General Description
The MAX4208/MAX4209 ultra-low offset and drift instrumen-
tation amplifiers feature exceptional precision specifications,
low power consumption, rail-to-rail output, excellent gain-
bandwidth product, and buffered REFIN/MODE input in a
very small μMAX® package. These devices use a spread-
spectrum, autozeroing technique that constantly measures
and corrects the input offset, eliminating drift over time
and temperature and the effect of 1/f noise. This technique
achieves less than 20μV offset voltage, allows ground-sens-
ing capability, provides ultra-low CMOS input bias current
and increased common-mode rejection performance.
The MAX4208/MAX4209 provide high-impedance inputs
optimized for small-signal differential voltages (±100mV).
All devices provide a gain-bandwidth product of 750kHz.
The MAX4208 provides an adjustable gain with two exter-
nal resistors or unity gain with FB connected to OUT. The
MAX4209 is available with a fixed gain of 100V/V with
±0.03% (typ) accuracy. Both devices include a reference
input (REF) to level-shift the output, allowing for bipolar sig-
nals in single-supply applications. In both devices, REFIN/
MODE is an input to a precision unity-gain buffer, which
sets the REF voltage to level-shift the output. The internal
REF buffer allows the reference to be set by a simple resis-
tive divider or an ADC reference without any loading error.
The MAX4208/MAX4209 operate with a 2.85V to 5.5V
single-supply voltage and consume only 750μA of qui-
escent current (when the internal buffer is off) and only
1.4μA in shutdown mode. These amplifiers also operate
with ±2.5V dual supplies with REF connected to ground
and REFIN/MODE to VSS. The MAX4208/MAX4209 are
available in space-saving 8-pin μMAX packages and
are specified over the automotive operating temperature
range (-40°C to +125°C).
Applications
● Strain-Gauge Ampliers
●Industrial Process Control
●Battery-Powered Medical Equipment
●Precision Low-Side Current Sense
●Notebook Computers
● Differential Voltage Amplication
Benets and Features
●Spread-Spectrum, Auto-Zero Instrumentation
Amplifiers Improve DC Characteristics to Maximize
Sensor Performance
• Input Offset Voltage: ±20μV (max) at +25°C
• ±0.25% (max) Gain Error
• Low 0.2μV/°C Offset Voltage Drift
• 1pA CMOS Input Bias Current
• True Ground Sensing with Rail-to-Rail Output
• 750kHz Gain-Bandwidth Product
●Buffered REF Input for High Accuracy and Bipolar
Operation
●Low Power Operation Supports Remote Sensing and
Battery-Powered Applications
• 2.85V to 5.5V Single-Supply Operation (or ±1.425V
to ±2.75V Dual Supplies)
• 750μA Supply Current
• 1.4μA Shutdown Mode
● Adjustable (MAX4208) and Fixed Gain of 100
(MAX4209) Provide Design Flexibility
μMAX is a registered trademark of Maxim Integrated Products, Inc.
19-0924; Rev 3; 5/15
Ordering Information
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
PART TEMP RANGE PIN-
PACKAGE
GAIN
(V/V)
MAX4208AUA+T -40°C to +125°C 8 µMAX ADJ
MAX4209HAUA+T -40°C to +125°C 8 µMAX 100
IN-
IN+
REFIN/MODE
REF
FB
MAX4208
R4
R3
VDD
VSS CFB
5V
OUT
REF
R2
FB
R1
G = 1 + R2
R1 BUFFER OUT =
VDD/2
VDD/2
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Amplifiers with REF Buffer
Typical Application Circuit
EVALUATION KIT AVAILABLE
VDD to VSS .............................................................. -0.3V to +6V
All Other Pins ................................(VSS - 0.3V) to (VDD + 0.3V)
OUT Short-Circuit Duration .......................................Continuous
Current Into OUT, VDD, and VSS .....................................±25mA
Current Into Any Other Pin ............................................... ±20mA
Continuous Power Dissipation (TA = +70°C)
μMAX (derate 4.5mW/°C above +70°C) .....................362mW
Operating Temperature Range ......................... -40°C to +125°C
Junction Temperature ...................................................... +150°C
Storage Temperature Range ............................ -65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = +25°C, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
INPUT DC CHARACTERISTICS
Input Offset Voltage VOS
MAX4208, G = 100V/V ±3 ±20 µV
MAX4209H, G = 100V/V ±3 ±20
Input Bias Current IB-100mV ≤ VDIFF ≤ +100mV (Note 3) 1 pA
Input Offset Current IOS -100mV ≤ VDIFF ≤ +100mV (Note 3) 1 pA
Input Resistance RIN VCM = VDD/2 Differential mode 2 GΩ
Common mode 2
Gain Error
-20mV ≤ VDIFF ≤ +20mV
MAX4208, G = 100V/V 0.05 ±0.25
%
-20mV ≤ VDIFF ≤ +20mV
MAX4209H, G = 100V/V 0.05 ±0.25
Gain Nonlinearity
(Note 2)
MAX4208, G = 100V/V 25 150 ppm
MAX4209H, G = 100V/V 25 150
Input Common-Mode Range VCM Guaranteed by CMRR test VSS - 0.1 VDD - 1.30 V
Input Common-Mode Rejection
Ratio CMRR VCM = (VSS - 0.1V) to (VDD - 1.30V) 106 135 dB
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Electrical Characteristics
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = +25°C, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Power-Supply Rejection Ratio PSRR VDD = 2.85V to 5.5V, VREF = VCM =
(VSS + 0.5V) 100 125 dB
REFIN/MODE AND REF DC CHARACTERISTICS
REFIN/MODE Buffer Input Offset
Voltage (Note 2) ±10 ±40 µV
REFIN/MODE Input Voltage Low VIL Reference buffer is OFF VSS VSS +
0.05 V
REFIN/MODE Input Voltage High VIH Shutdown mode VDD -
0.2 VDD V
REFIN/MODE Buffered
Reference Input Range
VREFIN/MODE
Reference buffer is ON, guaranteed by
REFIN/MODE CMRR test
VSS +
0.2
VDD -
1.3 V
REFIN/MODE Buffer
Common-Mode Rejection Ratio
(VSS + 0.2V) ≤ VREF/MODE ≤ (VDD - 1.3V)
(Note 2) 106 135 dB
REFIN/MODE Buffer
Power-Supply Rejection Ratio
VDD = 2.85V to 5.5V, VREF/MODE = VCM
= (VSS + 0.5V) 100 125 dB
REFIN/MODE Bias Current IREFIN VSS < VREFIN/MODE < VDD (Note 3) 1 pA
REF Common-Mode Range Guaranteed by reference CMRR test
(Note 4) VSS VDD -
1.30 V
REF Common-Mode Rejection
Ratio
VSS ≤ VREF ≤ (VDD - 1.30V)
(Note 4) 106 135 dB
REF, FB Bias Current MAX4208 (Note 3) 1 pA
REF Input Current (MAX4209) IREF
VDIFF = 0V (Note 5) ±10 nA
VDIFF = ±100mV (Note 5) ±100 µA
OUTPUT DC CHARACTERISTICS
Output Voltage Swing
(Notes 6 and 7)
VOH VDD - VOUT
RL = 100kΩ 30 45
mV
RL = 10kΩ 50 70
RL = 1kΩ 250 325
VOL VOUT - VSS
RL = 100kΩ 30 40
RL = 10kΩ 50 65
RL = 1kΩ 250 285
Short-Circuit Current ISC
Source +20 mA
Sink -25
Short-Circuit Recovery Time 0.50 ms
AC CHARACTERISTICS
Gain-Bandwidth Product GBW MAX4208, G = 1V/V 750 kHz
Small-Signal Bandwidth BW MAX4209H, G =100V/V 7.5 kHz
Slew Rate (Note 8) SR MAX4208, G = 1V/V, VOUT = 100mV step 80 V/ms
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Electrical Characteristics (continued)
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = +25°C, unless otherwise noted.) (Note 1)
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = -40°C to +125°C, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Settling Time tSTo within 0.1% of nal value
MAX4208,
G = 1V/V 10 µs
MAX4209H 120
Maximum Capacitive Load CLNo sustained oscillations 200 pF
Input Voltage Noise en
f = 0.1Hz to 10Hz 2.5 µVP-P
f = 1kHz 140 nV/√Hz
Power-Up Time To within 0.1% of nal value 20 ms
Shutdown Enable/Disable
Time tEN, tDIS 20 ms
POWER SUPPLY
Supply Voltage VDD Guaranteed by PSRR test 2.85 5.50 V
Supply Current IDD
VREFIN/MODE = VSS,
buffer OFF VDD = 5V 0.75 1.30
mA
(VSS + 0.2V) ≤ VREFIN/MODE ≤
(VDD - 1.3V), buffer ON VDD = 5V 1.40 2.30
VREFIN/MODE = VDD, shutdown mode 1.4 5.0 µA
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
INPUT DC CHARACTERISTICS
Input Offset Voltage VOS
MAX4208, G = 100V/V TA = +25°C to +85°C ±45
µV
TA = -40°C to +125°C ±60
MAX4209H, G = 100V/V TA = +25°C to +85°C ±30
TA = -40°C to +125°C ±40
Input Offset Voltage
Temperature Drift
(Note 2)
TCVOS
MAX4208, G = 100V/V TA = +25°C to +85°C 0.1 ±0.45
µV/°C
TA = -40°C to +125°C 0.1 ±0.45
MAX4209H, G = 100V/V TA = +25°C to +85°C 0.01 ±0.17
TA = -40°C to +125°C 0.01 ±0.17
Input Bias Current -100mV ≤ VDIFF < +100mV
(Note 3)
TA = +85°C 10 pA
TA = +125°C 20
Gain Error
MAX4208, G = 100V/V,
-20mV ≤ VDIFF ≤ +20mV
TA = +25°C to +85°C 0.30
%
TA = -40°C to +125°C 0.35
MAX4209H, G = 100V/V,
-20mV ≤ VDIFF ≤ +20mV
TA = +25°C to +85°C 0.30
TA = -40°C to +125°C 0.35
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Electrical Characteristics (continued)
Electrical Characteristics
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = -40°C to +125°C, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Gain Error Temperature
Drift (Note 2)
-20mV ≤ VDIFF ≤ +20mV
(MAX4208),
G = 100V/V
TA = -40°C to +125°C 50 180
ppm/°C
-20mV ≤ VDIFF ≤ +20mV
(MAX4209H),
G = 100V/V
TA = -40°C to +125°C 50 180
Gain Nonlinearity
(Note 2) GNL
MAX4208,
G = 100V/V
TA = +25°C to +85°C 210
ppm
TA = -40°C to +125°C 700
MAX4209H,
G = 100V/V
TA = +25°C to +85°C 210
TA = -40°C to +125°C 700
Input Common-Mode
Range VCM
Guaranteed by CMRR test,
TA = -40°C to +125°C VSS - 0.1 VDD - 1.6 V
Input Common-Mode
Rejection Ratio CMRR (VSS - 0.1V) ≤ VCM ≤
(VDD - 1.6V)
TA = +25°C to +85°C 96 dB
TA = -40°C to +125°C 90
Power-Supply Rejection
Ratio PSRR
VDD = 2.85V to 5.5V,
VREF = VCM = VSS +
0.5V
TA = +25°C to +85°C 96
dB
TA = -40°C to +125°C 90
REFIN/MODE AND REF DC CHARACTERISTICS
REFIN/MODE Buffer Input
Offset Voltage
TA = +25°C to +85°C 100 µV
TA = -40°C to +125°C 100
REFIN/MODE Buffered
Reference Input Range
VREFIN/MODE
Reference buffer is ON, guaranteed by REFIN/
MODE CMRR test VSS + 0.2 VDD - 1.6 V
REFIN/MODE Input
Voltage Low VIL Reference buffer is OFF VSS + 0.05 V
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Electrical Characteristics (continued)
Note 1: Specifications are 100% production tested at +25°C, unless otherwise noted. Limits over temperature are guaranteed by
design.
Note 2: Guaranteed by design. Thermocouple and leakage effects preclude measurement of this parameter during production test-
ing. Devices are screened during production testing to eliminate defective units.
Note 3: IN+ and IN- are gates to CMOS transistors with typical input bias current of 1pA. CMOS leakage is so small that it is impracti-
cal to test and guarantee in production. Max VDIFF is ±100mV. Devices are screened during production testing to eliminate
defective units. For the MAX4208, when there are no external resistors, the input bias current at FB and REF is 1pA (typ).
Note 4: Setting REF to ground (VSS) is allowed if the REF buffer is off. The unity-gain buffer is on when VREFIN/MODE is between
0.15V and (VDD - 1.3V). In this range, VREF = VREFIN/MODE ±40μV (maximum buffer input offset voltage over tempera-
ture). Setting REFIN/MODE to VDD puts the part in shutdown (IDD = 1.4μA).
Note 5: This is the REF current needed to directly drive the end terminal of the gain-setting resistors when REFIN/MODE is con-
nected to VSS to put the buffer in high-impedance mode. The REF input current is tested at the gain of 100. At gain 10 and
1000, IREF = ±100μA and 3.4μA, respectively at +25°C. See the Detailed Description.
Note 6: Output swing high (VOH) and output swing low (VOL) are measured only on G = 100 and G = 1000 devices. Devices with G
= 1 and G = 10 have output swing high limited by the range of VREF, VCM, and VDIFF (see the Output Swing section).
Note 7: Maximum range for VDIFF is from -100mV to +100mV.
Note 8: At G = 100V/V and G = 1000V/V, these instrumentation amplifiers are bandwidth limited and not capable of slew-rate-limited dV/dt.
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = -40°C to +125°C, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
REFIN/MODE Input-Voltage
High VIH MAX4208/MAX4209 in shutdown VDD - 0.2 V
REFIN/MODE Buffer
Common-Mode Rejection Ratio
(VSS + 0.2V)
≤ VREF ≤
(VDD - 1.6V)
TA = +25°C to +85°C 96
dB
TA = -40°C to +125°C 90
REF Common-Mode Range
(Note 4) Guaranteed by REF CMRR test VSS VDD - 1.6 V
REF Common-Mode Rejection
Ratio
VSS ≤ VREF ≤ (VDD -
1.6V)
TA = +25°C to +85°C 96 dB
TA = -40°C to +125°C 90
REFIN/MODE Buffer
Power-Supply Rejection Ratio
VDD = 2.85V to 5.5V,
VREFIN/MODE = VCM
= (VSS + 0.5V)
TA = +25°C to +85°C 96
dB
TA = -40°C to +125°C 90
OUTPUT DC CHARACTERISTICS
Output Voltage Swing (Note 6)
VOH VDD - VOUT
RL = 100kΩ 60
mV
RL = 10kΩ 90
RL = 1kΩ 375
VOL VOUT - VSS
RL = 100kΩ 50
RL = 10kΩ 75
RL = 1kΩ 325
POWER SUPPLY
Supply Voltage VDD Guaranteed by PSRR test 2.85 5.50 V
Supply Current
VREFIN/MODE = VSS,
buffer OFF VDD = 5V 1.70
mA
(VSS + 0.2V) ≤ VREFIN/MODE ≤
(VDD - 1.6V), buffer ON VDD = 5V 3.0
REFIN/MODE = VDD, shutdown mode 10 µA
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Electrical Characteristics (continued)
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = +25°C, unless otherwise noted.)
OFFSET VOLTAGE DRIFT HISTOGRAM
(TA = -20°C TO +85°C)
MAX4208/9 toc02
VOS DRIFT (nV/°C)
FREQUENCY (%)
0 50 100 150 200 250 300
25
0
20
15
10
5
-250-200-150-100 -50
GAIN ACCURACY HISTOGRAM
MAX4208/9 toc03
GAIN ACCURACY (%)
FREQUENCY (%)
0.250.200.150.100.050-0.05-0.10
50
45
40
35
30
25
20
15
10
5
0
-0.15
AV = +100V/V
-30
-20
-10
0
10
20
30
2.0 3.02.5 3.5 4.0 4.5 5.0 5.5 6.0
INPUT OFFSET VOLTAGE
vs. SUPPLY VOLTAGE
MAX4208/9 toc04
SUPPLY VOLTAGE (V)
INPUT OFFSET VOLTAGE (µV)
TA = -20°C TA = +25°C
TA = +85°C
TA = -40°C TA = +125°C
-30
-20
-10
0
10
20
30
-1 0 1 2 3 4
INPUT OFFSET VOLTAGE
vs. INPUT COMMON-MODE VOLTAGE
MAX4208/9 toc05
INPUT COMMON-MODE VOLTAGE (V)
INPUT OFFSET VOLTAGE (µV)
TA = -20°C TA = +25°C
TA = +85°C
TA = -40°C TA = +125°C
-30
-20
-10
0
10
20
30
0 1 2 3 4
INPUT OFFSET VOLTAGE
vs. REFIN COMMON-MODE (BUFFER ENABLED)
MAX4208/9 toc06
REFIN COMMON-MODE (V)
INPUT OFFSET VOLTAGE (µV)
TA = -20°CTA = -40°C
TA = +25°C
TA = +125°C TA = +85°C
-100
-40
-60
-80
-20
0
20
40
60
80
100
-30 -10-20 0 10 20 30
LINEARITY ERROR
vs. DIFFERENTIAL INPUT VOLTAGE
MAX4208/9 toc07
DIFFERENTIAL INPUT VOLTAGE (mV)
LINEARITY ERROR (ppm)
AV = +100V/V
INPUT OFFSET VOLTAGE HISTOGRAM
MAX4208/9 toc01
INPUT OFFSET VOLTAGE (µV)
FREQUENCY (%)
20151050-5-10-15
10
5
15
20
25
30
0
-20
AV = +100V/V
-20
0
40
20
60
80
10 1k100 10k 100k 1M 10M
GAIN vs. FREQUENCY
MAX4208/9 toc08
FREQUENCY (Hz)
GAIN (dB)
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX4208/9 toc09
FREQUENCY (Hz)
CMRR (dB)
10k 100k1k100
-120
-100
-80
-60
-40
-20
0
-140
10 1M
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Typical Operating Characteristics
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = +25°C, unless otherwise noted.)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX4208/9 toc10
FREQUENCY (Hz)
GAIN (dB)
10k 100k1k100
-120
-100
-80
-60
-40
-20
0
-140
10 1M
2.0
1.5
1.0
0.5
0
2.5 4.03.0 3.5 4.5 5.0 5.5
SUPPLY CURRENT (BUFFER ON)
vs. SUPPLY VOLTAGE
MAX4208/9 toc15
VDD (V)
IDD (mA)
VREFIN/MODE = VDD/2
TA = -40°C TA = +25°C TA = +125°C
MAX4208 INPUT-REFERRED NOISE
MAX4208/9 toc11
1s/div
1.2µV/div
0
2.0
1.0
4.0
3.0
5.0
6.0
2.5 3.5 4.03.0 4.5 5.0 5.5
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
MAX4208/9 toc16
VDD (V)
IDD (µA)
TA = -40°C
TA = +25°C
TA = +125°C
VREFIN/MODE = VDD
INPUT NOISE vs. FREQUENCY
MAX4208/9 toc12
FREQUENCY (Hz)
INPUT-NOISE DENSITY (nV/√Hz)
100 1k
10
100
1000
10,000
1
10 10k 100k
CFB = 1nF
CAPACITOR
CFB = 10nF
CAPACITOR
WHITE NOISE
140nV/Hz
0
0.3
0.6
0.9
1.2
1.5
0 2.0 2.51.0 1.50.5 3.0 3.5 4.0 4.5 5.0
IDD vs. VREFIN/MODE
MAX4208/9 toc13
VREFIN/MODE (V)
IDD (mA)
GREY = OUT OF
COMMON-MODE RANGE
INTERNAL BUFFER ON
VREFIN/MODE (VSS + 0.2V)
INTERNAL BUFFER OFF
VREFIN/MODE (VSS + 0.05V)
SHUTDOWN MODE
400
600
500
800
700
900
1000
2.5 3.5 4.03.0 4.5 5.0 5.5
SUPPLY CURRENT (BUFFER OFF)
vs. SUPPLY VOLTAGE
MAX4208/9 toc14
VDD (V)
IDD (µA)
VREFIN/MODE = VSS
TA = -40°C TA = +25°C
TA = +125°C
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Typical Operating Characteristics (continued)
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = +25°C, unless otherwise noted.)
LARGE-SIGNAL PULSE RESPONSE TIME
MAX4208/9 toc17
100µs/div
VIN+
5mV/div
OUTPUT
50mV/div
2.5V
2.5V
AV = 10V/V
VIN+ = 10mV STEP
VIN- = VREF = (VDD - VSS)/2
VREFIN/MODE = VSS
LARGE-SIGNAL PULSE RESPONSE TIME
MAX4208/9 toc18
400µs/div
VIN+
5mV/div
OUTPUT
500mV/div
2.5V
2.5V
AV = 100V/V
VIN+ = 10mV STEP
VIN- = VREF = (VDD - VSS)/2
VREFIN/MODE = VSS
LARGE-SIGNAL PULSE RESPONSE TIME
MAX4208/9 toc19
400µs/div
VIN+
1mV/div
OUTPUT
1V/div
2.5V
2.5V
AV = 1000V/V
VIN+ = 2mV STEP
VIN- = VREF = (VDD - VSS)/2
VREFIN/MODE = VSS
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Typical Operating Characteristics (continued)
(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100kΩ to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for
G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA = +25°C, unless otherwise noted.)
PIN NAME FUNCTION
1 REFIN/MODE
Reference/Shutdown Mode Input. Trimode function is as follows:
Connect to VDD to put the device in shutdown mode.
Connect to an external reference (between VSS + 0.2V and VDD - 1.3V) to buffer the voltage at
REFIN/MODE. Using the REF buffer allows the use of a simple resistor-divider or high-impedance
external reference to set the OUT level at 0mV IN with minimum error.
Connect to VSS to force the internal buffer output into a high-impedance state to allow external direct
drive of REF.
2 IN- Negative Differential Input
3 IN+ Positive Differential Input
4VSS Negative Supply Input. Bypass VSS to ground with a 0.1µF capacitor or connect to ground for
single-supply operation.
5 REF Output Reference Level. REF sets the OUT voltage for zero differential input. The internal buffer
sets the voltage at REF when the voltage at REFIN/MODE is between VSS + 0.2V and VDD - 1.3V.
6FB
Feedback Input. Connect FB to the center tap of an external resistive divider from OUT to REF to
set the gain for the MAX4208. MAX4209 FB is internally connected to gain-setting resistors. Connect
an optional capacitor, CFB, from OUT to FB to reduce autozero noise.
7 OUT Amplier Output
8VDD Positive Supply Input. Bypass VDD to ground with a 0.1µF capacitor.
0.1% SETTLING TIME
vs. GAIN
MAX4208/9 toc21
GAIN (V/V)
SETTLING TIME (µs)
10 100
100
1000
10,000
10
1 1000
SETTLING TIME
vs. ACCURACY
MAX4208/9 toc22
ACCURACY (%)
SETTLING TIME (µs)
0.10
20
40
60
80
100
120
140
160
180
0
0.01 1.00
G = 100
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
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Typical Operating Characteristics (continued)
Pin Description
Detailed Description
The MAX4208/MAX4209 family of instrumentation ampli-
fiers implements a spread-spectrum, autozeroing tech-
nique that minimizes the input offset error, drift over
time and temperature, and the effect of 1/f noise. Unlike
the traditional three-op amp instrumentation amplifier,
this technique allows true ground-sensing capability
combined with a low input bias current and increased
common-mode rejection.
The differential input signal is converted to a current by
an input transconductance stage. An output transconduc-
tance stage converts a portion of the output voltage (equal
to the output voltage divided by the gain) into another pre-
cision current. These two currents are subtracted and the
result is fed to a loop amplifier with sufficient gain to mini-
mize errors (Figures 1 and 2). The MAX4209 has a facto-
ry-trimmed gain of 100V/V. The MAX4208 has an adjust-
able gain, set with an external pair of resistors between
OUT, FB, and REF (Figure 1). The MAX4208/MAX4209
have an output reference input (REF) that is connected to
an external reference for bipolar operation of the device.
For single-supply operation, the range for VREF is 0V to
(VDD - 1.3V). Although full output-swing capability and
maximum symmetrical dynamic range is obtained at REF
= VDD/2, the optimal VREF setting depends on the supply
voltage and output-voltage swing needed by the appli-
cation. The maximum recommended differential input
voltage is ±100mV. Linearity and accuracy are degraded
above that level. The MAX4208/MAX4209 operate with
single 2.85V to 5.5V supply voltages or dual ±1.425V to
±2.75V supplies.
The MAX4208/MAX4209 have a shutdown feature to
reduce the supply current to 1.4μA (typ) when REFIN/
MODE is connected to VDD.
REF, REFIN/MODE, and Internal REFIN
Buffer of the MAX4208/MAX4209
In a single-supply system, bipolar operation of an instru-
mentation amplifier requires the application of a voltage
reference (REF) to set the output voltage level when a
zero differential voltage is applied to the input. The output
swing is around this reference level, which is usually set
to half of the supply voltage for the largest swing and
dynamic range.
In many instrumentation amplifiers, the gain-setting resis-
tors as well as the RL are connected between OUT and
REF. OUT can sink and source current but the need for
REF to sink and source current is often overlooked and
can lead to significant errors. Therefore, the MAX4208/
MAX4209 include a REFIN buffer, an internal, precision
unity-gain buffer on-chip to sink and source the currents
needed at REF without loading the reference voltage
supplied at REFIN/MODE.
Figure 2. MAX4209 Functional DiagramFigure 1. MAX4208 Functional Diagram
MAX4208
gmgm
AMP
SHDN
+1
OUT
FB
REF
REFIN/MODE
R2
R1
IN-
IN+
VDD
VSS
G = 1 + R2
R1
MAX4209
gmgm
AMP
SHDN
+1
OUT
FB
REF
REFIN/MODE
R2
R1
IN-
IN+
VDD
VSS
G = 1 + R2
R1
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In a conventional instrumentation amplifier, a simple
method to apply a reference voltage is the use of a volt-
age-divider to set the REF level (often halfway between
ground and VDD). The voltage-divider should be made of
higher value resistors to minimize current consumption,
but the sinking and sourcing current from the load and
gain-setting resistors create a significant commonmode
signal at the divider midpoint. The MAX4208/MAX4209
precision REFIN buffer essentially eliminates the error
voltage at REF.
The REFIN buffer is a unity-gain op amp that has a guar-
anteed VOS of less than 40μV with a CMOS input bias
current of only 1pA, to allow setting REFIN with a simple
resistive divider with minimum errors.
REFIN/MODE is a triple function input (see Table 1). To
use the internal REFIN buffer, connect REFIN/MODE to an
external reference or a simple resistive divider at any volt-
age between (VSS + 0.2V) and (VDD - 1.3V). These volt-
ages represent the minimum and maximum for the REFIN
buffer’s input common-mode range (see the Electrical
Characteristics table). To use ground at REF or to use an
external low-impedance reference directly at REF without
the internal REFIN buffer, connect REFIN/MODE to VSS.
This disables the REFIN buffer, dropping the IDD to 750μA
and puts the REFIN buffer output in a high-impedance
state to allow external direct drive of REF. To put the
MAX4208/MAX4209 into shutdown and reduce the supply
current to less than 5μA, drive REFIN/MODE to VDD.
Note: When driving REF directly, REFIN/MODE must be
at VSS and shutdown mode is NOT available.
Input Differential Signal Range
The MAX4208/MAX4209 feature a proprietary input
structure optimized for small differential signals of up to
±100mV. The output of the MAX4208/MAX4209 allows
for bipolar input signals. The output voltage is equal to
the voltage at REF for zero differential input. The gain
accuracy of these devices is laser trimmed to better than
0.1% (typ).
Output Swing
The MAX4208/MAX4209 are designed specifically for
small input signals (±100mV) from sensors, strain gaug-
es, etc. These instrumentation amplifiers are capable of
rail-to-rail output-voltage swings; however, depending
on the selected gain and REF level, the rail-to-rail output
swing may not be required or desired.
For example, consider single-supply operation of the
MAX4208 in a unity-gain configuration with REF connect-
ed to a voltage at half of the supply voltage (VDD/2). In this
case, the output-voltage swing would be ±100mV around
the REF level and would not need to reach either rail.
Another example is the MAX4209H (gain internally set
to 100) also operating with a single-supply voltage and
REF set externally to ground (VSS). REFIN/MODE must
also be connected to ground (VSS). In this case, an input
voltage of 0 to 10mV differential would ideally drive an
output-voltage swing of 0 to 1V. However, the output
swing can only get to within 40mV of ground (VSS) (see
the VOL specifications in the Electrical Characteristics
table). It is recommended that for best accuracy and
linearity, the lowest differential input voltage for unipolar
operation is usually picked to be a nonzero value (e.g.,
0.5mV or more).
Another remedy is to use REFIN/MODE of 250mV (see
the REFIN/MODE Buffered Reference Input Range in
the Electrical Characteristics table), which causes a 0 to
100mV input to start OUT at 250mV and swing to 1.25V,
to prevent the output from going into its bottom nonlinear
range. An ADC with differential input can be connected
between OUT and REF to record the true 0 to 1V swing.
Devices with higher gain and bipolar output swing can be
configured to approach either rail for maximum dynamic
range. However, as the output approaches within VOL or
VOH of the supply voltages, the linearity and accuracy
degrades, especially under heavy loading.
Table 1. REFIN/MODE Pin Functions
*See the Electrical Characteristics table for detailed specifications.
REFIN/MODE VOLTAGE* STATE OF MAX4208/MAX4209 and REFIN BUFFER
VDD (typically +5V) The entire IC is in SHDN mode and draws 1.4µA of supply current.
Between VSS + 200mV and
(VDD - 1.3V)
The internal REF buffer is activated. REF MUST NOT be fed by any external source. The voltage
at REFIN/MODE is transferred to REF within ±40FV, max (VOS of the internal REF buffer).
VSS (typically ground)
The internal REF buffer is OFF with its output in a high-impedance state to allow direct drive of
REF (or connection to ground). REF must be directly connected to an external voltage reference
capable of sinking and sourcing the load current.
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Applications Information
Setting the Gain (MAX4208)
Connect a resistive divider from OUT to REF with the cen-
ter tap connected to FB to set the gain for the MAX4208
(see the Typical Application Circuit). Calculate the gain
using the following formula:
R2
GAIN 1 R1
= +
Choose a value for R1 ≤ 1kΩ. Resistor accuracy ratio
directly affects gain accuracy. Resistor sum less than
10kΩ should not be used because their loading can
slightly affect output accuracy.
Input Common Mode vs.
Input Differential-Voltage Range
Traditional three-op amp instrumentation amplifiers have
a defined relationship between the maximum input dif-
ferential voltage and maximum input common-mode
voltage that arises from saturation of intermediate ampli-
fier stages. This correlation is frequently represented
as a hexagon graph of input common-mode voltage vs.
output voltage for the instrumentation amplifier shown in
Figure 3. Application limitations hidden in this graph are:
●The input common-mode voltage range does not
include the negative supply rail, and so no amplifica-
tion is possible for inputs near ground for single-supply
applications.
●Input differential voltages can be amplified with maxi-
mum gain only over a limited range of input common-
mode voltages (i.e., range of y-axis for max range of
x-axis is limited).
●If large amplitude common-mode voltages need to
be rejected, differential voltages cannot be amplified
with a maximum gain possible (i.e., range of x-axis
for a maximum range of y-axis is limited). As a conse-
quence, a secondary high-gain amplifier is required to
follow the front-end instrumentation amplifier.
The indirect current-feedback architecture of the
MAX4208/MAX4209 instrumentation amplifiers do not
suffer from any of these drawbacks. Figure 4 shows the
input common-mode voltage vs. output voltage graph of
indirect current-feedback architecture.
In contrast to three-op amp instrumentation amplifiers, the
MAX4208/MAX4209 features:
●The input common-mode voltage range, which
includes the negative supply rail and is ideal for single-
supply applications.
●Input differential voltages that can be amplified with
maximum gain over the entire range of input common-
mode voltages.
●Large common-mode voltages that can be rejected at
the same time differential voltages are amplified with
maximum gain, and therefore, no secondary ampli-
fier is required to follow the front-end instrumentation
amplifier.
Gain Error Drift Over Temperature
Adjustable gain instrumentation amplifiers typically use a
single external resistor to set the gain. However, due to
differences in temperature drift characteristics between
the internal and external resistors, this leads to large
gain-accuracy drift over temperature. The MAX4208 is an
adjustable gain instrumentation amplifier that uses two
external resistors to set its gain. Since both resistors are
external to the device, layout and temperature coefficient
matching of these parts deliver a significantly more stable
gain over operating temperatures.
The fixed gain, MAX4209H has both internal resistors for
excellent matching and tracking.
Use of External Capacitor CFB
for Noise Reduction
Zero-drift chopper amplifiers include circuitry that continu-
ously compensates the input offset voltage to deliver pre-
cision and ultra-low temperature drift characteristics. This
self-correction circuitry causes a small additional noise
contribution at its operating frequency (a psuedorandom
clock around 45kHz for MAX4208/MAX4209). For high-
bit resolution ADCs, external filtering can significantly
attenuate this additional noise. Simply adding a feedback
capacitor (CFB) between OUT and FB reduces high-
frequency gain, while retaining the excellent precision
DC characteristics. Recommended values for CFB are
between 1nF and 10nF. Additional anti-aliasing filtering
at the output can further reduce this autocorrection noise.
Capacitive-Load Stability
The MAX4208/MAX4209 are capable of driving capacitive
loads up to 200pF. Applications needing higher capacitive
drive capability may use an isolation resistor between
OUT and the load to reduce ringing on the output signal.
However, this reduces the gain accuracy due to the volt-
age drop across the isolation resistor.
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Power-Supply Bypass and Layout
Good layout technique optimizes performance by decreas-
ing the amount of stray capacitance at the instrumenta-
tion amplifier’s gain-setting pins (OUT, FB, and REF).
Excess capacitance produces peaking in the amplifier’s
frequency response. To decrease stray capacitance,
minimize trace lengths by placing external components
as close as possible to the instrumentation amplifier.
Unshielded long traces at the inputs of the instrumenta-
tion amplifier degrade the CMRR and pick-up noise. This
produces inaccurate output in highgain configurations.
Use shielded or coax cables to connect the inputs of the
instrumentation amplifier. Since the MAX4208/MAX4209
feature ultra-low input offset voltage, board leakage
and thermocouple effects can easily introduce errors in
the input offset voltage readings when used with high-
impedance signal sources. Minimize board leakage cur-
rent and thermocouple effects by thoroughly cleaning the
board and placing the matching components very close
to each other and with appropriate orientation. For best
performance, bypass each power supply to ground with a
separate 0.1μF capacitor.
For noisy digital environments, the use of multilayer PCB
with separate ground and power-supply planes is recom-
mended. Keep digital signals far away from the sensitive
analog inputs.
Refer to the MAX4208 or MAX4209 Evaluation Kit data
sheets for good layout examples.
Low-Side Current-Sense Amplier
The use of indirect current-feedback architecture makes
the MAX4208/MAX4209 ideal for low-side current-sens-
ing applications, i.e., where the current in the circuit
ground needs to be measured by means of a small sense
resistor. In these situations, the input common-mode
voltage is allowed to be at or even slightly below ground
(VSS - 0.1V).
If the currents to be measured are bidirectional, connect
REFIN/MODE to VDD/2 to get full dynamic range for each
direction. If the currents to be measured are unidirec-
tional, both REFIN/MODE and REF can be tied to GND.
However, VOL limitations can limit low-current measure-
ment. If currents need to be measured down to 0A, bias
REFIN/MODE to a voltage above 0.2V to activate the
internal buffer and to stay above amplifier VOL, and mea-
sure both OUT and REF with a differential input ADC.
Low-Voltage, High-Side
Current-Sense Amplier
Power management is a critical area in high-performance
portable devices such as notebook computers. Modern
digital processors and ASICs are using smaller transis-
tor geometries to increase speed, reduce size, and also
lower their operating core voltages (typically 0.9V to
1.25V). The MAX4208/MAX4209 instrumentation ampli-
fiers can be used as a nearly zero voltage-drop, current-
sense amplifier (see Figure 5).
Figure 3. Limited Common Mode vs. Output Voltage of a
Three Op-Amp INA
Figure 4. Input Common Mode vs. Output Voltage of
MAX4208/MAX4209 Includes 0V (GND)
VCM
VCC
VCM-MAX
3/4 VCC
1/2 VCC
1/4 VCC
0
VCC/2 VCC
VOUT
( = GAIN x VDIFF + VREF)
VREF = 1/2 VCC
CLASSIC THREE OP-AMP INA VCM
VDD
VCM-MAX
0VDD/2 VDD
VOUT
( = GAIN x VDIFF + VREF)
VREF = 1/2 VDD
MAX4208/MAX4209
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The ultra-low VOS of the MAX4208/MAX4209 allows
full-scale VSENSE of only 10mV to 20mV for minimally
invasive current sensing using milliohm sense resistors
to get high accuracy. Previous methods used the internal
resistance of the inductor in the step-down DC-DC con-
verter to measure the current, but the accuracy was only
20% to 30%. Using a full-scale VSENSE of 20mV, a 20μV
max, VOS error term is less than 0.1% and MAX4209H
gain error is 0.25% max at 100x, so the total accuracy is
greatly improved. The 0 to 2V output of MAX4209H can
be sent to an ADC for calculation. The adjustable gain
of MAX4208, can be set to a gain of 250x using 1kΩ
and 249kΩ resistors, to scale up a lower 10mV VSENSE
voltage to a larger 2.5V output voltage for wider dynamic
range as needed.
Figure 5. MAX4208/MAX4209 Used as Precision Current-Sense Amplifiers for Notebook Computers with VSENSE of 20mV
ASIC
IN+
IN-
REF
VSS
VDD
REFIN/MODE
1V AT 10A
ADC
ANTI-ALIASING
FILTER
0.002Ω
+VSENSE-
MAX4209H
OUT
+3.3V
VSENSE = 10A x 0.002Ω = 20mV
POWER IN RSENSE = 10A x 20mV = 200mW
OUT = G x 20mV = 100 x 20mV = 2V
IN-
IN+
REFIN/MODE
REF
FB
MAX4208
R4
R3
VDD
VSS CFB
5V
OUT
REF
R2
FB
R1
G = 1 + R2
R1 BUFFER OUT =
VDD/2
VDD/2
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Typical Application Circuit
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN
NO.
8 μMAX U8+1 21-0036 90-0092
TOP VIEW
FB
REFVSS
1
2
8
7
VDD
OUTIN-
IN+
REFIN/MODE
µMAX
3
4
6
5
MAX4208
MAX4209
+
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Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
Chip Information
PROCESS: BiCMOS
Pin Conguration
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 9/07 Initial release —
1 4/09 Removed future products 1–5, 11, 12,
13
2 5/14 Removed reference to “automotive transducer applications” from the Applications 1
3 5/15 Added the Benets and Features section 1
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
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Revision History
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