AD8571AR ,Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational AmplifiersAPPLICATIONSTemperature Sensors8-Lead TSSOP 8-Lead SOICPressure Sensors(RU Suffix) (R Suffix)Precis ..
AD8571AR ,Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational AmplifiersCHARACTERISTICSOutput Voltage High V R = 100 kW to GND 2.685 2.697 VOH L–40
AD8571AR-AD8572AR-AD8572ARU-AD8574AR-AD8574ARU
Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers
REV.0
Zero-Drift, Single-Supply, Rail-to-Rail
Input/Output Operational Amplifiers
8-Lead SOIC
(R Suffix)
14-Lead SOIC
(R Suffix)
FEATURES
Low Offset Voltage: 1 mV
Input Offset Drift: 0.005 mV/8C
Rail-to-Rail Input and Output Swing
5 V/2.7 V Single-Supply Operation
High Gain, CMRR, PSRR: 130 dB
Ultralow Input Bias Current: 20 pA
Low Supply Current: 750 mA/Op Amp
Overload Recovery Time: 50 ms
No External Capacitors Required
APPLICATIONS
Temperature Sensors
Pressure Sensors
Precision Current Sensing
Strain Gage Amplifiers
Medical Instrumentation
Thermocouple Amplifiers
GENERAL DESCRIPTIONThis new family of amplifiers has ultralow offset, drift and bias
current. The AD8571, AD8572 and AD8574 are single, dual and
quad amplifiers featuring rail-to-rail input and output swings. All
are guaranteed to operate from 2.7 V to 5 V single supply.
The AD857x family provides the benefits previously found only in
expensive autozeroing or chopper-stabilized amplifiers. Using Analog
Devices’ new topology these new zero-drift amplifiers combine low
cost with high accuracy. (No external capacitors are required.) In
addition, using a patented spread-spectrum autozero technique, the
AD857x family virtually eliminates the intermodulation effects from
interaction of the chopping function with the signal frequency in ac
applications.
With an offset voltage of only 1 mV and drift of 0.005 mV/°C, the
AD8571 is perfectly suited for applications where error sources
cannot be tolerated. Position, and pressure sensors, medical
equipment, and strain gage amplifiers benefit greatly from nearly
zero drift over their operating temperature range. Many more
systems require the rail-to-rail input and output swings provided
by the AD857x family.
The AD857x family is specified for the extended industrial/automotive
(–40°C to +125°C) temperature range. The AD8571 single is
available in 8-lead MSOP and narrow 8-lead SOIC packages. The
AD8572 dual amplifier is available in 8-lead narrow SO and 8-lead
TSSOP surface mount packages. The AD8574 quad is available in
narrow 14-lead SOIC and 14-lead TSSOP packages.
8-Lead MSOP
(RM Suffix)
8-Lead TSSOP
(RU Suffix)
14-Lead TSSOP
(RU Suffix)
PIN CONFIGURATIONS
8-Lead SOIC
(R Suffix)
AD8571/AD8572/AD8574–SPECIFICATIONS
ELECTRICAL CHARACTERISTICSNOISE PERFORMANCE␣
NOTEGain testing is highly dependent upon test bandwidth.
Specifications subject to change without notice.
(VS = 5 V, VCM = 2.5 V, VO = 2.5 V, TA = 258C unless otherwise noted)
AD8571/AD8572/AD8574
ELECTRICAL CHARACTERISTICSNOISE PERFORMANCE␣
NOTEGain testing is highly dependent upon test bandwidth.
Specifications subject to change without notice.
(VS = 2.7 V, VCM = 1.35 V, VO = 1.35 V, TA = 258C unless otherwise noted)
AD8571/AD8572/AD8574
ABSOLUTE MAXIMUM RATINGSSupply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 V
Input Voltage . . . . . . . . . . . . . . . . . . . . . .GND to VS + 0.3 V
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . .–5.0 V
ESD (Human Body Model) . . . . . . . . . . . . . . . . . . . . .2,000 V
Output Short-Circuit Duration to GND . . . . . . . . .Indefinite
Storage Temperature Range
RM, RU and R Packages . . . . . . . . . . . . .–65°C to +150°C
Operating Temperature Range
AD8571A/AD8572A/AD8574A . . . . . . . .–40°C to +125°C
Junction Temperature Range
RM, RU and R Packages . . . . . . . . . . . . .–65°C to +150°C
Lead Temperature Range (Soldering, 60 sec) . . . . . . . .300°C
NOTESStresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational sections
of this specification is not implied. Exposure to absolute maximum rating condi-
tions for extended periods may affect device reliability.Differential input voltage is limited to –5.0 V or the supply voltage, whichever is less.
NOTEqJA is specified for worst-case conditions, i.e., qJA is specified for device in socket
for P-DIP packages, qJA is specified for device soldered in circuit board for
SOIC and TSSOP packages.
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD8571/AD8572/AD8574 features proprietary ESD protection circuitry, permanent damage
may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
ORDERING GUIDENOTESDue to package size limitations, these characters represent the part number.Available in reels only. 1,000 or 2,500 pieces per reel.Available in reels only. 2,500 pieces per reel.
Figure 1.Input Offset Voltage
Distribution at 2.7 V
Figure 4.Input Offset Voltage
Distribution at 5 V
LOAD CURRENT – mA
OUTPUT VOLTAGE – mV
10k
0.00010.01 Figure 7.Output Voltage to Supply
Rail vs. Output Current at 2.7 V
Figure 2.Input Bias Current vs.
Common-Mode Voltage
INPUT OFFSET DRIFT – nV/8C
NUMBER OF AMPLIFIERS62345 Figure 5.Input Offset Voltage Drift
Distribution at 5 V
TEMPERATURE – 8C
INPUT BIAS CURRENT –
1,000275250
125225
0255075100
150Figure 8.Bias Current vs. Temperature
Figure 3.Input Bias Current vs.
Common-Mode Voltage
Figure 6.Output Voltage to Supply
Rail vs. Output Current at 5 V
Figure 9.Supply Current vs.
Temperature
AD8571/AD8572/AD8574
SUPPLY VOLTAGE – V
SUPPLY CURRENT PER AMPLIFIER – 800
500162345 Figure 10.Supply Current vs.
Supply Voltage
FREQUENCY – Hz
CLOSED-LOOP GAIN – dB
1001k10M10k100k1M240
Figure 13.Closed Loop Gain vs.
Frequency at 2.7 V
FREQUENCY – Hz
OUTPUT IMPEDANCE –
1001k10M10k100k1M
120 Figure 16.Output Impedance vs.
Frequency at 5 V
Figure 11.Open-Loop Gain and
Phase Shift vs. Frequency at 2.7 V
FREQUENCY – Hz
CLOSED-LOOP GAIN – dB
1001k10M10k100k1M240
Figure 14.Closed Loop Gain vs.
Frequency at 5 V
Figure 17.Large Signal Transient
Response at 2.7 V
Figure 12.Open-Loop Gain and
Phase Shift vs. Frequency at 5 V
FREQUENCY – Hz
OUTPUT IMPEDANCE –
1001k10M10k100k1M
120 Figure 15.Output Impedance vs.
Frequency at 2.7 V
Figure 18.Large Signal Transient
Response at 5 V
Figure 19.Small Signal Transient
Response at 2.7 V
Figure 22.Small Signal Overshoot
vs. Load Capacitance at 5 V
Figure 25.No Phase Reversal
Figure 20.Small Signal Transient
Response at 5 V
Figure 23.Positive Overvoltage
Recovery
FREQUENCY – Hz
CMRR – dB
1401001k10M10k100k1M
100 Figure 26.CMRR vs. Frequency
at 2.7 V
Figure 21.Small Signal Overshoot
vs. Load Capacitance at 2.7 V
Figure 24.Negative Overvoltage
Recovery
Figure 27.CMRR vs. Frequency
at 5 V
AD8571/AD8572/AD8574
FREQUENCY – Hz
PSRR – dB
1401001k10M10k100k1M
100 Figure 28.PSRR vs. Frequency
at –1.35 V
FREQUENCY – Hz
OUTPUT SWING – V p-p
2.51001k1M10k100k
5.5 Figure 31.Maximum Output Swing
vs. Frequency at 5 V
– nV/ Hz
FREQUENCY – kHz
1.01.52.02.50 Figure 34.Voltage Noise Density at
2.7 V from 0 Hz to 2.5 kHz
FREQUENCY – Hz
PSRR – dB
1401001k10M10k100k1M
100 Figure 29.PSRR vs. Frequency
at –2.5 V
Figure 32.0.1 Hz to 10 Hz Noise
at 2.7 V
– nV/ Hz
FREQUENCY – kHz1520250 Figure 35.Voltage Noise Density at
2.7 V from 0 Hz to 25 kHz
Figure 30.Maximum Output Swing
vs. Frequency at 2.7 V
Figure 33.0.1 Hz to 10 Hz Noise at 5 V
Figure 36.Voltage Noise Density at
5 V from 0 Hz to 2.5 kHz
– nV/ Hz
FREQUENCY – kHz Figure 37.Voltage Noise Density
at 5 V from 0 Hz to 25 kHz
TEMPERATURE – 8C
SHORT-CIRCUIT CURRENT – mA
250275250
125225
0255075100
150220
Figure 40.Output Short-Circuit
Current vs. Temperature
TEMPERATURE – 8C
OUTPUT VOLTAGE SWING – mV
200275250
125225
0255075100
225 Figure 43.Output Voltage to Supply
Rail vs. Temperature
– nV/ Hz
FREQUENCY – Hz
210 Figure 38.Voltage Noise Density
at 5 V from 0 Hz to 10 Hz
TEMPERATURE – 8C
SHORT-CIRCUIT CURRENT – mA
100
2100275250
125225
0255075100
150240
Figure 41.Output Short-Circuit
Current vs. Temperature
Figure 39.Power-Supply Rejection
vs. Temperature
Figure 42.Output Voltage to
Supply Rail vs. Temperature
AD8571/AD8572/AD8574
FUNCTIONAL DESCRIPTIONThe AD857x family are CMOS amplifiers that achieve their
high degree of precision through random frequency autozero
stabilization. The autocorrection topology allows the AD857x
to maintain its low offset voltage over a wide temperature range,
and the randomized autozero clock eliminates any intermodulation
distortion (IMD) errors at the amplifier’s output.
The AD857x can be run from a single supply voltage as low as
2.7 V. The extremely low offset voltage of 1 mV and no IMD
products allows the amplifier to be easily configured for high
gains without risk of excessive output voltage errors. This makes
the AD857x an ideal amplifier for applications requiring both dc
precision and low distortion for ac signals. The extremely small
temperature drift of 5 nV/°C ensures a minimum of offset voltage
error over its entire temperature range of –40°C to +125°C. These
combined features make the AD857x an excellent choice for a
variety of sensitive measurement and automotive applications.
Amplifier ArchitectureEach AD857x op amp consists of two amplifiers, a main amplifier
and a secondary amplifier, used to correct the offset voltage of the
main amplifier. Both consist of a rail-to-rail input stage, allowing
the input common-mode voltage range to reach both supply rails.
The input stage consists of an NMOS differential pair operating
concurrently with a parallel PMOS differential pair. The outputs
from the differential input stages are combined in another gain
stage whose output is used to drive a rail-to-rail output stage.
The wide voltage swing of the amplifier is achieved by using two
output transistors in a common-source configuration. The output
voltage range is limited by the drain-to-source resistance of these
transistors. As the amplifier is required to source or sink more
output current, the voltage drop across these transistors increases
due to their rds. Simply put, the output voltage will not swing as
close to the rail under heavy output current conditions as it will
with light output current. This is a characteristic of all rail-to-rail
output amplifiers. Figures 6 and 7 show how close the output
voltage can get to the rails with a given output current. The out-
put of the AD857x is short circuit protected to approximatelymA of current.
The AD857x amplifiers have exceptional gain, yielding greater
than 120 dB of open-loop gain with a load of 2 kW. Because the
output transistors are configured in a common-source configu-
ration, the gain of the output stage, and thus the open-loop gain
of the amplifier, is dependent on the load resistance. Open-loop
gain will decrease with smaller load resistances. This is another
characteristic of rail-to-rail output amplifiers.
Basic Autozero Amplifier TheoryAutocorrection amplifiers are not a new technology. Various IC
implementations have been available for over 15 years and some
improvements have been made over time. The AD857x design
offers a number of significant performance improvements over
older versions while attaining a very substantial reduction in
device cost. This section offers a simplified explanation of how
the AD857x is able to offer extremely low offset voltages and
high open-loop gains.
As noted in the previous section on amplifier architecture, each
AD857x op amp contains two internal amplifiers. One is used as
the primary amplifier, the other as an autocorrection, or nulling,
amplifier. Each amplifier has an associated input offset voltage
that can be modeled as a dc voltage source in series with the
noninverting input. In Figures 44 and 45 these are labeled as
VOSX, where x denotes the amplifier associated with the offset; A
for the nulling amplifier, B for the primary amplifier. The open-
loop gain for the +IN and –IN inputs of each amplifier is given
as AX. Both amplifiers also have a third voltage input with an
associated open-loop gain of BX.
There are two modes of operation determined by the action of
two sets of switches in the amplifier: An autozero phase and an
amplification phase.
Autozero PhaseIn this phase, all fA switches are closed and all fB switches are
opened. Here, the nulling amplifier is taken out of the gain loop
by shorting its two inputs together. Of course, there is a degree of
offset voltage, shown as VOSA, inherent in the nulling amplifier,
which maintains a potential difference between the +IN and –IN
inputs. The nulling amplifier feedback loop is closed through fA2
and VOSA appears at the output of the nulling amp and on CM1,
an internal capacitor in the AD857x. Mathematically, we can
express this in the time domain as:
which can be expressed as,
This shows us that the offset voltage of the nulling amplifier
times a gain factor appears at the output of the nulling amplifier
and thus on the CM1 capacitor.
VIN+
VIN2
VOUT
VNAFigure 44.Autozero Phase of the AD857x
Amplification PhaseWhen the fB switches close and the fA switches open for the
amplification phase, this offset voltage remains on CM1 and
essentially corrects any error from the nulling amplifier. The
voltage across CM1 is designated as VNA. Let us also designate
VIN as the potential difference between the two inputs to the
primary amplifier, or VIN = (VIN+ – VIN–). Now the output of the
nulling amplifier can be expressed as:
