AD8420BRMZ [ADI]
Wide Supply Range, Rail-to-Rail Output Instrumentation Amplifier; 宽电源电压范围，轨到轨输出仪表放大器
| 型号： | AD8420BRMZ |
| 厂家： | 
ADI |
| 描述： | Wide Supply Range, Rail-to-Rail Output Instrumentation Amplifier |
| 文件： | 总10页 (文件大小：247K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Wide Supply Range, Rail-to-Rail Output
Instrumentation Amplifier
Preliminary Technical Data
AD8420
FEATURES
PIN CONFIGURATION
Gain set with 2 external resistors
Gain range: 1 to 1000
NC
1
2
3
4
8
7
6
5
V
OUT
Input voltage goes below ground
Very wide power supply range
Single supply: 2.7V to 36V
Dual supply: +/-2.7V to+/-18V
Bandwidth (G=100): 2.5 kHz
Input noise: 50 nV/√Hz
Max supply current: 90 µA
Max offset voltage: 200 uV
Max differential input voltage: 1V
Min CMRR: 100 dB
+IN
–IN
FB
REF
–V
S
+V
S
AD8420
TOP VIEW
(Not to Scale)
Figure 1.
Table 1. Instrumentation Amplifiers by Category1
MSOP-8 package
General
Purpose
AD8221/2
AD8220/4
AD8228
Zero
Drift
Military
Grade
Low
Power
AD8420
AD8235/6 AD8251
AD627 AD8253
AD8226/7 AD8231
AD623
AD8223
Digital
Gain
AD8250
APPLICATIONS
Bridge amplifiers
Pressure Measurement
Medical instrumentation
Portable data acquisition
Multichannel systems
AD8231 AD620
AD8290 AD621
AD8293 AD524
AD8553 AD526
AD8556 AD624
AD8557
AD8295
1 See www.analog.com for the latest instrumentation amplifiers.
GENERAL DESCRIPTION
The AD8420 can operate off both single or dual supplies. It
works well for a portable system with a limited single supply
voltage and equally well for a system using large dual supplies.
The AD8420 is a low cost, wide supply range amplifier that uses
two resistors to set any gain between 1 and 1000. It is optimized
to amplify small differential voltages in the presence of large
common mode signals.
Gain is set using the ratio of two resistors. A reference pin
allows the user to offset the output voltage. This feature is useful
when the output signal needs to be centered around a specific
voltage, such as mid-supply.
The AD8420 is based on a current mode architecture that gives
it excellent input common mode range. Unlike conventional
instrumentation amplifiers, the AD8420 can easily amplify
signals at or even slightly below ground without requiring dual
supplies. The AD8420 has a full rail to rail output, and the
output voltage is completely independent of the input common
mode voltage.
The AD8420 is available in an 8 pin MSOP package.
Performance is specified over the full temperature range of
−40°C to +85°C. Part is operational from −40°C to +125°C
Rev. PrD
Information 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
rightsof third parties that may result fromits 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 andregisteredtrademarks 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
Fax: 781.461.3113
www.analog.com
©2011 Analog Devices, Inc. All rights reserved.
AD8420
Preliminary Technical Data
SPECIFICATIONS
+VS = +5V, −VS = 0V, V REF = 0 V, VIN+=0V, VIN-=0V, TA = 25°C, G = 1 to 1000, RL = 20 kΩ, specifications referred to input, unless
otherwise noted
Table 2.
Parameter
Conditions
Min
Typ
Max
Unit
COMMON-MODE REJECTION RATIO (CMRR)
CMRR DC to 60 Hz
CMRR at 1 kHz
VCM = 0 V to 2.7 V
100
dB
dB
NOISE
Voltage Noise
Spectral Density
Peak to Peak
f = 1 kHz, VDIFF ≤100 mV
f = 0.1 Hz to 10 Hz, VDIFF ≤ 100 mV
50
1.5
nV/√Hz
µV p-p
Current Noise
Spectral Density
Peak to Peak
f = 1 kHz
f = 0.1 Hz to 10 Hz
fA/√Hz
pA p-p
VOLTAGE OFFSET
Offset
200
1
µV
µV/°C
dB
Average Temperature Coefficient
Offset RTI vs. Supply (PSR)
INPUTS
TA = −40°C to +85°C
Valid for REF & FB pair, as well as +IN & -IN
TA = +25°C
TA = +85°C
TA = −40°C
TA = −40°C to +85°C
TA = +25°C
Input Bias Current1
25
1
40
nA
nA
nA
pA/°C
nA
Average Temperature Coefficient
Input Offset Current
TA = +85°C
nA
TA = −40°C
nA
Average Temperature Coefficient
Input Impedance
TA = −40°C to +85°C
pA/°C
Differential
130||2
MΩ||pF
Common Mode
1000||2
MΩ||pF
Differential Input Operating Voltage
Input Operating Voltage (+IN, -IN, or REF)
TA = –40°C to +85°C
TA = +25°C
TA = +85°C
-1
1
V
V
V
V
−VS – 0.15
−VS – 0.05
−VS – 0.2
+VS −2.2
+VS – 1.8
+VS – 2.7
TA = –40°C
DYNAMIC RESPONSE
Small Signal –3 dB Bandwidth
G = 1
250
25
2.5
kHz
kHz
kHz
kHz
G = 10
G = 100
G =1000
0.25
Settling Time 0.01%
G = 10
4 V step
µs
G = 100
µs
G = 1000
µs
Slew Rate
Exceeds Bandwidth Limit
V/µs
Rev. PrD | Page 2 of 2
Preliminary Technical Data
AD8420
GAIN2
G = 1 + (R2/R1)
Gain Range
Gain Error
Gain vs. Temperature
OUTPUT
1
1000
0.05
10
V/V
%
ppm/°C
VOUT = 0.2V to 4.8V
TA = −40°C to +85°C
Output Swing
RL = 10 kΩ to mid supply
TA = +25°C
TA = +85°C
TA = –40°C
−VS + 0.15
−VS + 0.1
+VS – 0.15
+VS – 0.1
V
V
V
RL = 100 kΩ to mid supply
TA = +25°C
TA = +85°C
TA = –40°C
V
V
V
Short-Circuit Current
POWER SUPPLY
Operating Range
Quiescent Current
10
mA
Single supply operation3
TA = +25°C
TA = –40°C
TA = +85°C
2.7
36
90
V
75
µA
µA
µA
µA
TA = +85°C
100
TEMPERATURE RANGE
Specified
Operational4
−40
−40
+85
+125
°C
°C
1 The input stage uses pnp transistors, so input bias current always flows out of the part.
2 For G>1, errors from external resistors R1 and R2 should be added to these specifications, including error from FB pin bias current.
3 Minimum supply voltage indicated for V+IN, V-IN, VREF= 0V.
.
4 See Typical Performance Curves for operation between 85°C and 125°C
Rev. PrD | Page 3 of 3
AD8420
Preliminary Technical Data
+VS = +15 V, −VS = −15 V, VREF = 0 V, TA = 25°C, G = 1 to 1000, RL = 20 kΩ, specifications referred to input, unless otherwise noted
Table 3.
Parameter
Conditions
Min
Typ
Max
Unit
COMMON-MODE REJECTION RATIO (CMRR)
VCM = –10 V to +10 V
CMRR DC to 60 Hz
CMRR at 1 kHz
NOISE
100
dB
dB
Voltage Noise
Spectral Density
Peak to Peak
f = 1 kHz, VDIFF ≤ 100 mV
f = 0.1 Hz to 10 Hz, VDIFF ≤ 100 mV
50
1.5
nV/√Hz
µV p-p
Current Noise
Spectral Density
Peak to Peak
f = 1 kHz
f = 0.1 Hz to 10 Hz
fA/√Hz
pA p-p
VOLTAGE OFFSET
Offset
VS = 5 V to 15 V
TA = −40°C to +85°C
200
1
µV
µV/°C
dB
Average Temperature Coefficient
Offset RTI vs. Supply (PSR)
INPUTS
Valid for REF & FB pair, as well as +IN & -IN
TA = +25°C
TA = +85°C
TA = −40°C
TA = −40°C to +85°C
TA = +25°C
Input Bias Current1
25
40
1
nA
nA
nA
pA/°C
nA
Average Temperature Coefficient
Input Offset Current
TA = +85°C
nA
TA = −40°C
nA
Average Temperature Coefficient
Input Impedance
TA = −40°C to +85°C
pA/°C
Differential
130||3
MΩ||pF
Common Mode
1000||3
MΩ||pF
Differential Input Operating Voltage
Input Operating Voltage (+IN, -IN, or REF)
TA = –40°C to +85°C
TA = +25°C
TA = +85°C
-1
1
V
V
V
V
−VS – 0.15
−VS – 0.05
−VS – 0.2
+VS −2.2
+VS – 1.8
+VS – 2.7
TA = –40°C
DYNAMIC RESPONSE
Check voltage differential
Small Signal –3 dB Bandwidth
G = 1
G = 10
G = 100
G =1000
Settling Time 0.01%
G = 1
250
25
2.5
kHz
kHz
kHz
kHz
0.25
10 V step
µs
G = 10
µs
G = 100
µs
G = 1000
Slew Rate
µs
V/µs
Exceeds Bandwidth Limit
Rev. PrD | Page 4 of 4
Preliminary Technical Data
AD8420
GAIN2
G = 1 + (R2/R1)
Gain Range
Gain Error
1
1000
0.05
V/V
%
VOUT 10 V
Gain Nonlinearity
G = 1 to 10
VOUT = –10 V to +10 V
RL ≥ 20 kΩ
ppm
G = 100
ppm
RL ≥ 20 kΩ
G = 1000
ppm
RL ≥ 20 kΩ
Gain vs. Temperature
OUTPUT
TA = −40°C to +85°C
10
ppm/°C
Output Swing
RL = 20 kΩ to ground
TA = +25°C
TA = +85°C
TA = –40°C
−VS + 0.15
−VS + 0.1
+VS – 0.15
+VS – 0.1
V
V
V
RL = 100 kΩ to ground
TA = +25°C
TA = +85°C
TA = –40°C
V
V
V
Short-Circuit Current
POWER SUPPLY
Operating Range
Quiescent Current
10
mA
Dual supply operation3
TA = +25°C
TA = –40°C
TA = +85°C
2.7
18V
90
V
75
µA
µA
µA
100
TEMPERATURE RANGE
Specified
Operational4
−40
−40
+85
+125
°C
°C
1 The input stage uses pnp transistors, so input bias current always flows out of the part.
2 For G>1, errors from external resistors R1 and R2 should be added to these specifications, including error from FB pin bias current
3 Minimum positive supply voltage indicated for V+IN, V-IN, VREF= 0V. With V+IN, V-IN, VREF= -VS, minimum supply is 1.35V.
4 See Typical Performance Curves for operation between 85°C and 125°C
Rev. PrD | Page 5 of 5
AD8420
Preliminary Technical Data
ABSOLUTE MAXIMUM RATINGS
Table 4.
THERMAL RESISTANCE
θJA is specified for a device in free air.
Parameter
Rating
Supply Voltage
18 V
Table 5.
Output Short-Circuit Current
Maximum Voltage at −IN or +IN
Minimum Voltage at −IN or +IN
Maximum Voltage at REF
Minimum Voltage at REF
Storage Temperature Range
ESD
Indefinite
–Vs + 40V
+Vs – 40V
+Vs + 0.2V
–Vs – 0.2V
−65°C to +150°C
Package
θJA
Unit
8-Lead MSOP, 4-Layer JEDEC Board
135
°C/W
ESD CAUTION
Human Body Model
Charge Device Model
Machine Model
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Rev. PrD | Page 6 of 6
Preliminary Technical Data
AD8420
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
NC
1
2
3
4
8
7
6
5
V
OUT
+IN
–IN
FB
REF
–V
S
+V
S
AD8420
TOP VIEW
(Not to Scale)
Figure 2. Pin Configuration
Table 6. Pin Function Descriptions
Pin No.
Mnemonic Description
1
NC
This pin not connected internally. For best CMRR vs. frequency and leakage performance, connect this pin to
negative supply.
2
3
4
5
6
7
8
+IN
−IN
−VS
+VS
REF
FB
Positive Input.
Negative Input
Negative Supply.
Positive Supply.
Reference.
Feedback.
Output.
VOUT
Rev. PrD | Page 7 of 7
AD8420
Preliminary Technical Data
THEORY OF OPERATION
VOUT
A3
R2
+VS
VBIAS
ESD AND
OVERVOLTAGE
PROTECTION
FB
+IN
–IN
–VS
+VS
V
I
R1
V
I
ESD AND
OVERVOLTAGE
PROTECTION
REF
A1
A2
–VS
Figure 3. Simplified Schematic
ARCHITECTURE
Table 7. Suggested Resistors for Various Gains - 1% Resistors
R1 (kΩ)
R2 (kΩ)
short
49.9
80.6
90.9
95.3
97.6
100
Gain
1.00
2.00
5.03
10.09
20.06
49.8
101
The AD8420 consists of three amplifiers: two matched
transconductance amplifiers that convert voltage to current and
one integrator amplifier that converts current to voltage.
none
49.9
20
10
5
2
1
1
1
1
The AD8420 works as follows: assume a differential voltage is
applied across inputs +IN and -IN. This input voltage is
converted into a current by Amplifier A1. This will create a
difference in current between A1 and A2, which is fed into A3.
A3’s output voltage will change until A2 sinks all the current A1
is generating. Because the gain of A1 and A2 are matched, this
means the differential input voltage across A1 will appear across
the inputs of A2. Gain is set by the ratio of R2 to R1.
200
499
1000
201
500
1001
While the ratio of R2 to R1 sets the gain, the absolute value of
the resistors is up to the designer. Larger values reduce power
consumption and output loading; smaller values limit FB input
bias current error.
Because the AD8420 converts the input differential signals to a
current, there are no internal headroom issues as with
traditional instrumentation amplifier architectures. This is
particularly important when amplifying a signal with a
common mode voltage near one of the supply rails.
A method that allows large value feedback resistors while
limiting FB bias current error is to place a resistor of value
R1||R2 in series with the REF terminal as shown in Figure 4. At
higher gains, this resistor can simply be the same value as R1.
To improve robustness and ease of use, the AD8420 includes
overvoltage protection on its inputs. This protection scheme
allows input voltages well beyond the supply rails (as well as
wide differential input voltages) without damaging the part.
AD8420
VOUT
R2
FB
SETTING THE GAIN
+IN
R1
The transfer function of the AD8420 is
–IN
REF
VOUT = G(VIN+ − VIN−) + VREF
R1||R2
where:
VREF
R2
R1
R2
G = 1+
G = 1 +
R1
Figure 4. Cancelling Out Error from FB Input Bias Current
Rev. PrD | Page 8 of 8
Preliminary Technical Data
AD8420
INPUT VOLTAGE RANGE
DRIVING THE REFERENCE PIN
Unlike traditional instrumentation amplifier architectures, the
allowed input range of the AD8420 is simplicity itself. For the
AD8420’s transfer function to be valid, the input voltage should
follow two rules:
Traditional instrumentation amplifier architectures require the
reference pin to be driven with a low impedance source. In
traditional architectures, impedance at the reference pin
degrades both CMRR and gain accuracy. With the AD8420
architecture, resistance at the reference pin has no effect on
CMRR.
1) Keep differential input voltage within 1V.
2) Keep voltage on +IN, -IN, and REF pins in specified
input voltage range
AD8420
VOUT
No hexagonal figures. No complicated formulas.
R2
FB
INPUT PROTECTION
+IN
R1
The AD8420 has very robust inputs and typically does not
need additional input protection. Input voltages can be up to
40 V from the opposite supply rail. For example, with a +5 V
positive supply and a −8 V negative supply, the part can safely
withstand voltages from −35 V to 32 V. The part can handle
large differential input voltages, even when the part is in high
gain, without damage.
–IN
REF
RREF
VREF
R2+RREF
R1
G = 1+
Figure 5. Calculating Gain with Reference Resistance
The rest of the AD8420 terminals should be kept within the
supplies. All terminals of the AD8426 are protected against ESD.
Resistance at the reference pin does affect the AD8420’s gain,
but if this resistance is constant, the gain setting resistors can be
adjusted to compensate. For example, the AD8420 can be
driven with a voltage divider as shown in Figure 6.
For applications that require protection beyond the AD8420’s
limits, place diodes at the AD8420 inputs to limit voltage and
resistors in series with the inputs to limit the current into these
diodes. To keep input bias current at minimum, low leakage
diode clamps such as the BAV199 should be used. The AD8420
also combines well with TVS diodes such as the PTVSxS1UR.
AD8420
VOUT
R2
FB
+IN
–IN
VS
R3
R1
REF
Optional
capacitor
filters noise
from Vs
R4
R2+R3||R4
R1
G = 1+
Figure 6. Using Resistor Divider to Set Reference Voltage
Rev. PrD | Page 9 of 9
AD8420
Preliminary Technical Data
OUTLINE DIMENSIONS
3.20
3.00
2.80
8
1
5
4
5.15
4.90
4.65
3.20
3.00
2.80
PIN 1
0.65 BSC
0.95
0.85
0.75
1.10 MAX
0.80
0.60
0.40
8°
0°
0.15
0.00
0.38
0.22
0.23
0.08
SEATING
PLANE
COPLANARITY
0.10
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 7. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
ORDERING GUIDE
Model1
Temperature Range
Package Description
Package
MSOP
MSOP
MSOP
MSOP
MSOP
MSOP
Branding
Y3Y
Y3Y
Y3Y
Y3Z
AD8420ARMZ
AD8420ARMZ-R7
AD8420ARMZ-RL
AD8420BRMZ
AD8420BRMZ-R7
AD8420BRMZ-RL
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Standard grade, tube
Standard grade, 7 inch Tape and Reel
Standard grade, 13 inch Tape and Reel
High performance grade, tube
High performance grade, 7 inch Tape and Reel
High performance grade, 13 inch Tape and Reel
Y3Z
Y3Z
1 Z = RoHS Compliant Part.
Rev. PrD | Page 10 of 10
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