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AD8276/77 Datasheet

Analog Devices Inc.

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Datasheet

Low Power, Wide Supply Range, Low Cost
Unity-Gain Difference Amplifiers
Data Sheet AD8276/AD8277
Rev. C
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
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
Fax: 781.461.3113 ©2009–2011 Analog Devices, Inc. All rights reserved.
FEATURES
Wide input range beyond supplies
Rugged input overvoltage protection
Low supply current: 200 μA maximum per channel
Low power dissipation: 0.5 mW at VS = 2.5 V
Bandwidth: 550 kHz
CMRR: 86 dB minimum, dc to 10 kHz
Low offset voltage drift: ±2 μV/°C maximum (B Grade)
Low gain drift: 1 ppm/°C maximum (B Grade)
Enhanced slew rate: 1.1 V/μs
Wide power supply range:
Single supply: 2 V to 36 V
Dual supplies: ±2 V to ±18 V
APPLICATIONS
Voltage measurement and monitoring
Current measurement and monitoring
Differential output instrumentation amplifier
Portable, battery-powered equipment
Test and measurement
GENERAL DESCRIPTION
The AD8276/AD8277 are general-purpose, unity-gain difference
amplifiers intended for precision signal conditioning in power
critical applications that require both high performance and low
power. They provide exceptional common-mode rejection ratio
(86 dB) and high bandwidth while amplifying signals well beyond
the supply rails. The on-chip resistors are laser-trimmed for
excellent gain accuracy and high CMRR. They also have extremely
low gain drift vs. temperature.
The common-mode range of the amplifiers extends to almost
double the supply voltage, making these amplifiers ideal for single-
supply applications that require a high common-mode voltage
range. The internal resistors and ESD circuitry at the inputs also
provide overvoltage protection to the op amps.
The AD8276/AD8277 are unity-gain stable. While they are
optimized for use as difference amplifiers, they can also be
connected in high precision, single-ended configurations with
G = −1, +1, +2. The AD8276/AD8277 provide an integrated
precision solution that has smaller size, lower cost, and better
performance than a discrete alternative.
The AD8276/AD8277 operate on single supplies (2.0 V to 36 V)
or dual supplies (±2 V to ±18 V). The maximum quiescent
supply current is 200 μA per channel, which is ideal for battery-
operated and portable systems.
FUNCTIONAL BLOCK DIAGRAM
07692-001
25
3 1
6
7
4
40k40k
40k
–VS
+VS
–IN
+IN
SENSE
OUT
REF
40k
AD8276
Figure 1. AD8276
07692-052
212
314
13
11
40k40k
40k
+VS
–INA
+INA
SENSEA
OUTA
REFA
40k
AD8277
610
5 8
9
4
40k40k
40k
–VS
–INB
+INB
SENSEB
OUTB
REFB
40k
Figure 2. AD8277
Table 1. Difference Amplifiers by Category
Low
Distortion
High
Voltage
Current
Sensing1 Low Power
AD8270 AD628 AD8202 (U) AD8276
AD8271 AD629 AD8203 (U) AD8277
AD8273 AD8205 (B) AD8278
AD8274 AD8206 (B)
AMP03 AD8216 (B)
1 U = unidirectional, B = bidirectional.
The AD8276 is available in the space-saving 8-lead MSOP and
SOIC packages, and the AD8277 is offered in a 14-lead SOIC
package. Both are specified for performance over the industrial
temperature range of −40°C to +85°C and are fully RoHS
compliant.
AD8276/AD8277 Data Sheet
Rev. C | Page 2 of 20
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Absolute Maximum Ratings ............................................................ 5
Thermal Resistance ...................................................................... 5
Maximum Power Dissipation ..................................................... 5
Short-Circuit Current .................................................................. 5
ESD Caution .................................................................................. 5
Pin Configurations and Function Descriptions ........................... 6
Typical Performance Characteristics ............................................. 8
Theory of Operation ...................................................................... 14
Circuit Information .................................................................... 14
Driving the AD8276/AD8277 .................................................. 14
Input Voltage Range ................................................................... 14
Power Supplies ............................................................................ 15
Applications Information .............................................................. 16
Configurations ............................................................................ 16
Differential Output .................................................................... 16
Current Source ............................................................................ 17
Voltage and Current Monitoring .............................................. 17
Instrumentation Amplifier........................................................ 18
RTD .............................................................................................. 18
Outline Dimensions ....................................................................... 19
Ordering Guide .......................................................................... 20
REVISION HISTORY
11/11—Rev. B to Rev. C
Change to Figure 53 ....................................................................... 18
4/10—Rev. A to Rev. B
Changes to Figure 53 ...................................................................... 18
Updated Outline Dimensions ....................................................... 19
7/09—Rev. 0 to Rev. A
Added AD8277 ................................................................... Universal
Changes to Features Section............................................................ 1
Changes to General Description Section ...................................... 1
Added Figure 2; Renumbered Sequentially .................................. 1
Changes to Specifications Section .................................................. 3
Changes to Figure 3 and Table 5 ..................................................... 5
Added Figure 5 and Table 7; Renumbered Sequentially ............. 7
Changes to Figure 10 ......................................................................... 8
Changes to Figure 34 ...................................................................... 12
Added Figure 36 ............................................................................. 13
Changes to Input Voltage Range Section .................................... 14
Changes to Power Supplies Section and Added Figure 40 ........ 15
Added to Figure 40 ......................................................................... 15
Changes to Differential Output Section ...................................... 16
Added Figure 47 and Changes to Current Source Section ....... 17
Added Voltage and Current Monitoring Section and Figure 49..... 17
Moved Instrumentation Amplifier Section and Added RTD
Section ........................................................................................................ 18
Changes to Ordering Guide .......................................................... 20
5/09—Revision 0: Initial Version
Data Sheet AD8276/AD8277
Rev. C | Page 3 of 20
SPECIFICATIONS
VS = ±5 V to ±15 V, V REF = 0 V, T A = 25°C, RL = 10 kΩ connected to ground, G = 1 difference amplifier configuration, unless
otherwise noted.
Table 2.
G = 1
Grade B
Grade A
Parameter Conditions Min Typ Max Min Typ Max Unit
INPUT CHARACTERISTICS
System Offset1 100 200 100 500 µV
vs. Temperature TA = −40°C to +85°C 200 500 µV
Average Temperature
Coefficient TA = −40°C to +85°C 0.5 2 2 5 µV/°C
vs. Power Supply
V
S
= ±5 V to ±18 V
5
10
µV/V
Common-Mode Rejection
Ratio (RTI)
VS = ±15 V, VCM = ±27 V,
RS = 0 Ω 86 80 dB
Input Voltage Range2 −2(VS + 0.1) +2(VS 1.5) −2(VS + 0.1) +2(VS 1.5) V
Impedance3
Differential
80
kΩ
Common Mode 40 40 kΩ
DYNAMIC PERFORMANCE
Bandwidth
550
kHz
Slew Rate 0.9 1.1 0.9 1.1 V/µs
Settling Time to 0.01% 10 V step on output,
CL = 100 pF
15 15 µs
Settling Time to 0.001% 16 16 µs
Channel Separation f = 1 kHz 130 130 dB
GAIN
Gain Error 0.005 0.02 0.01 0.05 %
Gain Drift TA = −40°C to +85°C 1 5 ppm/°C
Gain Nonlinearity VOUT = 20 V p-p 5 10 ppm
OUTPUT CHARACTERISTICS
Output Voltage Swing4
V
S
= ±15 V, R
L
= 10 kΩ,
TA = −40°C to +85°C −VS + 0.2 +VS − 0.2 −VS + 0.2 +VS − 0.2 V
Short-Circuit Current Limit ±15 ±15 mA
Capacitive Load Drive 200 200 pF
NOISE5
Output Voltage Noise f = 0.1 Hz to 10 Hz 2 2 μV p-p
f = 1 kHz 65 70 65 70 nV/√Hz
POWER SUPPLY
Supply Current6 200 200 μA
vs. Temperature TA = −40°C to +85°C 250 250 μA
Operating Voltage Range7 ±2 ±18 ±2 ±18 V
TEMPERATURE RANGE
Operating Range −40 +125 −40 +125 °C
1 Includes input bias and offset current errors, RTO (referred to output).
2 The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the Input Voltage Range section in the Theory of
Operation section for details.
3 Internal resistors are trimmed to be ratio matched and have ±20% absolute accuracy.
4 Output voltage swing varies with supply voltage and temperature. See Figure 18 through Figure 21 for details.
5 Includes amplifier voltage and current noise, as well as noise from internal resistors.
6 Supply current varies with supply voltage and temperature. See Figure 22 and Figure 24 for details.
7 Unbalanced dual supplies can be used, such as −VS = 0.5 V and +VS = +2 V. The positive supply rail must be at least 2 V above the negative supply and reference
voltage.
AD8276/AD8277 Data Sheet
Rev. C | Page 4 of 20
VS = +2.7 V to 5 V, V REF = midsupply, TA = 25°C, RL = 10 kΩ connected to midsupply, G = 1 difference amplifier configuration, unless
otherwise noted.
Table 3.
G = 1
Grade B Grade A
Parameter Conditions Min Typ Max Min Typ Max Unit
INPUT CHARACTERISTICS
System Offset1 100 200 100 500 µV
vs. Temperature TA = −40°C to +85°C 200 500 µV
Average Temperature
Coefficient TA = −40°C to +85°C 0.5 2 2 5 µV/°C
vs. Power Supply VS = ±5 V to ±18 V 5 10 µV/V
Common-Mode Rejection
Ratio (RTI)
VS = 2.7 V, VCM = 0 V
to 2.4 V, RS = 0 Ω 86 80 dB
VS = ±5 V, VCM = −10 V
to +7 V, RS = 0 Ω 86 80 dB
Input Voltage Range2 2(VS + 0.1) +2(VS 1.5) −2(VS + 0.1) +2(VS1.5) V
Impedance3
Differential 80 80 kΩ
Common Mode 40 40 kΩ
DYNAMIC PERFORMANCE
Bandwidth
450
kHz
Slew Rate 1.0 1.0 V/µs
Settling Time to 0.01% 8 V step on output,
CL = 100 pF, VS = 10 V
5 5 µs
Channel Separation f = 1 kHz 130 130 dB
GAIN
Gain Error 0.005 0.02 0.01 0.05 %
Gain Drift TA = −40°C to +85°C 1 5 ppm/°C
OUTPUT CHARACTERISTICS
Output Swing4 RL = 10 kΩ ,
TA = −40°C to +85°C −VS + 0.1 +VS − 0.15 −VS + 0.1 +VS − 0.15 V
Short-Circuit Current
Limit
±10 ±10 mA
Capacitive Load Drive 200 200 pF
NOISE5
Output Voltage Noise f = 0.1 Hz to 10 Hz 2 2 μV p-p
f = 1 kHz 65 65 nV/√Hz
POWER SUPPLY
Supply Current6 TA = −40°C to +85°C 200 200 μA
Operating Voltage
Range
2.0 36 2.0 36 V
TEMPERATURE RANGE
Operating Range −40 +125 −40 +125 °C
1 Includes input bias and offset current errors, RTO (referred to output).
2 The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the Input Voltage Range section in the Theory of Operation
section for details.
3 Internal resistors are trimmed to be ratio matched and have ±20% absolute accuracy.
4 Output voltage swing varies with supply voltage and temperature. See Figure 18 through Figure 21 for details.
5 Includes amplifier voltage and current noise, as well as noise from internal resistors.
6 Supply current varies with supply voltage and temperature. See Figure 23 and Figure 24 for details.
Data Sheet AD8276/AD8277
Rev. C | Page 5 of 20
ABSOLUTE MAXIMUM RATINGS
Table 4.
Parameter Rating
Supply Voltage ±18 V
Maximum Voltage at Any Input Pin −VS + 40 V
Minimum Voltage at Any Input Pin +VS − 40 V
Storage Temperature Range −65°C to +150°C
Specified Temperature Range −40°C to +85°C
Package Glass Transition Temperature (TG) 150°C
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.
THERMAL RESISTANCE
The θJA values in Table 5 assume a 4-layer JEDEC standard
board with zero airflow.
Table 5.
Package Type θJA Unit
8-Lead MSOP 135 °C/W
8-Lead SOIC 121 °C/W
14-Lead SOIC 105 °C/W
MAXIMUM POWER DISSIPATION
The maximum safe power dissipation for the AD8276/AD8277
is limited by the associated rise in junction temperature (TJ) on
the die. At approximately 150°C, which is the glass transition
temperature, the properties of the plastic change. Even temporarily
exceeding this temperature limit may change the stresses that the
package exerts on the die, permanently shifting the parametric
performance of the amplifiers. Exceeding a temperature of 150°C
for an extended period may result in a loss of functionality.
2.0
1.6
1.2
0.8
0.4
0
–50 0–25 25 50 75 100 125
MAXIMUM POWER DISSIPATION (W)
AMBIENT TEMERATURE (°C)
TJ MAX = 150°C
8-LEAD MSOP
θJA = 135°C/W
8-LEAD SOIC
θJA = 121°C/W
07692-002
14-LEAD SOIC
θJA = 105°C/W
Figure 3. Maximum Power Dissipation vs. Ambient Temperature
SHORT-CIRCUIT CURRENT
The AD8276/AD8277 have built-in, short-circuit protection
that limits the output current (see Figure 25 for more information).
While the short-circuit condition itself does not damage the
part, the heat generated by the condition can cause the part to
exceed its maximum junction temperature, with corresponding
negative effects on reliability. Figure 3 and Figure 25, combined
with knowledge of the supply voltages and ambient temperature of
the part, can be used to determine whether a short circuit will
cause the part to exceed its maximum junction temperature.
ESD CAUTION
AD8276/AD8277 Data Sheet
Rev. C | Page 6 of 20
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
REF
1
–IN
2
+IN
3
–VS
4
NC
8
+VS
7
OUT
6
SENSE
5
NC = NO CONNECT
AD8276
TOP VIEW
(Not to Scale)
07692-003
Figure 4. AD8276 8-Lead MSOP Pin Configuration
REF
1
–IN
2
+IN
3
–VS
4
NC
8
+VS
7
OUT
6
SENSE
5
NC = NO CONNECT
AD8276
TOP VIEW
(Not to Scale)
07692-004
Figure 5. AD8276 8-Lead SOIC Pin Configuration
Table 6. AD8276 Pin Function Descriptions
Pin No. Mnemonic Description
1
REF
Reference Voltage Input.
2 −IN Inverting Input.
3 +IN Noninverting Input.
4 −VS Negative Supply.
5 SENSE Sense Terminal.
6 OUT Output.
7
+VS
Positive Supply.
8 NC No Connect.
Data Sheet AD8276/AD8277
Rev. C | Page 7 of 20
NC
1
–INA
2
+INA
3
–VS
4
REFA
14
OUTA
13
SENSEA
12
+VS
11
+INB
5
SENSEB
10
–INB
6
OUTB
9
NC
7
REFB
8
NC = NO CONNECT
AD8277
TOP VIEW
(Not to Scale)
07692-053
Figure 6. AD8277 14-Lead SOIC Pin Configuration
Table 7. AD8277 Pin Function Descriptions
Pin No. Mnemonic Description
1 NC No Connect.
2 INA Channel A Inverting Input.
3
+INA
Channel A Noninverting Input.
4 VS Negative Supply.
5 +INB Channel B Noninverting Input.
6 INB Channel B Inverting Input.
7 NC No Connect.
8 REFB Channel B Reference Voltage Input.
9
OUTB
Channel B Output.
10 SENSEB Channel B Sense Terminal.
11 +VS Positive Supply.
12 SENSEA Channel A Sense Terminal.
13 OUTA Channel A Output.
14 REFA Channel A Reference Voltage Input.
AD8276/AD8277 Data Sheet
Rev. C | Page 8 of 20
TYPICAL PERFORMANCE CHARACTERISTICS
VS = ±15 V, T A = 25°C, RL = 10 kΩ connected to ground, G = 1 difference amplifier configuration, unless otherwise noted.
600
500
400
300
200
100
0
–300 –200 –100 0100 200 300
NUMBER OF HITS
SYSTEM OFFSET VOLTAGE (µV)
07692-005
N = 2042
MEAN = –2.28
SD = 32.7
Figure 7. Distribution of Typical System Offset Voltage
400
300
200
100
0
–90 –60 –30 030 60 90
NUMBER OF HITS
CMRR (µV/V)
07692-006
N = 2040
MEAN = –0.87
SD = 16.2
Figure 8. Distribution of Typical Common-Mode Rejection
4
2
0
–2
–4
–6
–8
–50 –35 –20 –5 10 25 40 55 70 85 90
CMRR (µV/V)
TEMPERATURE (°C)
REPRESENTATIVE DATA
07692-007
Figure 9. CMRR vs. Temperature, Normalized at 25°C
07692-008
80
–100
–80
–60
–40
–20
0
20
40
60
–50 –35 –20 –5 10 25 40 55 70 85
SYSTEM OFFSET (µV)
TEMPERATURE (°C)
Figure 10. System Offset vs. Temperature, Normalized at 25°C
20
–30
–25
–20
–15
–10
–5
0
5
10
15
GAIN ERROR (µV/V)
07692-009
–50 –35 –20 –5 10 25 40 55 70 85 90
TEMPERATURE (°C)
REPRESENTATIVE DATA
Figure 11. Gain Error vs. Temperature, Normalized at 25°C
10
0
–10
–20
–30
–40
–50
100 10M1M100k10k1k
GAIN (dB)
FREQUENCY (Hz)
V
S
= ±15V
V
S
= +2.7V
07692-010
Figure 12. Gain vs. Frequency, VS = ±15 V, +2.7 V
Data Sheet AD8276/AD8277
Rev. C | Page 9 of 20
120
100
80
60
40
20
011M100k10k1k10010
CMRR (dB)
FREQUENCY (Hz)
V
S
= ±15V
07692-011
Figure 13. CMRR vs. Frequency
120
100
80
60
40
20
011M100k10k1k10010
PSRR (dB)
FREQUENCY (Hz)
–PSRR
+PSRR
07692-012
Figure 14. PSRR vs. Frequency
30
20
10
0
–10
–20
–30
–20 20151050–5–10–15
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= ±5V
V
S
= ±15V
07692-013
Figure 15. Input Common-Mode Voltage vs. Output Voltage,
±15 V and ±5 V Supplies
8
4
6
2
0
–2
–4
–6
–0.5 0.5 1.5 2.5 3.5 4.5 5.5
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= 5V
V
REF
= MIDSUPPLY
V
S
= 2.7V
07692-014
Figure 16. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = Midsupply
8
4
6
2
0
–2
–4
–0.5 0.5 1.5 2.5 3.5 4.5 5.5
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= 5V
V
REF
= 0V
V
S
= 2.7V
07692-015
Figure 17. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = 0 V
+V
S
–0.1
–0.2
–0.3
–0.4
–V
S
+0.1
+0.2
+0.3
+0.4
21816141210864
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
SUPPLY VOLTAGE (±V
S
)
T
A
= –40°C
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
07692-016
Figure 18. Output Voltage Swing vs. Supply Voltage Per Channel and
Temperature, RL = 10 kΩ
AD8276/AD8277 Data Sheet
Rev. C | Page 10 of 20
+V
S
–0.2
–0.4
–0.6
–0.8
–1.0
–1.2
–V
S
+0.2
+0.4
+0.6
+0.8
+1.0
+1.2
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
SUPPLY VOLTAGE (±V
S
)
T
A
= –40°C
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
21816141210864
07692-017
Figure 19. Output Voltage Swing vs. Supply Voltage Per Channel and
Temperature, RL = 2 kΩ
+V
S
–4
–8
–V
S
+4
+8
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
LOAD RESISTANCE (Ω)
1k 100k10k
T
A
= –40°C
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
07692-018
Figure 20. Output Voltage Swing vs. RL and Temperature, VS = ±15 V
+V
S
–0.5
–1.0
–1.5
–2.0
–V
S
+0.5
+1.0
+1.5
+2.0
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
OUTPUT CURRENT (mA)
010987654321
T
A
= –40°C
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
07692-019
Figure 21. Output Voltage Swing vs. IOUT and Temperature, VS = ±15 V
180
160
170
150
140
130
120 018161412108642
SUPPLY CURRENT (µA)
SUPPLY VOLTAGE (±V)
07692-020
Figure 22. Supply Current Per Channel vs. Dual Supply Voltage, VIN = 0 V
180
160
170
150
140
130
120 0403530252015105
SUPPLY CURRENT (µA)
SUPPLY VOLTAGE (V)
07692-021
Figure 23. Supply Current Per Channel vs. Single-Supply Voltage, VIN = 0 V,
VREF = 0 V
250
150
200
100
50
0
–50 –30 –10 10 30 50 70 90 110 130
SUPPLY CURRENT (µA)
TEMPERATURE (°C)
VS = ±15V
VS = +2.7V
07692-022
VREF = MIDSUPPLY
Figure 24. Supply Current Per Channel vs. Temperature
Data Sheet AD8276/AD8277
Rev. C | Page 11 of 20
30
25
20
15
10
5
0
–5
–10
–15
–20
–50 –30 –10 10 30 50 70 90 110 130
SHORT-CIRCUIT CURRENT (mA)
TEMPERATURE (°C)
ISHORT+
ISHORT
07692-023
Figure 25. Short-Circuit Current Per Channel vs. Temperature
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–50 –30 –10 10 30 50 70 90 110 130
SLEW RATE (V/µs)
TEMPERATURE (°C)
–SR
+SR
07692-024
Figure 26. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz
8
6
4
2
0
–2
–4
–6
–8
–10 –8 –6 –4 –2 0246810
NONLINEARITY (2ppm/DIV)
OUTPUT VOLTAGE (V)
07692-025
Figure 27. Gain Nonlinearity, VS = ±15 V, RL2 kΩ
07692-026
0.002%/DIV
5V/DIV
11.24 µs TO 0.01%
13.84µs TO 0.001%
40µs/DIV
TIME (µs)
Figure 28. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = ±15 V
07692-027
0.002%/DIV
1V/DIV
4.34 µs TO 0.01%
5.12µs TO 0.001%
40µs/DIV
TIME (µs)
Figure 29. Large-Signal Pulse Response and Settling Time, 2 V Step,
VS = 2.7 V
07692-028
2V/DIV
10µs/DIV
Figure 30. Large-Signal Step Response
AD8276/AD8277 Data Sheet
Rev. C | Page 12 of 20
30
25
20
15
10
5
0
100 1k 10k 100k 1M
OUTPUT VOLTAGE (V p-p)
FREQUENCY (Hz)
V
S
= ±15V
V
S
= ±5V
07692-029
Figure 31. Maximum Output Voltage vs. Frequency, VS = ±15 V, ±5 V
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
100 1k 10k 100k 1M
OUTPUT VOLTAGE (V p-p)
FREQUENCY (Hz)
V
S
= 5V
V
S
= 2.7V
07692-030
Figure 32. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V
07692-050
20mV/DI
V
40µs/DIV
C
L
= 100pF
C
L
= 200pF
C
L
= 300pF
C
L
= 470pF
Figure 33. Small-Signal Step Response for Various Capacitive Loads
40
30
35
25
20
15
10
5
0
100 150 200 250 300 350 400
±2V
±5V
±15V ±18V
OVERSHOOT (%)
CAPACITIVE LOAD (pF)
07692-051
Figure 34. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ
1k
100
10
0.1 100k10k1k100101
NOISE (nV/ Hz)
FREQUENCY (Hz)
07692-034
Figure 35. Voltage Noise Density vs. Frequency
07692-035
1µV/DI
V
1s/DIV
Figure 36. 0.1 Hz to 10 Hz Voltage Noise
Data Sheet AD8276/AD8277
Rev. C | Page 13 of 20
160
0
20
40
60
80
100
120
140
1100k10k1k10010
CHANNEL SEPARATION (dB)
FREQUENCY (Hz)
07692-055
NO LOAD
10kΩ LOAD
2kΩ LOAD
1kΩ LOAD
Figure 37. Channel Separation
AD8276/AD8277 Data Sheet
Rev. C | Page 14 of 20
THEORY OF OPERATION
CIRCUIT INFORMATION
Each channel of the AD8276/AD8277 consists of a low power, low
noise op amp and four laser-trimmed on-chip resistors. These
resistors can be externally connected to make a variety of amplifier
configurations, including difference, noninverting, and inverting
configurations. Taking advantage of the integrated resistors of
the AD8276/AD8277 provides the designer with several benefits
over a discrete design, including smaller size, lower cost, and
better ac and dc performance.
25
3 1
6
7
4
40kΩ 40kΩ
40kΩ
–VS
+VS
IN–
IN+
SENSE
OUT
REF
AD8276
40kΩ
07692-031
Figure 38. Functional Block Diagram
DC Performance
Much of the dc performance of op amp circuits depends on the
accuracy of the surrounding resistors. Using superposition to
analyze a typical difference amplifier circuit, as is shown in
Figure 39, the output voltage is found to be
+
+
=+ R3
R4
V
R3
R4
R2R1
R2
VV ININ
OUT 1
This equation demonstrates that the gain accuracy and common-
mode rejection ratio of the AD8276/AD8277 is determined
primarily by the matching of resistor ratios. Even a 0.1% mismatch
in one resistor degrades the CMRR to 66 dB for a G = 1 difference
amplifier.
The difference amplifier output voltage equation can be reduced to
( )
+= N
IIN
OUT VV
R3
R4
V
as long as the following ratio of the resistors is tightly matched:
R3
R4
R1
R2 =
The resistors on the AD8276/AD8277 are laser trimmed to match
accurately. As a result, the AD8276/AD8277 provide superior
performance over a discrete solution, enabling better CMRR,
gain accuracy, and gain drift, even over a wide temperature range.
AC Performance
Component sizes and trace lengths are much smaller in an IC
than on a PCB, so the corresponding parasitic elements are also
smaller. This results in better ac performance of the AD8276/
AD8277. For example, the positive and negative input terminals
of the AD8276/AD8277 op amps are intentionally not pinned
out. By not connecting these nodes to the traces on the PCB, the
capacitance remains low, resulting in improved loop stability
and excellent common-mode rejection over frequency.
DRIVING THE AD8276/AD8277
Care should be taken to drive the AD8276/AD8277 with a low
impedance source: for example, another amplifier. Source
resistance of even a few kilohms (kΩ) can unbalance the resistor
ratios and, therefore, significantly degrade the gain accuracy and
common-mode rejection of the AD8276/AD8277. Because all
configurations present several kilohms of input resistance, the
AD8276/AD8277 do not require a high current drive from the
source and so are easy to drive.
INPUT VOLTAGE RANGE
The AD8276/AD8277 are able to measure input voltages beyond
the supply rails. The internal resistors divide down the voltage
before it reaches the internal op amp and provide protection to
the op amp inputs. Figure 39 shows an example of how the
voltage division works in a difference amplifier configuration.
For the AD8276/AD8277 to measure correctly, the input
voltages at the input nodes of the internal op amp must stay
below 1.5 V of the positive supply rail and can exceed the
negative supply rail by 0.1 V. Refer to the Power Supplies section
for more details.
R4
V
IN+
V
IN–
R3
R1
R2
R2
R1 + R2 (V
IN+
)
R2
R1 + R2 (V
IN+
)
07692-033
Figure 39. Voltage Division in the Difference Amplifier Configuration
The AD8276/AD8277 have integrated ESD diodes at the inputs
that provide overvoltage protection. This feature simplifies
system design by eliminating the need for additional external
protection circuitry, and enables a more robust system.
The voltages at any of the inputs of the parts can safely range
from +VS40 V up to −VS + 40 V. For example, on ±10 V
supplies, input voltages can go as high as ±30 V. Care should be
taken to not exceed the +VS − 40 V to −VS + 40 V input limits
to avoid risking damage to the parts.
Data Sheet AD8276/AD8277
Rev. C | Page 15 of 20
POWER SUPPLIES
The AD8276/AD8277 operate extremely well over a very wide
range of supply voltages. They can operate on a single supply as
low as 2 V and as high as 36 V, under appropriate setup conditions.
For best performance, the user must exercise care that the setup
conditions ensure that the internal op amp is biased correctly.
The internal input terminals of the op amp must have sufficient
voltage headroom to operate properly. Proper operation of the
part requires at least 1.5 V between the positive supply rail and
the op amp input terminals. This relationship is expressed in
the following equation:
V5.1+<
+
S
REF
VV
R2R1
R1
For example, when operating on a +VS = 2 V single supply and
VREF = 0 V, it can be seen from Figure 40 that the input terminals
of the op amp are biased at 0 V, allowing more than the required
1.5 V headroom. However, if VREF = 1 V under the same conditions,
the input terminals of the op amp are biased at 0.5 V, barely
allowing the required 1.5 V headroom. This setup does not allow
any practical voltage swing on the noninverting input. Therefore,
the user needs to increase the supply voltage or decrease VREF to
restore proper operation.
The AD8276/AD8277 are typically specified at single- and dual-
supplies, but they can be used with unbalanced supplies, as well;
for example, −VS = −5 V, + V S = 20 V. The difference between the
two supplies must be kept below 36 V. The positive supply rail
must be at least 2 V above the negative supply and reference
voltage.
R4
V
REF
R3
R1
R2
R1
R1 + R2(V
REF
)
R1
R1 + R2(V
REF
)
07692-032
Figure 40. Ensure Sufficient Voltage Headroom on the Internal Op Amp
Inputs
Use a stable dc voltage to power the AD8276/AD8277. Noise on
the supply pins can adversely affect performance. Place a bypass
capacitor of 0.1 µF between each supply pin and ground, as
close as possible to each supply pin. Use a tantalum capacitor
of 10 µF between each supply and ground. It can be farther
away from the supply pins and, typically, it can be shared by
other precision integrated circuits.
AD8276/AD8277 Data Sheet
Rev. C | Page 16 of 20
APPLICATIONS INFORMATION
CONFIGURATIONS
The AD8276/AD8277 can be configured in several ways (see
Figure 42 to Figure 46). All of these configurations have excellent
gain accuracy and gain drift because they rely on the internal
matched resistors. Note that Figure 43 shows the AD8276/AD8277
as difference amplifiers with a midsupply reference voltage at
the noninverting input. This allows the AD8276/AD8277 to be
used as a level shifter, which is appropriate in single-supply
applications that are referenced to midsupply.
As with the other inputs, the reference must be driven with a
low impedance source to maintain the internal resistor ratio. An
example using the low power, low noise OP1177 as a reference
is shown in Figure 41.
INCORRECT
V
CORRECT
AD8276
OP1177
+
VREF
AD8276
REF
07692-037
Figure 41. Driving the Reference Pin
40kΩ
2
3
5
1
6
40kΩ
40kΩ 40kΩ
–IN
OUT
+IN
V
OUT
= V
IN+
− V
IN−
07692-038
Figure 42. Difference Amplifier, Gain = 1
40kΩ
2
3
5
1
VREF = MIDSUPPLY
6
40kΩ
40kΩ 40kΩ
–IN
OUT
+IN
VOUT = VIN+ − VIN−
07692-039
Figure 43. Difference Amplifier, Gain = 1, Referenced to Midsupply
40kΩ
2
3
5
16
40kΩ
40kΩ
40kΩ
IN
OUT
VOUT = –VIN
07692-040
Figure 44. Inverting Amplifier, Gain = −1
40kΩ 5
1
2
3
6
40kΩ
40kΩ 40kΩ
OUT
IN
VOUT = VIN
07692-041
Figure 45. Noninverting Amplifier, Gain = 1
40kΩ
2 5
6
40kΩ
IN
OUT
3
1
40kΩ
40kΩ
V
OUT
= 2V
IN
07692-042
Figure 46. Noninverting Amplifier, Gain = 2
DIFFERENTIAL OUTPUT
Certain systems require a differential signal for better perfor-
mance, such as the inputs to differential analog-to-digital
converters. Figure 47 shows how the AD8276/AD8277 can
be used to convert a single-ended output from an AD8226
instrumentation amplifier into a differential signal. The internal
matched resistors of the AD8276 at the inverting input maximize
gain accuracy while generating a differential signal. The resistors at
the noninverting input can be used as a divider to set and track
the common-mode voltage accurately to midsupply, especially
when running on a single supply or in an environment where
the supply fluctuates. The resistors at the noninverting input
can also be shorted and set to any appropriate bias voltage. Note
that the VBIAS = VCM node indicated in Figure 47 is internal to
the AD8276 because it is not pinned out.
07692-043
AD8276
AD8226
V
REF
+IN
–IN
R
R
R
R
V
S
V
S
+
–OUT
+OUT
V
BIAS
= V
CM
Figure 47. Differential Output With Supply Tracking on Common-Mode
Voltage Reference
Data Sheet AD8276/AD8277
Rev. C | Page 17 of 20
The differential output voltage and common-mode voltage of
the AD8226 is shown in the following equations:
VDIFF_OUT = V+OUT V−OUT = GainAD8226 × (V+INV−IN)
VCM = (VS+ VS−)/2 = VBIAS
Refer to the AD8226 data sheet for additional information.
07692-056
212
314
13
11
40kΩ 40kΩ
40kΩ
+VS
–IN
+IN
+OUT
40kΩ
AD8277
610
58
9
4
40kΩ 40kΩ
40kΩ
–VS
40kΩ
–OUT
Figure 48. AD8277 Differential Output Configuration
The two difference amplifiers of the AD8277 can be configured
to provide a differential output, as shown in Figure 48. This
differential output configuration is suitable for various applications,
such as strain gage excitation and single-ended-to-differential
conversion. The differential output voltage has a gain of 2 as
shown in the following equation:
VDIFF_OUT = V+OUT V−OUT = 2 × (V+INV−IN)
CURRENT SOURCE
The AD8276 difference amplifier can be implemented as part
of a voltage-to-current converter or a precision constant current
source as shown in Figure 49. Using an integrated precision
solution such as the AD8276 provides several advantages over
a discrete solution, including space-saving, improved gain accuracy,
and temperature drift. The internal resistors are tightly matched
to minimize error and temperature drift. If the external resistors,
R1 and R2, are not well-matched, they become a significant
source of error in the system, so precision resistors are recom-
mended to maintain performance. The ADR821 provides a
precision voltage reference and integrated op amp that also
reduces error in the signal chain.
The AD8276 has rail-to-rail output capability that allows higher
current outputs.
REF
1
2
3
4
5
10
9
8
7
6
V–
V+
ADR821
40kΩ
40k
RLOAD
R1
R2
2N3904
40kΩ
40kΩ
V+
7
4
5
6
2
3
1
AD8276
–2.5V
IO = 2.5V(1/40kΩ + 1/R1)
R1 = R2
07692-046
Figure 49. Constant Current Source
VOLTAGE AND CURRENT MONITORING
Voltage and current monitoring is critical in the following
applications: power line metering, power line protection, motor
control applications, and battery monitoring. The AD8276/
AD8277 can be used to monitor voltages and currents in a
system, as shown in Figure 50. As the signals monitored by the
AD8276/AD8277 rise above or drop below critical levels, a
circuit event can be triggered to correct the situation or raise
a warning.
OP1177
07692-057
I
1
R
AD8276
I
3
I
C
R
AD8276
V
1
R
AD8276
V
3
R
AD8276
V
C
R
AD8276
8:1 ADC
Figure 50.Voltage and Current Monitoring in 3-Phase Power Line Protection
Using the AD8276
Figure 50 shows an example of how the AD8276 can be used to
monitor voltage and current on a 3-phase power supply. I1
through I3 are the currents to be monitored, and V1 through V3
are the voltages to be monitored on each phase. IC and VC are
the common or zero lines. Couplers or transformers interface
the power lines to the front-end circuitry and provide
attenuation, isolation, and protection.
On the current monitoring side, current transformers (CTs)
step down the power-line current and isolate the front-end
circuitry from the high voltage and high current lines. Across
the inputs of each difference amplifier is a shunt resistor that
converts the coupled current into a voltage. The value of the
AD8276/AD8277 Data Sheet
Rev. C | Page 18 of 20
resistor is determined by the characteristics of the coupler or
transformer and desired input voltage ranges to the AD8276.
On the voltage monitoring side, potential transformers (PTs)
are used to provide coupling and galvanic isolation. The PTs
present a load to the power line and step down the voltage to a
measureable level. The AD8276 helps to build a robust system
because it allows input voltages that are almost double its supply
voltage, while providing additional input protection in the form
of the integrated ESD diodes.
Not only does the AD8276 monitor the voltage and currents on
the power lines, it is able to reject very high common-mode
voltages that may appear at the inputs. The AD8276 also
performs the differential-to-single-ended conversion on the
input voltages. The 80differential input impedance that the
AD8276 presents is high enough that it should not load the
input signals.
07692-058
R
SH
I
SH
AD8276
V
OUT
= I
SH
× R
SH
Figure 51. AD8276 Monitoring Current Through a Shunt Resistor
Figure 51 shows how the AD8276 can be used to monitor the
current through a small shunt resistor. This is useful in power
critical applications such as motor control (current sense) and
battery monitoring.
INSTRUMENTATION AMPLIFIER
The AD8276/AD8277 can be used as building blocks for a low
power, low cost instrumentation amplifier. An instrumentation
amplifier provides high impedance inputs and delivers high
common-mode rejection. Combining the AD8276 with an
Analog Devices, Inc., low power amplifier (see Table 8) creates a
precise, power efficient voltage measurement solution suitable
for power critical systems.
R
G
R
F
R
F
–IN
+IN
A1
A2
AD8276
40kΩ
40kΩ
40kΩ
40kΩ
REF
V
OUT
V
OUT
= (1 + 2R
F
/R
G
) (V
IN+
– V
IN–
)
07692-045
Figure 52. Low Power Precision Instrumentation Amplifier
Table 8. Low Power Op Amps
Op Amp (A1, A2) Features
AD8506 Dual micropower op amp
AD8607 Precision dual micropower op amp
AD8617 Low cost CMOS micropower op amp
AD8667 Dual precision CMOS micropower op amp
It is preferable to use dual op amps for the high impedance inputs
because they have better matched performance and track each
other over temperature. The AD8276 difference amplifiers
cancel out common-mode errors from the input op amps, if
they track each other. The differential gain accuracy of the in-
amp is proportional to how well the input feedback resistors
(RF) match each other. The CMRR of the in-amp increases as
the differential gain is increased (1 + 2RF/RG), but a higher gain
also reduces the common-mode voltage range. Note that dual
supplies must be used for proper operation of this configuration.
Refer to A Designer’s Guide to Instrumentation Amplifiers for
more design ideas and considerations.
RTD
Resistive temperature detectors (RTDs) are often measured
remotely in industrial control systems. The wire lengths
needed to connect the RTD to a controller add significant
cost and resistance errors to the measurement. The AD8276
difference amplifier is effective in measuring errors caused by
wire resistance in remote 3-wire RTD systems, allowing the
user to cancel out the errors introduced by the wires. Its
excellent gain drift provides accurate measurements and stable
performance over a wide temperature range.
07692-059
AD8276
R
L2
R
L1
V
OUT
Σ-Δ
ADC
R
L3
R
T
I
EX
40k
40k40k
40k
Figure 53. 3-Wire RTD Cable Resistance Error Measurement
Data Sheet AD8276/AD8277
Rev. C | Page 19 of 20
OUTLINE DIMENSIONS
COMPLIANT TO JEDEC STANDARDS MO-187-AA
0.80
0.55
0.40
4
8
1
5
0.65 BSC
0.40
0.25
1.10 MAX
3.20
3.00
2.80
COPLANARITY
0.10
0.23
0.09
3.20
3.00
2.80
5.15
4.90
4.65
PIN 1
IDENTIFIER
15° MAX
0.95
0.85
0.75
0.15
0.05
10-07-2009-B
Figure 54. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DES
IGN.
COMPLIANT TO JEDEC STANDARDS MS-012-AA
012407-A
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
0.50 (0.0196)
0.25 (0.0099) 45°
1.75 (0.0688)
1.35 (0.0532)
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0040)
4
1
8 5
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2441)
5.80 (0.2284)
0.51 (0.0201)
0.31 (0.0122)
COPLANARITY
0.10
Figure 55. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body (R-8)
Dimensions shown in millimeters and (inches)
AD8276/AD8277 Data Sheet
Rev. C | Page 20 of 20
CONTROLLING DIMENSIONSARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
COMPLIANT TO JEDEC STANDARDS MS-012-AB
060606-A
14 8
7
1
6.20 (0.2441)
5.80 (0.2283)
4.00 (0.1575)
3.80 (0.1496)
8.75 (0.3445)
8.55 (0.3366)
1.27 (0.0500)
BSC
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0039)
0.51 (0.0201)
0.31 (0.0122)
1.75 (0.0689)
1.35 (0.0531)
0.50 (0.0197)
0.25 (0.0098)
1.27 (0.0500)
0.40 (0.0157)
0.25 (0.0098)
0.17 (0.0067)
COPLANARITY
0.10
45°
Figure 56. 14-Lead Standard Small Outline Package [SOIC_N]
Narrow Body (R-14)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model1 Temperature Range Package Description Package Option Branding
AD8276ARMZ −40°C to +85°C 8-Lead MSOP RM-8 H1P
AD8276ARMZ-R7 −40°C to +85°C 8-Lead MSOP, 7" Tape and Reel RM-8 H1P
AD8276ARMZ-RL −40°C to +85°C 8-Lead MSOP, 13" Tape and Reel RM-8 H1P
AD8276ARZ −40°C to +85°C 8-Lead SOIC_N R-8
AD8276ARZ-R7 −40°C to +85°C 8-Lead SOIC_N, 7" Tape and Reel R-8
AD8276ARZ-RL −40°C to +85°C 8-Lead SOIC_N, 13" Tape and Reel R-8
AD8276BRMZ
−40°C to +85°C
8-Lead MSOP
RM-8
H1Q
AD8276BRMZ-R7 −40°C to +85°C 8-Lead MSOP, 7" Tape and Reel RM-8 H1Q
AD8276BRMZ-RL −40°C to +85°C 8-Lead MSOP, 13" Tape and Reel RM-8 H1Q
AD8276BRZ −40°C to +85°C 8-Lead SOIC_N R-8
AD8276BRZ-R7 −40°C to +85°C 8-Lead SOIC_N, 7" Tape and Reel R-8
AD8276BRZ-RL −40°C to +85°C 8-Lead SOIC_N, 13" Tape and Reel R-8
AD8277ARZ −40°C to +85°C 14-Lead SOIC_N R-14
AD8277ARZ-R7 −40°C to +85°C 14-Lead SOIC_N, 7" Tape and Reel R-14
AD8277ARZ-RL −40°C to +85°C 14-Lead SOIC_N, 13" Tape and Reel R-14
AD8277BRZ −40°C to +85°C 14-Lead SOIC_N R-14
AD8277BRZ-R7 −40°C to +85°C 14-Lead SOIC_N, 7" Tape and Reel R-14
AD8277BRZ-RL −40°C to +85°C 14-Lead SOIC_N, 13" Tape and Reel R-14
1 Z = RoHS Compliant Part.
©20092011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D07692-0-11/11(C)

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