offset voltage: Input offset drift: 0.005 V/°C Rail-to-rail input outp
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Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers AD8571/AD8572/AD8574
offset voltage: Input offset drift: 0.005 V/°C Rail-to-rail input output swing V/2.7 single-supply operation High gain, CMRR, PSRR: Ultralow input bias current: supply current: A/op Overload recovery time: external capacitors required
CONFIGURATIONS
01104-001
AD8571
VIEW (Not Scale)
AD8571
CONNECT
CONNECT
Figure 8-Lead MSOP Suffix)
Figure 8-Lead SOIC Suffix)
01104-002
01104-005
APPLICATIONS
Temperature sensors Pressure sensors Precision current sensing Strain gage amplifiers Medical instrumentation Thermocouple amplifiers
AD8572
VIEW (Not Scale)
AD8572
VIEW (Not Scale)
Figure 8-Lead TSSOP Suffix)
Figure 8-Lead SOIC Suffix)
01104-003
GENERAL DESCRIPTION
This family amplifiers ultralow offset, drift, bias current. AD8571, AD8572, AD8574 single, dual, quad amplifiers, respectively, featuring rail-to-rail input output swings. guaranteed operate from single supply. AD857x family provides benefits previously found only expensive auto-zeroing chopper-stabilized amplifiers. Using Analog Devices, Inc. topology, these zero-drift amplifiers combine cost with high accuracy. external capacitors required.) Using patented spread-spectrum auto-zero technique, AD857x family eliminates intermodulation effects from interaction chopping function with signal frequency applications. With offset voltage only drift 0.005 V/°C, AD857x family perfectly suited applications where error sources cannot tolerated. Position pressure sensors, medical equipment, strain gage amplifiers benefit greatly from nearly zero drift over their operating temperature range. Many more systems require rail-to-rail input output swings provided AD857x family.
AD8574
AD8574
VIEW (Not Scale)
VIEW (Not Scale)
01104-006
Figure 14-Lead TSSOP Suffix)
Figure 14-Lead SOIC Suffix)
AD857x family specified extended industrial/ automotive (-40°C +125°C) temperature range. AD8571 single amplifier available 8-lead MSOP narrow 8-lead SOIC packages. AD8572 dual amplifier available 8-lead narrow SOIC 8-lead TSSOP surface mount packages. AD8574 quad amplifier available narrow 14-lead SOIC 14-lead TSSOP packages.
Rev.
Information furnished Analog Devices believed accurate reliable. However, responsibility assumed Analog Devices use, infringements patents other rights third parties that result from use. Specifications subject change without notice. license granted implication otherwise under patent patent rights Analog Devices. Trademarks registered trademarks property their respective owners.
Technology Way, P.O. 9106, Norwood, 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2006 Analog Devices, Inc. rights reserved.
01104-004
VIEW (Not Scale)
AD8571/AD8572/AD8574 TABLE CONTENTS
Features Applications. General Description Configurations Revision History Specifications. Electrical Characteristics. Electrical Characteristics. Absolute Maximum Ratings. Thermal Characteristics Caution. Typical Performance Characteristics Functional Description Amplifier Architecture Basic Auto-Zero Amplifier Theory. Auto-Zero Phase. Amplification Phase High Gain, CMRR, PSRR. Maximizing Performance Through Proper Layout Noise Characteristics Random Auto-Zero Correction Eliminates Intermodulation Distortion Broadband External Resistor Noise Considerations. Output Overdrive Recovery. Input Overvoltage Protection Output Phase Reversal. Capacitive Load Drive Power-Up Behavior Applications. Precision Strain Gage Circuit Instrumentation Amplifier High Accuracy Thermocouple Amplifier Precision Current Meter. Precision Voltage Comparator. Outline Dimensions Ordering Guide
REVISION HISTORY
09/06-Rev. Rev. Updated Format.Universal Renumbered Figures .Universal Changes Figure Changes Figure Changes Figure Updated Outline Dimensions Changes Ordering Guide 07/03-Rev. Rev. Renumbered Figures .Universal Changes Ordering Guide Change Figure Updated Outline Dimensions.
10/99-Revision Initial Version
Rev. Page
AD8571/AD8572/AD8574 SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
25°C, unless otherwise noted. Table
Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Input Offset Current Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Offset Voltage Drift OUTPUT CHARACTERISTICS Output Voltage High Symbol -40°C +125°C -40°C +125°C -40°C +125°C CMRR VOS/T -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C Output Current POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier DYNAMIC PERFORMANCE Slew Rate Overload Recovery Time Gain Bandwidth Product NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density
Conditions
Unit V/°C nV/Hz fA/Hz
0.005 4.998 4.997 4.98 4.975 1000 0.05 0.41
0.04
4.99 4.99 4.95 4.95
Output Voltage
Short-Circuit Limit
-40°C +125°C PSRR -40°C +125°C -40°C +125°C
1075
Gain testing dependent upon test bandwidth.
Rev. Page
AD8571/AD8572/AD8574
ELECTRICAL CHARACTERISTICS
1.35 1.35 25°C, unless otherwise noted. Table
Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Input Offset Current Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Offset Voltage Drift OUTPUT CHARACTERISTICS Output Voltage High Symbol -40°C +125°C -40°C +125°C -40°C +125°C CMRR VOS/T -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C Output Current POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier DYNAMIC PERFORMANCE Slew Rate Overload Recovery Time Gain Bandwidth Product NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density
Conditions
Unit V/°C nV/Hz fA/Hz
0.005 2.697 2.696 2.68 2.675 0.05
0.04
2.685 2.685 2.67 2.67
Output Voltage
Short-Circuit Limit
-40°C +125°C PSRR -40°C +125°C -40°C +125°C
1000
Gain testing dependent upon test bandwidth.
Rev. Page
AD8571/AD8572/AD8574 ABSOLUTE MAXIMUM RATINGS
Table
Parameter Supply Voltage Input Voltage Differential Input Voltage1 (Human Body Model) Output Short-Circuit Duration Storage Temperature Range Packages Operating Temperature Range AD8571A/AD8572A/AD8574A Junction Temperature Range Packages Lead Temperature Range (Soldering, sec)
THERMAL CHARACTERISTICS
Rating ±5.0 2000 Indefinite -65°C +150°C -40°C +125°C -65°C +150°C 300°C
specified worst-case conditions, that specified device soldered circuit board SOIC TSSOP packages. Table Thermal Resistance
Package Type 8-Lead MSOP (RM) 8-Lead TSSOP (RU) 8-Lead SOIC 14-Lead TSSOP (RU) 14-Lead SOIC Unit °C/W °C/W °C/W °C/W °C/W
Differential input voltage limited ±5.0 supply voltage, whichever less.
CAUTION
Stresses above those listed under Absolute Maximum Ratings cause permanent damage device. This stress rating only; functional operation device these other conditions above those indicated operational section this specification implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
Rev. Page
AD8571/AD8572/AD8574 TYPICAL PERFORMANCE CHARACTERISTICS
2.7V 1.35V 25°C
2.5V 25°C
NUMBER AMPLIFIERS
NUMBER AMPLIFIERS
01104-007
-1.5
-0.5
-1.5
-0.5
OFFSET VOLTAGE (µV)
OFFSET VOLTAGE (µV)
Figure Input Offset Voltage Distribution
INPUT BIAS CURRENT (pA)
Figure Input Offset Voltage Distribution
-40°C, +25°C, +85°C
NUMBER AMPLIFIERS
+85°C +25°C -40°C
01104-008
2.5V -40°C +125°C
INPUT COMMON-MODE VOLTAGE
INPUT OFFSET DRIFT (nV/°C)
Figure Input Bias Current Common-Mode Voltage
1500 1000
Figure Input Offset Voltage Drift Distribution
125°C
25°C
INPUT BIAS CURRENT (pA)
OUTPUT VOLTAGE (mV)
SOURCE SINK
-500 -1000 -1500 -2000
01104-009
0.001
0.01
COMMON-MODE VOLTAGE
LOAD CURRENT (mA)
Figure Input Bias Current Common-Mode Voltage
Figure Output Voltage Supply Rail Output Current
Rev. Page
01104-012
0.0001
01104-011
01104-010
-2.5
-2.5
AD8571/AD8572/AD8574
SUPPLY CURRENT AMPLIFIER (µA)
2.7V 25°C
25°C
OUTPUT VOLTAGE (mV)
SOURCE SINK
01104-013
0.001
0.01
LOAD CURRENT (mA)
SUPPLY VOLTAGE
Figure Output Voltage Supply Rail Output Current
Figure Supply Current Supply Voltage
1000 2.5V
2.7V
INPUT BIAS CURRENT (pA)
01104-014
100k
FREQUENCY (Hz)
100M
TEMPERATURE (°C)
Figure Bias Current Temperature
Figure Open-Loop Gain Phase Shift Frequency
SUPPLY CURRENT (mA)
2.7V
01104-015
100k
FREQUENCY (Hz)
100M
TEMPERATURE (°C)
Figure Supply Current Temperature
Figure Open-Loop Gain Phase Shift Frequency
Rev. Page
01104-018
PHASE SHIFT (Degrees)
OPEN-LOOP GAIN (dB)
01104-017
PHASE SHIFT (Degrees)
OPEN-LOOP GAIN (dB)
01104-016
0.0001
AD8571/AD8572/AD8574
CLOSED-LOOP GAIN (dB)
2.7V
OUTPUT IMPEDANCE
01104-019
-100
100k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure Closed-Loop Gain Frequency
Figure Output Impedance Frequency
-100
2.7V 300pF
CLOSED-LOOP GAIN (dB)
100k
01104-020
500mV
FREQUENCY (Hz)
Figure Closed-Loop Gain Frequency
OUTPUT IMPEDANCE
Figure Large Signal Transient Response
2.7V
300pF
100k
01104-021
FREQUENCY (Hz)
Figure Output Impedance Frequency
Figure Large Signal Transient Response
Rev. Page
01104-024
01104-023
01104-022
AD8571/AD8572/AD8574
SMALL SIGNAL OVERSHOOT
±1.35V 50pF
±2.5V 25°C
01104-028
50mV
01104-025
CAPACITANCE (pF)
Figure Small Signal Transient Response
Figure Small Signal Overshoot Load Capacitance
±2.5V 50pF
±2.5V -200mV (RET GND) -100
VOUT
01104-026
20µs BOTTOM SCALE: 1V/DIV SCALE: 200mV/DIV
01104-029
50mV
Figure Small Signal Transient Response
±1.35V 25°C
Figure Positive Overvoltage Recovery
±2.5V 200mV (RET GND) -100
SMALL SIGNAL OVERSHOOT
VOUT 20µs
01104-027
01104-030
CAPACITANCE (pF)
BOTTOM SCALE: 1V/DIV SCALE: 200mV/DIV
Figure Small Signal Overshoot Load Capacitance
Figure Negative Overvoltage Recovery
Rev. Page
AD8571/AD8572/AD8574
±2.5V -100 60mV
±1.35V
PSRR (dB)
-PSRR +PSRR
200µs
01104-031
100k
FREQUENCY (Hz)
Figure Phase Reversal
2.7V
CMRR (dB)
Figure PSRR Frequency ±1.35
±2.5V
PSRR (dB)
+PSRR
-PSRR
100k
01104-032
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure CMRR Frequency
Figure PSRR Frequency ±2.5
OUTPUT SWING p-p)
CMRR (dB)
±1.35V 25°C
FREQUENCY (Hz)
FREQUENCY (Hz)
100k
Figure CMRR Frequency
Figure Maximum Output Swing Frequency
Rev. Page
01104-036
100k
01104-033
01104-035
01104-034
AD8571/AD8572/AD8574
±2.5V 25°C
2.7V
OUTPUT SWING p-p)
FREQUENCY (Hz)
100k
01104-037
FREQUENCY (kHz)
Figure Maximum Output Swing Frequency
Figure Voltage Noise Density from
±1.35V 120,000
01104-038
2.7V
(nV/
50mV
FREQUENCY (kHz)
Figure Noise
Figure Voltage Noise Density from
±2.5V 120,000
01104-039
(nV/
50mV
FREQUENCY (kHz)
Figure Noise
Figure Voltage Noise Density from
Rev. Page
01104-042
01104-041
01104-040
(nV/
AD8571/AD8572/AD8574
2.7V 5.5V
POWER SUPPLY REJECTION (dB)
(nV/
FREQUENCY (kHz)
TEMPERATURE (°C)
Figure Voltage Noise Density from
Figure Power Supply Rejection Temperature
SHORT-CIRCUIT CURRENT (mA)
2.7V ISC-
(nV/
ISC+
FREQUENCY (kHz)
TEMPERATURE (°C)
Figure Voltage Noise Density from
Figure Output Short-Circuit Current Temperature
Rev. Page
01104-046
01104-044
01104-045
01104-043
AD8571/AD8572/AD8574
SHORT-CIRCUIT CURRENT (mA)
OUTPUT VOLTAGE SWING (mV)
ISC-
ISC+
100k
01104-047
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure Output Short-Circuit Current Temperature
OUTPUT VOLTAGE SWING (mV) 100k
Figure Output Voltage Supply Rail Temperature
TEMPERATURE (°C)
Figure Output Voltage Supply Rail Temperature
Rev. Page
01104-048
01104-049
-100
AD8571/AD8572/AD8574 FUNCTIONAL DESCRIPTION
AD8571/AD8572/AD8574 CMOS amplifiers that achieve their high degree precision through random frequency auto-zero stabilization. autocorrection topology allows AD857x maintain offset voltage over wide temperature range, randomized auto-zero clock eliminates intermodulation distortion (IMD) errors amplifier output. AD857x from single-supply voltage extremely offset voltage products allows amplifier easily configured high gains without risk excessive output voltage errors. This makes AD857x ideal amplifier applications requiring both precision distortion signals. extremely small temperature drift nV/°C ensures minimum offset voltage error over entire temperature range -40°C +125°C. These combined features make AD857x excellent choice variety sensitive measurement automotive applications.
BASIC AUTO-ZERO AMPLIFIER THEORY
Autocorrection amplifiers technology. Various implementations have been available more than years some improvements have been made over time. AD857x design offers number significant performance improvements over older versions while attaining very substantial reduction device cost. This section offers simplified explanation AD857x able offer extremely offset voltages high open-loop gains. noted Amplifier Architecture section, each AD857x contains internal amplifiers. used primary amplifier, other autocorrection, nulling, amplifier. Each amplifier associated input offset voltage that modeled voltage source series with noninverting input. Figure Figure these labeled VOSX, where denotes amplifier associated with offset: nulling amplifier, primary amplifier. open-loop gain inputs each amplifier given Both amplifiers also have third voltage input with associated open-loop gain There modes operation determined action sets switches amplifier: auto-zero phase amplification phase.
AMPLIFIER ARCHITECTURE
Each AD857x consists amplifiers: main amplifier secondary amplifier that used correct offset voltage main amplifier. Both consist rail-to-rail input stage, allowing input common-mode voltage range reach both supply rails. input stage consists NMOS differential pair operating concurrently with parallel PMOS differential pair. outputs from differential input stages combined another gain stage whose output used drive rail-to-rail output stage. wide voltage swing amplifier achieved using output transistors common-source configuration. output voltage range limited drain-to-source resistance these transistors. amplifier required source sink more output current, voltage drop across these transistors increases their resistance (rds). Simply put, output voltage does swing close rail under heavy output current conditions does with light output current. This characteristic rail-to-rail output amplifiers. Figure Figure show close output voltage rails with given output current. output AD857x shortcircuit protected approximately current. AD857x amplifiers have exceptional gain, yielding greater than open-loop gain with load Because output transistors configured common-source configuration, gain output stage, thus open-loop gain amplifier, dependent load resistance. Open-loop gain decreases with smaller load resistances. This another characteristic rail-to-rail output amplifiers.
AUTO-ZERO PHASE
this phase, switches closed switches opened. Here, nulling amplifier taken gain loop shorting inputs together. course, there degree offset voltage, shown VOSA, inherent nulling amplifier that maintains potential difference between inputs. nulling amplifier feedback loop closed through VOSA appears output nulling CM1, internal capacitor AD857x. Mathematically, express this time domain
VOSA
this also expressed
AVOSA
This shows that offset voltage nulling amplifier times gain factor appears output nulling amplifier thus capacitor.
Rev. Page
AD8571/AD8572/AD8574
VIN+ VIN- VOSA VOSB VOUT
long-term wear time, both which much slower than auto-zero clock frequency AD857x. This effectively makes time invariant, Equation rewritten
AAVIN
)VOSA BAVOSA
01104-050
Figure Auto-Zero Phase Amplifier
VOSA
AMPLIFICATION PHASE
When switches close switches open amplification phase, this offset voltage remains essentially corrects error from nulling amplifier. voltage across designated VNA. potential difference between inputs primary amplifier designated VIN, (VIN+ VIN-). output nulling amplifier then expressed
VOSA
VIN+ VIN- VOSA VOSB VOUT
Here, auto-zeroing becomes apparent. Note that term reduced factor. This shows nulling amplifier greatly reduced offset voltage error even before correcting primary amplifier. Thus, primary amplifier output voltage voltage output AD857x amplifier. equal
VOUT VOSB
amplification phase, VNB, this rewritten
VOUT ABVIN ABVOSB
combining terms yields
01104-051
VOUT
BVOSA
BVOSB
(10)
Figure Output Phase Amplifier
Because open there place discharge, voltage (VNA) present time equal voltage output nulling (VOA) time when closed. period autocorrection switching frequency designated then amplifier switches between phases every Therefore, amplification phase
AD857x architecture optimized such that addition, gain product AABB much greater than Thus, Equation simplified
VOUT (VOSA VOSB
(11)
Most obvious gain product both primary nulling amplifiers. This AABA term what gives AD857x extremely high open-loop gain. understand VOSA VOSB relate overall effective input offset voltage complete amplifier, generic amplifier equation
VOUT (VIN
(12)
substituting Equation Equation into Equation yields
AVOSA AVIN AVOSA sake simplification, assumed that autocorrection frequency much faster than potential change VOSA VOSB. This good assumption since changes offset voltage function temperature variation
where open-loop gain amplifier VOS, effective offset voltage. Putting Equation into form Equation gives
VOUT VOS,
Therefore
VOSA VOSB
(13)
(14)
Rev. Page
AD8571/AD8572/AD8574
Thus, offset voltages both primary nulling amplifiers reduced Gain Factor This takes typical input offset voltage from several millivolts down effective input offset voltage submicrovolts. This autocorrection scheme makes AD857x family amplifiers extremely precise.
VIN1 VIN2 GUARD RING GUARD RING
01104-053
AD8572
VREF VREF
HIGH GAIN, CMRR, PSRR
Common-mode power supply rejection indications amount offset voltage amplifier result change input common-mode power supply voltages. shown Amplification Phase section, autocorrection architecture AD857x allows effectively minimize offset voltages. technique also corrects offset errors caused common-mode voltage swings power supply variations. This results superb CMRR PSRR figures excess Because autocorrection occurs continuously, these figures maintained across entire temperature range device, from -40°C +125°C.
Figure View AD8572 SOIC Layout with Guard Rings
Other potential sources offset error thermoelectric voltages circuit board. This voltage, also called Seebeck voltage, occurs junction dissimilar metals proportional temperature junction. most common metallic junctions circuit board solder-toboard trace solder-to-component lead. Figure shows cross-section view thermal voltage error sources. When temperature board component (TA1) differs from temperature other (TA2), Seebeck voltages equal, resulting thermal voltage error. This thermocouple error reduced using dummy components match thermoelectric error source. Placing dummy component close possible partner ensures both Seebeck voltages equal, thus canceling thermocouple error. Maintaining constant ambient temperature circuit board further reduces this error. ground plane helps distribute heat throughout board also reduces noise pickup.
COMPONENT LEAD VSC1 VTS1 BOARD COPPER TRACE TA2, THEN VTS1 VSC1 VTS2 VSC2 VSC2 SOLDER VTS2
MAXIMIZING PERFORMANCE THROUGH PROPER LAYOUT
achieve maximum performance extremely high input impedance offset voltage AD857x, care should taken circuit board layout. board surface must remain clean free moisture avoid leakage currents between adjacent traces. Surface coating circuit board reduces surface moisture provides humidity barrier, reducing parasitic resistance board. guard rings around amplifier inputs further reduces leakage currents. Figure shows guard ring should configured Figure shows view surface mount layout arranged. guard ring does need specific width, should form continuous loop around both inputs. setting guard ring voltage equal voltage noninverting input, parasitic capacitance minimized well. further reduction leakage currents, components mounted board using Teflon® standoff insulators.
SURFACE MOUNT COMPONENT
Figure Mismatch Seebeck Voltages Causes Thermoelectric Voltage Error
VOUT
AD8572
VOUT
AD8572
01104-052
AD8572
/R1)
Figure Guard Ring Layout Connections Reduce Board Leakage Currents
Figure Using Dummy Components Cancel Thermoelectric Voltage Errors
Rev. Page
01104-055
VOUT
VOUT
AD8571/AD8572/ AD8574
01104-054
AD8571/AD8572/AD8574
NOISE CHARACTERISTICS
Another advantage auto-zero amplifiers their ability cancel flicker noise. Flicker noise, also known noise, noise inherent physics semiconductor devices increases every octave decrease frequency. corner frequency amplifier frequency which flicker noise equal broadband noise amplifier. lower frequencies, flicker noise dominates, causing higher degrees error sub-Hertz frequencies precision applications. Because AD857x amplifiers self-correcting amps, they have increasing flicker noise lower frequencies. essence, frequency noise treated slowly varying offset error greatly reduced result autocorrection. correction becomes more effective noise frequency approaches offsetting tendency noise increase exponentially frequency decreases. This allows AD857x have lower noise near than standard noise amplifiers that susceptible noise.
60dB
OUTPUT SIGNAL
-100
01104-057
-120
FREQUENCY (kHz)
Figure Spectral Analysis AD857x Output with Gain
Figure shows spectral output AD8572 configured high gain with input signal applied. Note absence products spectrum. signal-tonoise (SNR) ratio output signal better than 0.1%.
60dB
RANDOM AUTO-ZERO CORRECTION ELIMINATES INTERMODULATION DISTORTION
AD857x used conventional gains MHz. auto-zero correction frequency device continuously varies, based pseudorandom generator with uniform distribution from kHz. randomization autocorrection clock creates continuous randomization intermodulation distortion (IMD) products that show simple broadband noise output amplifier. This noise naturally combines with amplifier voltage noise root-squared-sum fashion, resulting output free IMD. Figure shows spectral output AD8572 with amplifier configured unity gain input grounded. Figure shows spectral output with amplifier configured gain
-100
01104-058
-120
FREQUENCY (kHz)
Figure Spectral Analysis AD857x High Gain with Input Signal
OUTPUT SIGNAL
-100 -120
01104-056
-140 -160
FREQUENCY (kHz)
Figure Spectral Analysis AD857x Output Unity Gain Configuration
Rev. Page
AD8571/AD8572/AD8574 BROADBAND EXTERNAL RESISTOR NOISE CONSIDERATIONS
total broadband noise output from amplifier primarily function three types noise: input voltage noise from amplifier, input current noise from amplifier, Johnson noise from external resistors used around amplifier. Input voltage noise, strictly function amplifier used. Johnson noise from resistor function resistance temperature. Input current noise, creates equivalent voltage noise proportional resistors used around amplifier. These noise sources correlated with each other their combined noise sums rootsquared-sum fashion. full equation given amplifier high gain configuration with input signal that forces output voltage supply rail. input voltage then stepped down linear region amplifier, usually halfway between supplies. time from input signal step-down output settling within final value overdrive recovery time. Many competitors' autocorrection amplifiers require number auto-zero clock cycles recover from output overdrive some take several milliseconds output settle properly.
INPUT OVERVOLTAGE PROTECTION
Although AD857x rail-to-rail input amplifier, care should taken ensure that potential difference between inputs does exceed Under normal operating conditions, amplifier corrects output ensure inputs same voltage. However, device configured comparator, under some unusual operating condition, input voltages forced different potentials. This could cause excessive current flow through internal diodes AD857x used protect input stage against overvoltage. either input exceeds either supply rail more than large amounts current begin flow through protection diodes amplifier. These diodes connected between inputs each supply rail protect input transistors against electrostatic discharge event normally reverse-biased. However, input voltage exceeds supply voltage, these diodes become forward-biased. Without current-limiting, excessive amounts current flow through these diodes causing permanent damage device. inputs subject overvoltage, appropriate series resistors should inserted limit diode current less than
n,TOTAL 4kTrs
(15)
where: input voltage noise amplifier. input current noise amplifier. source resistance connected noninverting terminal. Boltzmann's constant (1.38 10-23 J/K). ambient temperature Kelvin 273.15 °C). input voltage noise density, AD857x nV/Hz, input noise, fA/Hz. TOTAL dominated input voltage noise provided source resistance less than With source resistance greater than overall noise system dominated Johnson noise resistor itself. Because input current noise AD857x very small, does become dominant term unless greater than which impractical value source resistance. total noise, TOTAL, expressed volts-per-square-root Hertz, equivalent noise over certain bandwidth found
n,TOTAL
where bandwidth interest Hertz.
(16)
OUTPUT PHASE REVERSAL
Output phase reversal occurs some amplifiers when input common-mode voltage range exceeded. common-mode voltage moved outside common-mode range, outputs these amplifiers suddenly jump opposite direction supply rail. This result differential input pair shutting down, causing radical shifting internal voltages that results erratic output behavior. AD857x amplifier been carefully designed prevent output phase reversal, provided both inputs maintained within supply voltages. both inputs could exceed either supply voltage, resistor should placed series with input limit current less than ensure output does reverse phase.
OUTPUT OVERDRIVE RECOVERY
AD857x amplifiers have excellent overdrive recovery only from either supply rail. This characteristic particularly difficult autocorrection amplifiers, because nulling amplifier requires substantial amount time error correct main amplifier back valid output. Figure Figure show positive negative overdrive recovery time AD857x. output overdrive recovery autocorrection amplifier defined time takes output correct final voltage from overload state. measured placing
Rev. Page
AD8571/AD8572/AD8574
CAPACITIVE LOAD DRIVE
AD857x excellent capacitive load driving capabilities safely drive from single supply. Although device stable, capacitive loading limits bandwidth amplifier. Capacitive loads also increase amount overshoot ringing output. snubber network, shown Figure used compensate amplifier against capacitive load ringing overshoot.
Table Snubber Network Values Driving Capacitive Loads
CLOAD 0.47
POWER-UP BEHAVIOR
power-up, AD857x settles valid output within Figure shows oscilloscope photo output amplifier along with power supply voltage, Figure shows test circuit. With amplifier configured unity gain, device takes approximately settle final output voltage, hundreds microseconds faster than many other autocorrection amplifiers.
200mV
AD8571/ AD8572/ AD8574
0.47µF 4.7nF
VOUT
Figure Snubber Network Configuration Driving Capacitive Loads
Although snubber does recover loss amplifier bandwidth from load capacitance, does allow amplifier drive larger values capacitance while maintaining minimum overshoot ringing. Figure shows output AD857x driving capacitor with without snubber network.
WITH SNUBBER
01104-059
VOUT
BOTTOM TRACE 2V/DIV TRACE 1V/DIV
01104-061
Figure AD857x Output Behavior Power-Up
WITHOUT SNUBBER
100k
CLOAD 4.7nF 100mV
01104-060
optimum value resistor capacitor function load capacitance best determined empirically since actual CLOAD includes stray capacitances differ substantially from nominal capacitive load. Table shows some snubber network values that used starting points.
Figure AD857x Test Circuit Turn-On Time
Rev. Page
01104-062
Figure Overshoot Ringing Substantially Reduced Using Snubber Network
100k
AD8571/ AD8572/ AD8574
VOUT
AD8571/AD8572/AD8574 APPLICATIONS
PRECISION STRAIN GAGE CIRCUIT
extremely offset voltage AD8572 makes ideal amplifier application requiring accuracy with high gains, such weigh scale strain gage. Figure shows configuration single supply, precision strain gage measurement system. REF192 provides precision reference voltage amplifier boosts this voltage provide reference strain gage resistor bridge. provides current drive bridge network. used amplify output bridge with full-scale output voltage equal
ideal difference amplifier, ratio resistors exactly equal
(19)
setting output voltage system
VOUT
(20)
(17)
finite component tolerance, ratio between four resistors exactly equal, mismatch results reduction common-mode rejection from system. Referring Figure exact common-mode rejection ratio expressed
where resistance load cell. Using values given Figure output voltage linearly varies from with strain under full strain.
2N2222 EQUIVALENT 4.0V 2.5V
CMRR
R1R4 2R2R4 R2R3 2R1R4 2R2R3
(21)
REF192
AD8572-B
three-op instrumentation amplifier configuration shown Figure output difference amplifier unity gain with four resistors equal value. tolerance resistors used circuit given worst-case CMRR instrumentation amplifier
CMRRMIN
17.4k
(22)
LOAD CELL
40mV FULL-SCALE
AD8572-A
VOUT
AD8574-A
01104-063
17.4k NOTE: 0.1% TOLERANCE RESISTORS.
VOUT
Figure Precision Strain Gage Amplifier
AD8574-C
INSTRUMENTATION AMPLIFIER
high common-mode rejection, high open-loop gain, operation down supply voltage make AD857x excellent choice discrete single-supply instrumentation amplifiers. common-mode rejection ratio AD857x greater than CMRR system also function external resistor tolerances. gain difference amplifier shown Figure given
VOUT
AD8574-B
VOUT
RTRIM
01104-065
Figure Discrete Instrumentation Amplifier Configuration
(18)
Thus, using tolerance resistors results worst-case system CMRR 0.02, Therefore, either high precision resistors additional trimming resistor, shown Figure should used achieve high common-mode rejection. value this trimming resistor should equal value multiplied tolerance. example, using resistors with tolerance would require series trimming resistor equal
AD8571/ AD8572/ AD8574
VOUT
HIGH ACCURACY THERMOCOUPLE AMPLIFIER
Figure shows K-type thermocouple amplifier configuration with cold junction compensation. Even from supply, AD8571 provide enough accuracy achieve resolution better than 0.02°C from 500°C. used temperature measuring device correct cold-junction error from
Rev. Page
THEN VOUT
Figure Using AD857x Difference Amplifier
01104-064
AD8571/AD8572/AD8574
thermocouple should placed close possible terminating junctions. With thermocouple measuring immersed bath, should adjusted until output Using values shown Figure output voltage tracks temperature mV/°C. wider range temperature measurement, decreased This creates mV/°C change output, allowing measurements 1000°C.
0.1µF
Figure shows low-side monitor equivalent. this circuit, input common-mode voltage AD8572 near ground. Again, resistor provides voltage drop proportional return current. output voltage given
VOUT SENSE
(24)
component values shown Figure output transfer function decreases from -2.5 V/A.
RSENSE 0.1µF
REF02EZ
10.7k
1N4148
40.2k
124k
10µF
Si9433 MONITOR OUTPUT
AD8572
01104-066
5.62k
53.6k
(0°C 500°C)
Figure High-Side Load Current Monitor
Figure Precision K-Type Thermocouple Amplifier with Cold-Junction Compensation
PRECISION CURRENT METER
Because input bias current superb offset voltage single-supply voltages, AD857x excellent amplifier precision current monitoring. rail-to-rail input allows amplifier used either high-side low-side current monitor. Using both amplifiers AD8572 provides simple method monitor both current supply return paths load fault detection. Figure shows high-side current monitor configuration. Here, input common-mode voltage amplifier near positive supply voltage. rail-to-rail input amplifier provides precise measurement, even with input common-mode voltage supply voltage. CMOS input structure does draw input bias current, ensuring minimum measurement error. resistor creates voltage drop noninverting input AD857x. output amplifier corrected until this voltage appears inverting input. This creates current through that turn flows through monitor output given
Monitor Output SENSE
2.49k VOUT
AD8572
RETURN GROUND
01104-068
RSENSE
Figure Low-Side Load Current Monitor
PRECISION VOLTAGE COMPARATOR
AD857x operated open-loop used precision comparator. AD857x less than offset voltage when this configuration. slight increase offset voltage stems from fact that autocorrection architecture operates with lowest offset closed-loop configuration, that with negative feedback. With overdrive, device propagation delay rising edge falling edge. Care should taken ensure maximum differential voltage device exceeded. more information, refer Input Overvoltage Protection section.
(23)
Using components shown Figure monitor output transfer function V/A.
Rev. Page
01104-067
K-TYPE THERMOCOUPLE 40.7µV/°C
2.74k
0.1µF
AD8572
2.49k
AD8571/AD8572/AD8574 OUTLINE DIMENSIONS
3.20 3.00 2.80
3.10 3.00 2.90
3.20 3.00 2.80
5.15 4.90 4.65
4.50 4.40 4.30
6.40
0.65 0.95 0.85 0.75 0.15 0.00 0.38 0.22 SEATING PLANE 1.10 0.80 0.60 0.40
0.65 0.15 0.05 COPLANARITY 0.10 0.30 0.19 1.20 SEATING 0.20 PLANE 0.09
0.23 0.08
COPLANARITY 0.10
0.75 0.60 0.45
COMPLIANT JEDEC STANDARDS MO-153-AA
COMPLIANT JEDEC STANDARDS MO-187-AA
Figure 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown millimeters
Figure 8-Lead Thin Shrink Small Outline Package [TSSOP] (RU-8) Dimensions shown millimeters
5.00 (0.1968) 4.80 (0.1890)
5.10 5.00 4.90
4.00 (0.1574) 3.80 (0.1497)
6.20 (0.2440) 5.80 (0.2284)
4.50 4.40 4.30
6.40
1.27 (0.0500) 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE
1.75 (0.0688) 1.35 (0.0532)
0.50 (0.0196) 0.25 (0.0099) 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157)
1.05 1.00 0.80
0.51 (0.0201) 0.31 (0.0122)
0.65 1.20 0.15 0.05 0.30 0.19
0.20 0.09
COMPLIANT JEDEC STANDARDS MS-012-A CONTROLLING DIMENSIONS MILLIMETERS; INCH DIMENSIONS PARENTHESES) ROUNDED-OFF MILLIMETER EQUIVALENTS REFERENCE ONLY APPROPRIATE DESIGN.
060506-A
SEATING COPLANARITY PLANE 0.10
0.75 0.60 0.45
COMPLIANT JEDEC STANDARDS MO-153-AB-1
Figure 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown millimeters inches
Figure 14-Lead Thin Shrink Small Outline Package [TSSOP] (RU-14) Dimensions shown millimeters
Rev. Page
AD8571/AD8572/AD8574
8.75 (0.3445) 8.55 (0.3366)
4.00 (0.1575) 3.80 (0.1496)
6.20 (0.2441) 5.80 (0.2283)
1.27 (0.0500) 0.25 (0.0098) 0.10 (0.0039) COPLANARITY 0.10 0.51 (0.0201) 0.31 (0.0122)
1.75 (0.0689) 1.35 (0.0531) SEATING PLANE
0.50 (0.0197) 0.25 (0.0098) 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157)
COMPLIANT JEDEC STANDARDS MS-012-AB CONTROLLING DIMENSIONS MILLIMETERS; INCH DIMENSIONS PARENTHESES) ROUNDED-OFF MILLIMETER EQUIVALENTS REFERENCE ONLY APPROPRIATE DESIGN.
Figure 14-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-14) Dimensions shown millimeters (inches)
ORDERING GUIDE
Model AD8571AR AD8571AR-REEL AD8571AR-REEL7 AD8571ARZ AD8571ARZ-REEL1 AD8571ARZ-REEL71 AD8571ARM-R2 AD8571ARM-REEL AD8571ARMZ-R21 AD8571ARMZ-REEL1 AD8572AR AD8572AR-REEL AD8572AR-REEL7 AD8572ARZ1 AD8572ARZ-REEL1 AD8572ARZ-REEL71 AD8572ARU AD8572ARU-REEL AD8572ARUZ1 AD8572ARUZ-REEL1 AD8574AR AD8574AR-REEL AD8574AR-REEL7 AD8574ARZ1 AD8574ARZ-REEL1 AD8574ARZ-REEL71 AD8574ARU AD8574ARU-REEL AD8574ARUZ1 AD8574ARUZ-REEL1
Temperature Range -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C -40°C +125°C
Package Description 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead TSSOP 8-Lead TSSOP 8-Lead TSSOP 8-Lead TSSOP 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead TSSOP 14-Lead TSSOP 14-Lead TSSOP 14-Lead TSSOP
Package Option RM-8 RM-8 RM-8 RM-8 RU-8 RU-8 RU-8 RU-8 R-14 R-14 R-14 R-14 R-14 R-14 RU-14 RU-14 RU-14 RU-14
060606-A
Branding
AJA#
Pb-free part, denote lead-free product bottom marked.
Rev. Page
AD8571/AD8572/AD8574 NOTES
©2006 Analog Devices, Inc. rights reserved. Trademarks registered trademarks property their respective owners. C01104-0-9/06(B)
Rev. Page
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