MAX4208AUA+T - Hytronics

General Description

The MAX4208/MAX4209 ultra-low offset and drift instru-

mentation amplifiers feature exceptional precision specifi-

cations, 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-sensing capability, pro-

vides 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

external 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

signals 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 resistive 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 quiescent 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 auto-

motive operating temperature range (-40°C to +125°C).

Applications

Automotive Transducer Applications

Strain-Gauge Amplifiers

Industrial Process Control

Battery-Powered Medical Equipment

Precision Low-Side Current Sense

Notebook Computers

Differential Voltage Amplification

Features

♦Ultra-Low 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

♦Buffered REF Input for High Accuracy and

Bipolar Operation

♦2.85V to 5.5V Single-Supply Operation

(or ±1.425V to ±2.75V Dual Supplies)

♦750µA Supply Current

♦1.4µA Shutdown Mode

♦750kHz Gain-Bandwidth Product

♦Operate Over the -40°C to +125°C Automotive

Temperature Range

♦Tiny 8-Pin µMAX Package

Note: All 8-pin µMAX packages have package code U8-1.

+Denotes a lead(Pb)-free/RoHS-compliant package.

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

19-0924; Rev 1; 4/09

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

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

µMAX is a registered trademark of Maxim Integrated Products, Inc.

IN-

IN+

REFIN/MODE

REF

MAX4208

VDD

VSS CFB

OUT

REF

G = 1 + R2

R1 BUFFER OUT =

VDD/2

Typical Application Circuit

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for

G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA= +25°C, unless otherwise noted.) (Note 1)

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.

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)

8-Pin 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

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

INPUT DC CHARACTERISTICS

MAX4208, G = 100V/V ±3 ±20

Input Offset Voltage VOS MAX4209H, G = 100V/V ±3 ±20 µV

Input Bias Current IB-100mV ≤ VDIFF ≤ +100mV (Note 3) 1 pA

Input Offset Current IOS -100mV ≤ VDIFF ≤ +100mV (Note 3) 1 pA

Differential mode 2

Input Resistance RIN VCM = VDD/2 Common mode 2 GΩ

-20mV ≤ VDIFF ≤ +20mV

MAX4208, G = 100V/V 0.05 ±0.25

Gain Error

-20mV ≤ VDIFF ≤ +20mV

MAX4209H, G = 100V/V 0.05 ±0.25

MAX4208, G = 100V/V 25 150

Gain Nonlinearity

(Note 2) MAX4209H, G = 100V/V 25 150 ppm

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 Amplifiers with REF Buffer

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto 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 VRE F IN /M OD E 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

VDIFF = 0V (Note 5) ±10 nA

REF Input Current (MAX4209) IREF VDIFF = ±100mV (Note 5) ±100 µA

OUTPUT DC CHARACTERISTICS

RL = 100kΩ30 45

RL = 10kΩ50 70VOH VDD - VOUT

RL = 1kΩ250 325

RL = 100kΩ30 40

RL = 10kΩ50 65

Output-Voltage Swing

(Notes 6 and 7)

VOL VOUT - VSS

RL = 1kΩ250 285

Source +20

Short-Circuit Current ISC Sink -25 mA

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 Amplifiers with REF Buffer

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto 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

MAX4208,

G = 1V/V 10

Settling Time tSTo within 0.1% of final

value MAX4209H 120

µs

Maximum Capacitive Load CLNo sustained oscillations 200 pF

f = 0.1Hz to 10Hz 2.5 µVP-P

Input-Voltage Noise enf = 1kHz 140 nV/√Hz

Power-Up Time To within 0.1% of final 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

VREFIN/MODE = VSS,

buffer OFF VDD = 5V 0.75 1.30

(VSS + 0.2V) ≤ VREFIN/MODE

≤ (VDD - 1.3V), buffer ON VDD = 5V 1.40 2.30

Supply Current IDD

VREFIN/MODE = VDD, shutdown mode 1.4 5.0 µA

ELECTRICAL CHARACTERISTICS

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto 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

INPUT DC CHARACTERISTICS

TA = +25°C to +85°C ±45

MAX4208, G = 100V/V TA = -40°C to +125°C ±60

TA = +25°C to +85°C ±30

Input Offset Voltage VOS

MAX4209H, G = 100V/V TA = -40°C to +125°C ±40

µV

TA = +25°C to +85°C 0.1 ±0.45

MAX4208, G = 100V/V TA = -40°C to +125°C 0.1 ±0.45

TA = +25°C to +85°C 0.01 ±0.17

Input Offset Voltage

Temperature Drift

(Note 2)

TCVOS

MAX4209H, G = 100V/V TA = -40°C to +125°C 0.01 ±0.17

µV/°C

TA = +85°C 10

Input Bias Current (Note 3)

-100m V ≤ VDIFF < +100m VTA = +125°C 20 pA

TA = +25°C to +85°C 0.30

M AX 4208, G = 100V /V ,

- 20m V ≤ V

D IF F ≤ + 20m V TA = -40°C to +125°C 0.35

TA = +25°C to +85°C 0.30

Gain Error

M AX 4209H , G = 100V /V ,

- 20m V ≤ V

D IF F ≤ + 20m V TA = -40°C to +125°C 0.35

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS (continued)

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto 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

-20mV ≤ VDIFF ≤

+20mV (MAX4208),

G = 100V/V

TA = -40°C to

+125°C 50 180

Gain Error Temperature Drift

(Note 2) -20mV ≤ VDIFF ≤

+20mV (MAX4209H),

G = 100V/V

TA = -40°C to

+125°C 50 180

ppm/°C

TA = +25°C to +85°C 210

MAX4208,

G = 100V/V TA = -40°C to +125°C 700

TA = +25°C to +85°C 210

Gain Nonlinearity

(Note 2) GNL

MAX4209H,

G = 100V/V TA = -40°C to +125°C 700

ppm

Input Common-Mode Range VCM Guaranteed by CMRR test,

TA = -40°C to +125°C

VSS -

0.1

VDD -

1.6 V

TA = + 25°C to + 85° C 96

Input Common-Mode Rejection

Ratio CMRR (VSS - 0.1V) ≤ VCM ≤

(VDD - 1.6V) TA = -40°C to

+125°C 90 dB

TA = + 25°C to + 85° C 96

Power-Supply Rejection Ratio PSRR

VDD = 2.85V to 5.5V,

VREF = VCM = VSS +

0.5V

TA = -40°C to

+125°C 90 dB

REFIN/MODE AND REF DC CHARACTERISTICS

TA = +25°C to +85°C 100

REFIN/MODE Buffer Input

Offset Voltage TA = -40°C to +125°C 100 µV

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 Amplifiers with REF Buffer

6 _______________________________________________________________________________________

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 testing.

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 impractical 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 temperature). 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 connected 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.

ELECTRICAL CHARACTERISTICS (continued)

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto 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

TA = +25°C to +85°C 96

REFIN/MODE Buffer

Common-Mode Rejection Ratio

(VSS + 0.2V)

≤ VREF ≤

(VDD - 1.6V) TA = -40°C to +125°C 90

REF Common-Mode Range

(Note 4) Guaranteed by REF CMRR test VSS VDD -

1.6 V

TA = +25°C to +85°C 96

REF Common-Mode Rejection

Ratio

VSS ≤ VREF ≤ (VDD -

1.6V) TA = - 40°C to + 125°C 90 dB

TA = +25°C to +85°C 96

REFIN/MODE Buffer

Power-Supply Rejection Ratio

D D

= 2.85V to 5.5V ,

VREFIN/MODE = VCM

= (VSS + 0.5V) TA = - 40°C to + 125°C 90

OUTPUT DC CHARACTERISTICS

RL = 100kΩ60

RL = 10kΩ90VOH VDD - VOUT

RL = 1kΩ375

RL = 100kΩ50

RL = 10kΩ75

Output-Voltage Swing (Note 6)

VOL VOUT - VSS

RL = 1kΩ325

POWER SUPPLY

Supply Voltage VDD Guaranteed by PSRR test 2.85 5.50 V

VREFIN/MODE = VSS,

buffer OFF VDD = 5V 1.70

(VSS + 0.2V) ≤ VREFIN/MODE ≤

(VDD - 1.6V), buffer ON VDD = 5V 3.0

Supply Current

REFIN/MODE = VDD, shutdown mode 10 µA

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

_______________________________________________________________________________________ 7

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

-250-200-150-100-50

GAIN ACCURACY HISTOGRAM

MAX4208/9 toc03

GAIN ACCURACY (%)

FREQUENCY (%)

0.250.200.150.100.050-0.05-0.10

-0.15

AV = +100V/V

-30

-20

-10

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°CTA = +25°C

TA = +85°C

TA = -40°CTA = +125°C

-30

-20

-10

01234

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°CTA = +85°C

Typical Operating Characteristics

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for

G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA= +25°C, unless otherwise noted.)

INPUT OFFSET VOLTAGE HISTOGRAM

MAX4208/9 toc01

INPUT OFFSET VOLTAGE (μV)

FREQUENCY (%)

20151050-5-10-15

-20

AV = +100V/V

-30

-20

-10

-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°CTA = +25°C

TA = +85°C

TA = -40°CTA = +125°C

-100

-40

-60

-80

-20

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

-20

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

-140

10 1M

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

8 _______________________________________________________________________________________

POWER-SUPPLY REJECTION RATIO

vs. FREQUENCY

MAX4208/9 toc10

FREQUENCY (Hz)

GAIN (dB)

10k 100k1k100

-120

-100

-80

-60

-40

-20

-140

10 1M

INPUT NOISE vs. FREQUENCY

MAX4208/9 toc12

FREQUENCY (Hz)

INPUT-NOISE DENSITY (nV/√Hz)

100 1k

100

1000

10,000

10 10k 100k

CFB = 1nF

CAPACITOR

CFB = 10nF

CAPACITOR

WHITE NOISE

140nV/√Hz

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°CTA = +25°C

TA = +125°C

MAX4208 INPUT-REFERRED NOISE

MAX4208/9 toc11

1s/div

1.2μV/div

Typical Operating Characteristics (continued)

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for

G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA= +25°C, unless otherwise noted.)

2.0

1.5

1.0

0.5

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°CTA = +25°CTA = +125°C

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

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

_______________________________________________________________________________________ 9

LARGE-SIGNAL PULSE RESPONSE TIME

MAX4208/9 toc17

100μs/div

VIN+

5mV/div

OUTPUT

50mV/div

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

AV = 100V/V

VIN+ = 10mV STEP

VIN- = VREF = (VDD - VSS)/2

VREFIN/MODE = VSS

Typical Operating Characteristics (continued)

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto 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 toc19

400μs/div

VIN+

1mV/div

OUTPUT

1V/div

2.5V

AV = 1000V/V

VIN+ = 2mV STEP

VIN- = VREF = (VDD - VSS)/2

VREFIN/MODE = VSS

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

10 ______________________________________________________________________________________

Pin Description

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

SS 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 Amplifier Output

DD 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

1 1000

SETTLING TIME

vs. ACCURACY

MAX4208/9 toc22

ACCURACY (%)

SETTLING TIME (μs)

0.10

100

120

140

160

180

0.01 1.00

G = 100

Typical Operating Characteristics (continued)

(VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL= 100kΩto VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for

G = 100V/V (R1 = 1kΩ, R2 = 99kΩ), TA= +25°C, unless otherwise noted.)

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

______________________________________________________________________________________ 11

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 com-

bined with a low input bias current and increased com-

mon-mode rejection.

The differential input signal is converted to a current by

an input transconductance stage. An output transcon-

ductance stage converts a portion of the output voltage

(equal to the output voltage divided by the gain) into

another precision current. These two currents are sub-

tracted and the result is fed to a loop amplifier with suffi-

cient gain to minimize errors (Figures 1 and 2). The

MAX4209 has a factory-trimmed gain of 100V/V. The

MAX4208 has an adjustable 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 bipo-

lar operation of the device. For single-supply operation,

the range for VREF is 0V to (VDD - 1.3V). Although full out-

put-swing capability and maximum symmetrical dynamic

range is obtained at REF = VDD/2, the optimal VREF set-

ting depends on the supply voltage and output-voltage

swing needed by the application. The maximum recom-

mended 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

instrumentation 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

resistors as well as the RLare connected between OUT

and REF. OUT can sink and source current but the

need for REF to sink and source current is often over-

looked 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.

MAX4208

gmgm

AMP

SHDN

OUT

REF

REFIN/MODE

IN-

IN+

VDD

VSS

G = 1 + R2

Figure 1. MAX4208 Functional Diagram

MAX4209

gmgm

AMP

SHDN

OUT

REF

REFIN/MODE

IN-

IN+

VDD

VSS

G = 1 + R2

Figure 2. MAX4209 Functional Diagram

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

12 ______________________________________________________________________________________

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 consump-

tion, but the sinking and sourcing current from the load

and gain-setting resistors create a significant common-

mode 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 voltage between (VSS + 0.2V) and (VDD - 1.3V).

These voltages 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, con-

nect 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 exter-

nal 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

gauges, 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 con-

nected 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 volt-

age 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 with-

in VOL or VOH of the supply voltages, the linearity and

accuracy degrades, especially under heavy loading.

Table 1. REFIN/MODE Pin Functions

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 ±40µV, 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.

*See the Electrical Characteristics table for detailed specifications.

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

______________________________________________________________________________________ 13

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:

Choose a value for R1 ≤1kΩ. Resistor accuracy ratio

directly affects gain accuracy. Resistor sum less than

10kΩshould 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 differential voltage and maximum input common-

mode voltage that arises from saturation of intermediate

amplifier stages. This correlation is frequently repre-

sented as a hexagon graph of input common-mode

voltage vs. output voltage for the instrumentation ampli-

fier 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 amplifi-

cation is possible for inputs near ground for single-

supply applications.

• Input differential voltages can be amplified with

maximum 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 con-

sequence, 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 sin-

gle-supply applications.

• Input differential voltages that can be amplified with

maximum gain over the entire range of input com-

mon-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

amplifier is required to follow the front-end instru-

mentation 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 coeffi-

cient 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 con-

tinuously compensates the input offset voltage to deliver

precision and ultra-low temperature drift characteristics.

This self-correction circuitry causes a small additional

noise contribution at its operating frequency (a psuedo-

random clock around 45kHz for MAX4208/MAX4209).

For high-bit resolution ADCs, external filtering can signif-

icantly attenuate this additional noise. Simply adding a

feedback capacitor (CFB) between OUT and FB

reduces high-frequency gain, while retaining the excel-

lent precision DC characteristics. Recommended values

for CFB are between 1nF and 10nF. Additional anti-alias-

ing filtering at the output can further reduce this auto-

correction noise.

Capacitive-Load Stability

The MAX4208/MAX4209 are capable of driving capaci-

tive 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 voltage drop across the isolation resistor.

GAIN R

⎛

⎝

⎜⎞

⎠

⎟

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

14 ______________________________________________________________________________________

Power-Supply Bypass and Layout

Good layout technique optimizes performance by

decreasing the amount of stray capacitance at the

instrumentation 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 exter-

nal components as close as possible to the instrumen-

tation amplifier. Unshielded long traces at the inputs of

the instrumentation amplifier degrade the CMRR and

pick-up noise. This produces inaccurate output in high-

gain 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 current and thermo-

couple effects by thoroughly cleaning the board and

placing the matching components very close to each

other and with appropriate orientation. For best perfor-

mance, 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

recommended. 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 Amplifier

The use of indirect current-feedback architecture

makes the MAX4208/MAX4209 ideal for low-side cur-

rent-sensing 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 com-

mon-mode voltage is allowed to be at or even slightly

below ground (VSS - 0.1V).

If the currents to be measured are bidirectional, con-

nect REFIN/MODE to VDD/2 to get full dynamic range

for each direction. If the currents to be measured are

unidirectional, both REFIN/MODE and REF can be tied

to GND. However, VOL limitations can limit low-current

measurement. If currents need to be measured down to

0A, bias REFIN/MODE to a voltage above 0.2V to acti-

vate the internal buffer and to stay above amplifier VOL,

and measure both OUT and REF with a differential

input ADC.

Low-Voltage, High-Side

Current-Sense Amplifier

Power management is a critical area in high-perfor-

mance portable devices such as notebook computers.

Modern digital processors and ASICs are using smaller

transistor geometries to increase speed, reduce size,

and also lower their operating core voltages (typically

0.9V to 1.25V). The MAX4208/MAX4209 instrumentation

amplifiers can be used as a nearly zero voltage-drop,

current-sense amplifier (see Figure 5).

VCM

VCC

VCM-MAX

3/4 VCC

1/2 VCC

1/4 VCC

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

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)

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

______________________________________________________________________________________ 15

The ultra-low VOS of the MAX4208/MAX4209 allows full-

scale VSENSE of only 10mV to 20mV for minimally inva-

sive 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 1kΩand 249kΩresistors, to scale up a

lower 10mV VSENSE voltage to a larger 2.5V output volt-

age for wider dynamic range as needed.

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

Figure 5. MAX4208/MAX4209 Used as Precision Current-Sense Amplifiers for Notebook Computers with VSENSE of 20mV

IN-

IN+

REFIN/MODE

REF

MAX4208

VDD

VSS CFB

OUT

REF

G = 1 + R2

R1 BUFFER OUT =

VDD/2

Typical Application Circuit

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

16 ______________________________________________________________________________________

Chip Information

TRANSISTOR COUNT: 2335

PROCESS: BiCMOS

TOP VIEW

REFVSS

VDD

OUTIN-

IN+

REFIN/MODE

μMAX

MAX4208

MAX4209

Pin Configuration

Package Information

For the latest package outline information, go to

www.maxim-ic.com/package.

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

8 µMAX U8-1 21-0036

MAX4208/MAX4209

Ultra-Low Offset/Drift, Precision

Instrumentation Amplifiers with REF Buffer

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.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

09/07 Initial release —

14/09 Removed future products 1–5, 11, 12,