Datasheet

ManualsBrandsANALOG DEVICES ManualsLinear ICsLinear IC - In-amp InAmp MSOP 8

Micropower, Zero Drift, True Rail-to-Rail

Instrumentation Amplifier

Data Sheet

AD8237

Rev. 0

Informati

on furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700

www.analog.com

FEATURES

Gain set with 2 external resistors

Can achieve low gain drift at all gains

Ideal for battery powered instruments

Supply current: 115 µA

Rail-to-rail input and output

Zero input crossover distortion

Designed for excellent dc performance

Minimum CMRR: 106 dB

Maximum offset voltage drift: 0.3 µV/°C

Maximum gain error: 0.005% (all gains)

Maximum gain drift: 0.5 ppm/°C (all gains)

Input bias current: 1 nA guaranteed to 125°C

Bandwidth mode pin (BW) to adjust compensation

8 kV HBM ESD rating

RFI filter on-chip

Single-supply operation: 1.8 V to 5.5 V

8-lead MSOP package

APPLICATIONS

Bridge amplification

Pressure measurement

Medical instrumentation

Thermocouple interface

Portable systems

Current measurement

PIN CONFIGURATION

+IN

–IN

–V

OUT

REF

AD8237

TOP VIEW

(Not to Scale)

–

10289-001

Figure 1.

Table 1. Instrumentation Amplifiers by Category

General

Purpose

Zero

Drift

Military

Grade

Micropower

Digital

Gain

AD8421 AD8237 AD620 AD8237 AD8250

AD8221/AD8222 AD8231 AD621 AD8420 AD8251

AD8220/AD8224 AD8293 AD524 AD8235/AD8236 AD8253

AD8228 AD8553 AD526 AD627 AD8231

AD8295 AD8556 AD624

AD8226 AD8557

See www.analog.com for the latest instrumentation amplifiers.

GENERAL DESCRIPTION

The AD8237 is a micropower, zero drift, rail-to-rail input and

output instrumentation amplifier. The relative match of two

resistors sets any gain from 1 to 1000. The AD8237 has excellent

gain accuracy performance that can be preserved at any gain

with two ratio-matched resistors.

The AD8237 employs the indirect current feedback architecture to

achieve a true rail-to-rail capability. Unlike conventional in-amps,

the AD8237 can fully amplify signals with common-mode voltage

at or even slightly beyond its supplies. This enables applications

with high common-mode voltages to use smaller supplies and

save power.

The AD8237 is an excellent choice for portable systems. With a

minimum supply voltage of 1.8 V, a 115 µA typical supply current,

and wide input range, the AD8237 makes full use of a limited

power budget, yet offers bandwidth and drift performance suitable

for bench-top systems.

The AD8237 is available in an 8-lead MSOP package. Performance

is specified over the full temperature range of −40°C to +125°C.

–1

0 1 2 3 4 5

INPUT COMMON-MODE VOLTAGE (V)

OUTPUT VOLTAGE (V)

TRADITIONAL IN-AMP

(RAIL-TO-RAIL OUT)

AD8237

10289-002

G = 100

= 5V

REF

= 2.5V

Figure 2. Input Common-Mode Voltage vs. Output Voltage, +V

= 5 V, G = 100

Summary of content (28 pages)

PAGE 1
FEATURES Gain set with 2 external resistors Can achieve low gain drift at all gains Ideal for battery powered instruments Supply current: 115 µA Rail-to-rail input and output Zero input crossover distortion Designed for excellent dc performance Minimum CMRR: 106 dB Maximum offset voltage drift: 0.3 µV/°C Maximum gain error: 0.005% (all gains) Maximum gain drift: 0.
PAGE 2
AD8237 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Clock Feedthrough ..................................................................... 21 Applications ....................................................................................... 1 Input Voltage Range ................................................................... 21 Pin Configuration .............................................................
PAGE 3
Data Sheet AD8237 SPECIFICATIONS +VS = +5 V, −VS = 0 V, VREF = 2.5 V, VCM = 2.5 V, TA = 25°C, G = 1 to 1000, RL = 10 kΩ to ground, specifications referred to input, unless otherwise noted. Table 2. Parameter COMMON-MODE REJECTION RATIO (CMRR) CMRR at DC G = 1, G = 10 G = 100, G = 1000 Over Temperature (G = 1) CMRR at 1 kHz NOISE Voltage Noise Spectral Density Peak to Peak Current Noise Spectral Density Peak to Peak VOLTAGE OFFSET Offset Average Temperature Coefficient Offset RTI vs.
PAGE 4
AD8237 Parameter Settling Time 0.01% Low Bandwidth Mode G=1 G = 10 G = 100 G = 1000 High Bandwidth Mode G = 10 G = 100 G = 1000 Slew Rate Low Bandwidth Mode High Bandwidth Mode EMI Filter Frequency GAIN 2 Gain Range 3 Gain Error Gain Error vs. VCM Gain vs.
PAGE 5
Data Sheet AD8237 +VS = 1.8 V, −VS = 0 V, VREF = 0.9 V, VCM = 0.9 V, TA = 25°C, G = 1 to 1000, RL = 10 kΩ to ground, specifications referred to input, unless otherwise noted. Table 3. Parameter COMMON-MODE REJECTION RATIO (CMRR) CMRR at DC G = 1, G = 10 G = 100, G = 1000 Over Temperature (G = 1) CMRR at 1 kHz NOISE Voltage Noise Spectral Density Peak to Peak Current Noise Spectral Density Peak to Peak VOLTAGE OFFSET Offset Average Temperature Coefficient Offset RTI vs.
PAGE 6
AD8237 Parameter GAIN 2 Gain Range 3 Gain Error Gain Error vs. VCM Gain vs. Temperature Gain Nonlinearity G = 1, G = 10 G = 100 G = 1000 OUTPUT Output Swing RL = 10 kΩ to Midsupply RL = 100 kΩ to Midsupply Short-Circuit Current POWER SUPPLY Operating Range Quiescent Current Data Sheet Test Conditions/Comments G = 1 + (R2/R1) Min Typ 1 VOUT = 0.2 V to 1.6 V, G = 1 to G = 1000 Max Unit 1000 0.005 V/V % ppm/V ppm/°C 15 TA = −40°C to +125°C VOUT = 0.2 V to 1.6 V 0.
PAGE 7
Data Sheet AD8237 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 4. Parameter Supply Voltage Output Short-Circuit Current Duration Maximum Voltage at −IN, +IN, FB, or REF1 Minimum Voltage at −IN, +IN, FB, or REF1 Storage Temperature Range Junction Temperature Range ESD Human Body Model Charge Device Model Machine Model 1 Rating 6V Indefinite +VS + 0.5 V −VS − 0.5 V −65°C to +150°C −65°C to +150°C θJA is specified for a device in free air. Table 5.
PAGE 8
AD8237 Data Sheet PIN CONFIGURATION AND FUNCTION DESCRIPTIONS +IN 2 –IN 3 –VS 4 + – + – TOP VIEW (Not to Scale) 8 VOUT 7 FB 6 REF 5 +VS 10289-003 AD8237 BW 1 Figure 3. Pin Configuration Table 6. Pin Function Descriptions Pin No. 1 Mnemonic BW 2 3 4 5 6 7 8 +IN −IN −VS +VS REF FB VOUT Description For high bandwidth mode, connect this pin to +VS, or for low bandwidth mode, connect this pin to −VS. Do not leave this pin floating. Positive Input. Negative Input. Negative Supply.
PAGE 9
Data Sheet AD8237 TYPICAL PERFORMANCE CHARACTERISTICS +VS = +5 V, −VS = 0 V, VREF = 2.5 V, TA = 25°C, RL = 10 kΩ to ground, unless otherwise noted. 40 16 35 14 30 25 8 20 6 15 4 10 2 5 –60 –40 –20 0 20 40 0 10289-004 0 60 OFFSET VOLTAGE (µV) –6 –4 –2 0 2 4 6 CMRR (µV/V) Figure 4. Typical Distribution of Offset Voltage 10289-007 10 UNITS UNITS 12 Figure 7. Typical Distribution of CMRR 21 18 18 15 12 9 12 9 6 6 3 3 –0.4 –0.2 0 0.2 0.4 0.
PAGE 10
AD8237 Data Sheet 6 4 3 4 3 2 VS = 1.8V 1 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 1 0 VS = ±0.9V –1 –2 OUTPUT VOLTAGE (V) –4 –3 10289-010 0 6 5 –2 –1 0 1 2 3 Figure 13. Input Common-Mode Voltage vs. Output Voltage, G = 100, VREF = 0 V, VS = ±2.5 V and VS = ±0.9 V, RL = 5 kΩ to Ground 5.0 G = 100 VREF = 0V RL = 10kΩ VS = 5V G = 100 VREF = 0V RL = 5kΩ OUTPUT VOLTAGE (V) Figure 10. Input Common-Mode Voltage vs. Output Voltage, G = 1, VREF = 0 V, VS = 5 V and VS = 1.
PAGE 11
Data Sheet AD8237 140 15 VS = ±2.5V VCM = 0V 120 IB– 100 POSITIVE PSRR (dB) 5 0 –5 80 60 BW LIMIT 40 IB+ 20 0.5 1.0 1.5 2.0 2.5 DIFFERENTIAL INPUT VOLTAGE (V) 0 0.1 10289-016 REPRESENTATIVE SAMPLE –15 0 –2.5 –2.0 –1.5 –1.0 –0.5 140 120 100 100 NEGATIVE PSRR (dB) 120 80 60 0 0.1 20 100 1k 10k FREQUENCY (Hz) BW LIMIT GAIN = 10 GAIN = 100 GAIN = 1000 0 0.1 1 10 100 1k 10k FREQUENCY (Hz) Figure 17. Positive PSRR vs.
PAGE 12
AD8237 Data Sheet 80 70 4.5 GAIN = 1000 GAIN = 100 30 10 1k 10k 100k 1M 80 OUTPUT VOLTAGE (V p-p) GAIN (dB) GAIN = 100 GAIN = 10 10 2.5 2.0 1.5 –10 0.5 100k 1M Figure 23. Gain vs. Frequency, High Bandwidth Mode, VS = 5 V 80 MAXIMUM COMMON-MODE VOLTAGE (V p-p) GAIN = 1000 GAIN = 100 30 20 GAIN = 10 10 0 100 1k 10k 100k 1M FREQUENCY (Hz) 10289-024 –10 –20 10 1k 10k 100k FREQUENCY (Hz) 6 50 40 100 Figure 26.
PAGE 13
Data Sheet AD8237 160 BOTH BANDWIDTH MODES ONLY BW LIMIT CHANGES 140 CMRR (dB) 120 100 GAIN = 1 LOW BANDWIDTH MODE ONLY BW LIMIT 80 60 GAIN = 1 GAIN = 10 GAIN = 100 GAIN = 1000 0 0.1 1 0.4µV/DIV 10 100 1k 10k 100k FREQUENCY (Hz) Figure 31. 0.1 Hz to 10 Hz RTI Voltage Noise Figure 28. CMRR vs.
PAGE 14
AD8237 Data Sheet 0.010 20 VIN = ±500mV G = 100 0.008 15 0.006 NONLINEARITY (ppm) 10 GAIN ERROR (%) 0.004 0.002 0 –0.002 –0.004 5 0 –5 –10 –0.006 –2.0 –1.5 –1.0 –0.5 0 0.5 1.0 1.5 2.0 2.5 COMMON-MODE VOLTAGE (V) –20 10289-034 –0.010 –2.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Figure 34. Gain Error vs. Common-Mode Voltage, G = 1 5.0 Figure 37.
PAGE 15
Data Sheet AD8237 Figure 40. Large Signal Pulse Response, Low Bandwidth Mode, G = 10, RL = 10 kΩ, CL = 10 pF Figure 43. Large Signal Pulse Response, High Bandwidth Mode, G = 10, RL = 10 kΩ, CL = 10 pF G = 100 LOW BANDWIDTH MODE 400µs/DIV G = 100 HIGH BANDWIDTH MODE 10289-043 1V/DIV 1V/DIV G = 1000 HIGH BANDWIDTH MODE G = 1000 LOW BANDWIDTH MODE 1V/DIV 10289-044 2ms/DIV 400µs/DIV Figure 44. Large Signal Pulse Response, High Bandwidth Mode, G = 100, RL = 10 kΩ, CL = 10 pF Figure 41.
PAGE 16
AD8237 Data Sheet G=1 LOW BANDWIDTH MODE 20mV/DIV Figure 46. Small Signal Pulse Response, G = 1, RL = 10 kΩ, CL = 100 pF, Low Bandwidth Mode 2ms/DIV 10289-051 10µs/DIV 10289-048 20mV/DIV G = 1000 LOW BANDWIDTH MODE Figure 49. Small Signal Pulse Response, G = 1000, RL = 10 kΩ, CL = 100 pF, Low Bandwidth Mode G=1 LOW BANDWIDTH MODE G = 10 LOW BANDWIDTH MODE NO LOAD 100pF 560pF 1nF 20mV/DIV Figure 47. Small Signal Pulse Response, G = 10, RL = 10 kΩ, CL = 100 pF, Low Bandwidth Mode Figure 50.
PAGE 17
Data Sheet AD8237 80 G = 100 HIGH BANDWIDTH MODE NORMALIZED TO 25°C VS = ±2.5V OFFSET VOLTAGE (µV) 60 100µs/DIV 20 0 –20 –40 –60 –80 –40 –25 –10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) Figure 52. Small Signal Pulse Response, G = 100, RL = 10 kΩ, CL = 100 pF, High Bandwidth Mode 10289-057 20mV/DIV 10289-054 fCHOP 40 Figure 55. Offset Voltage vs. Temperature 50 G = 1000 HIGH BANDWIDTH MODE NORMALIZED TO 25°C GAIN = 1 VS = ±2.
PAGE 18
AD8237 Data Sheet +VS REPRESENTATIVE SAMPLE 400 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES –0.2 300 200 –IN BIAS CURRENT 100 +IN BIAS CURRENT 0 –100 –200 INPUT OFFSET CURRENT –300 –400 –10 5 20 35 50 65 80 95 110 125 +0.4 –VS 1k 500 10k 100k 1M LOAD RESISTANCE (Ω) Figure 61. Output Voltage Swing vs. Load Resistance, VS = ±2.5 V Figure 58. Input Bias Current and Input Offset Current vs. Temperature +VS REPRESENTATIVE SAMPLE –0.
PAGE 19
Data Sheet AD8237 200 180 VS = 5V 140 120 100 VS = 1.8V 80 60 40 20 0 –40 –25 –10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) 10289-066 SUPPLY CURRENT (µA) 160 Figure 64. Supply Current vs. Temperature, VS = 5 V, VS = 1.8 V Rev.
PAGE 20
AD8237 Data Sheet THEORY OF OPERATION INTERNAL IN-AMP AD8237 + VOUT TIA – I1 – I2 +VS RFI FILTER +IN –VS +VS ALS RFI FILTER –IN V VCM = S 2 FB –IN – + gm1 TO gm1 – + I2 I1 + – V VCM = S 2 gm2 + – FB –VS +VS ALS REF –VS –VS R1 + RFI FILTER TO gm2 R2 – RFI FILTER 10289-067 +VS Figure 65.
PAGE 21
Data Sheet AD8237 The bias current at the FB pin is dependent on the common-mode and differential input impedance. FB bias current errors from the common-mode input impedance can be reduced by placing a resistor value of R1||R2 in series with the REF terminal, as shown in Figure 66. At higher gains, this resistor can simply be the same value as R1.
PAGE 22
AD8237 Data Sheet INPUT PROTECTION USING THE REFERENCE PIN If no external protection is used, keep the inputs of the AD8237 within the voltages specified in the absolute maximum ratings. If the application requires voltages beyond these ratings, input protection resistors can be placed in series with the inputs of the AD8237 to limit the current to 5 mA. For example, if +VS is 3 V and a 10 V overload voltage can occur at the inputs, place a protection resistor of at least (10 V − 3 V)/5 mA = 1.
PAGE 23
Data Sheet AD8237 Resistance at the reference pin does affect the gain of the AD8237; however, if this resistance is constant, the gain setting resistors can be adjusted to compensate. For example, the AD8237 can be driven with a voltage divider, as shown in Figure 72. +IN FB REF VS R1 R2 R2 + R3||R4 R4 R1 10289-074 R3 G=1+ Use a stable dc voltage to power the instrumentation amplifier. Noise on the supply pins can adversely affect performance.
PAGE 24
AD8237 Data Sheet CORRECT INCORRECT +VS +VS VOUT VOUT AD8237 AD8237 –VS –VS TRANSFORMER TRANSFORMER +VS +VS VOUT VOUT AD8237 AD8237 10MΩ –VS –VS THERMOCOUPLE THERMOCOUPLE +VS +VS C C VOUT AD8237 1 R fHIGH-PASS = 2πRC VOUT AD8237 C C –VS –VS CAPACITIVELY COUPLED CAPACITIVELY COUPLED Figure 74. Creating an IBIAS Path Rev.
PAGE 25
Data Sheet AD8237 APPLICATIONS INFORMATION BATTERY CURRENT MONITOR PROGRAMMABLE GAIN IN-AMP The micropower current consumption, unique topology, and rail-torail input of the AD8237 make it ideal for battery-powered current sensing applications. When configured as shown in Figure 75, the AD8237 is able to obtain an accurate high-side current measurement for both charging and discharging. Depending on the nature of the load, +VS may require RC decoupling.
PAGE 26
AD8237 Data Sheet AD8237 IN AN ECG FRONT END With this system architecture, large gains can be applied at the in-amp stage, and the requirements of the rest of the system can be greatly reduced. This also reduces noise and offset error contributions from devices after the in-amp in the signal path. The circuit in Figure 77 illustrates the core concept. Additional op amps can be added for improved performance, such as input buffering, filtering, and driven lead, if it is required by the system.
PAGE 27
Data Sheet AD8237 OUTLINE DIMENSIONS 3.20 3.00 2.80 8 3.20 3.00 2.80 1 5 5.15 4.90 4.65 4 PIN 1 0.65 BSC 0.95 0.85 0.75 1.10 MAX 0.15 0.00 0.38 0.22 COPLANARITY 0.10 0.23 0.08 8° 0° 0.80 0.60 0.40 SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 78.