-
ues, which are required for high-gain operation, para-
sitic 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 sig-
nal. However, this alternative reduces gain accuracy
because RISO (Figure 6c) forms a potential divider with
the load resistor.
INPUT
(50mV/div)
OUTPUT
(50mV/div)
50µs/div
Figure 6b. Small-Signal Pulse Response with Excessive
Capacitive Load (RL= 25kΩ, CL= 1000pF)
INPUT
(50mV/div)
OUTPUT
(50mV/div)
50µs/div
Figure 6c. Small-Signal Pulse Response with Excessive
Capacitive Load and Isolating Resistor (RISO = 75Ω, RL=
25kΩ, CL= 1000pF)
IN-
(MAX4194)
(INTERNAL, MAX4195)
VEE
VREF VREF
VOUT
VCC
RISO
RLCL
IN+
RG = ∞
Figure 6a. Using a Resistor to Isolate a Capacitive Load from
the Instrumentation Amplifier (G = +1V/V)
SHDN
(5V/div)
MAX4196
OUT
AC-COUPLED
(VDIFF = 200mV,
G = +10V/V)
(500mV/div)
50µs/div
SHDN
(5V/div)
MAX4197
OUT
AC-COUPLED
(VDIFF = 20mV,
G = +100V/V)
(500mV/div)
50µs/div
Figure 5c. MAX4197 Shutdown Mode
Figure 5b. MAX4196 Shutdown Mode
MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
12 ______________________________________________________________________________________
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 fre-
quency response. To decrease stray capacitance, min-
imize 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 ther-
mocouples, PT100s, strain gauges (displacement sen-
sors), piezoresistive transducers (PRTs), flow sensors,
and bioelectrical applications. Figure 7 shows a simpli-
fied 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 (VBRIDGE). The low
impedance (120Ωto 350Ω) of the strain gauges, how-
ever, could cause significant voltage drop contributions
by the wires leading to the bridge, which would cause
excitation variations. Output voltage VOUT can be cal-
culated as follows:
VOUT = VAB · G
where G = (1 + 50kΩ/ RG) is the gain of the instrumen-
tation amplifier.
Since VAB is directly proportional to the excitation, gain
errors may occur.
Figure 7. Strain Gauge Connection to the MAX4194
IN-
VEE
VCC
VAB = VIN+ - VIN-
VBRIDGE R
R
RR
RG
IN+
RG+
RG-
OUT
REFERENCE
µP
REF
B
A
MAX144
ADC
R = 120Ω - 350Ω
___________________Chip Information
TRANSISTOR COUNT: 432
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
MAX4194–MAX4197
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.
13 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
SOICN .EPS
PACKAGE OUTLINE, .150" SOIC
1
1
21-0041 B
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
MAX
0.010
0.069
0.019
0.157
0.010
INCHES
0.150
0.007
E
C
DIM
0.014
0.004
B
A1
MIN
0.053A
0.19
3.80 4.00
0.25
MILLIMETERS
0.10
0.35
1.35
MIN
0.49
0.25
MAX
1.75
0.050
0.016L0.40 1.27
0.3940.386D
D
MINDIM
D
INCHES
MAX
9.80 10.00
MILLIMETERS
MIN MAX
16 AC
0.337 0.344 AB8.758.55 14
0.189 0.197 AA5.004.80 8
N MS012
N
SIDE VIEW
H 0.2440.228 5.80 6.20
e 0.050 BSC 1.27 BSC
C
HE
eBA1
A
D
0-8
L
1
VARIATIONS:
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)