AD AD8277BRZ Low power, wide supply range, low cost unity-gain difference amplifier Datasheet

Low Power, Wide Supply Range, Low Cost
Unity-Gain Difference Amplifiers
AD8276/AD8277
FEATURES
FUNCTIONAL BLOCK DIAGRAM
+VS
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
7
AD8276
+IN 3
40kΩ
40kΩ
40kΩ
5
SENSE
6
OUT
1
REF
12
SENSEA
13
OUTA
14
REFA
10
SENSEB
9
OUTB
8
REFB
07692-001
–IN 2
40kΩ
4
–VS
Figure 1. AD8276
+VS
11
APPLICATIONS
AD8277
Voltage measurement and monitoring
Current measurement and monitoring
Differential output instrumentation amplifier
Portable, battery-powered equipment
Test and measurement
–INA 2
+INA 3
40kΩ
40kΩ
40kΩ
40kΩ
40kΩ
40kΩ
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 singlesupply 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 batteryoperated and portable systems.
–INB 6
+INB 5
40kΩ
40kΩ
4
–VS
07692-052
GENERAL DESCRIPTION
Figure 2. AD8277
Table 1. Difference Amplifiers by Category
Low
Distortion
AD8270
AD8271
AD8273
AD8274
AMP03
1
High
Voltage
AD628
AD629
Current
Sensing1
AD8202 (U)
AD8203 (U)
AD8205 (B)
AD8206 (B)
AD8216 (B)
Low Power
AD8276
AD8277
AD8278
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.
Rev. A
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 Analog Devices, Inc. All rights reserved.
AD8276/AD8277
TABLE OF CONTENTS
Features .............................................................................................. 1
Circuit Information.................................................................... 14
Applications ....................................................................................... 1
Driving the AD8276/AD8277 .................................................. 14
General Description ......................................................................... 1
Input Voltage Range ................................................................... 14
Functional Block Diagram .............................................................. 1
Power Supplies ............................................................................ 15
Revision History ............................................................................... 2
Applications Information .............................................................. 16
Specifications..................................................................................... 3
Configurations ............................................................................ 16
Absolute Maximum Ratings............................................................ 5
Differential Output .................................................................... 16
Thermal Resistance ...................................................................... 5
Current Source............................................................................ 17
Maximum Power Dissipation ..................................................... 5
Voltage and Current Monitoring.............................................. 17
Short-Circuit Current .................................................................. 5
Instrumentation Amplifier........................................................ 18
ESD Caution .................................................................................. 5
RTD .............................................................................................. 18
Pin Configurations and Function Descriptions ........................... 6
Outline Dimensions ....................................................................... 19
Typical Performance Characteristics ............................................. 8
Ordering Guide .......................................................................... 20
Theory of Operation ...................................................................... 14
REVISION HISTORY
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
Rev. A | Page 2 of 20
AD8276/AD8277
SPECIFICATIONS
VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 kΩ connected to ground, G = 1 difference amplifier configuration, unless
otherwise noted.
Table 2.
G=1
Parameter
INPUT CHARACTERISTICS
System Offset 1
vs. Temperature
Average Temperature
Coefficient
vs. Power Supply
Common-Mode Rejection
Ratio (RTI)
Input Voltage Range 2
Impedance 3
Differential
Common Mode
DYNAMIC PERFORMANCE
Bandwidth
Slew Rate
Settling Time to 0.01%
Settling Time to 0.001%
Channel Separation
GAIN
Gain Error
Gain Drift
Gain Nonlinearity
OUTPUT CHARACTERISTICS
Output Voltage Swing 4
Short-Circuit Current Limit
Capacitive Load Drive
NOISE 5
Output Voltage Noise
POWER SUPPLY
Supply Current 6
vs. Temperature
Operating Voltage Range 7
TEMPERATURE RANGE
Operating Range
Conditions
Min
Grade B
Typ
Max
100
500
500
μV
μV
0.5
2
5
2
5
10
μV/°C
μV/V
+2(VS − 1.5)
dB
V
+2(VS − 1.5)
80
−2(VS + 0.1)
80
40
550
1.1
10 V step on output,
CL = 100 pF
130
0.005
TA = −40°C to +85°C
VOUT = 20 V p-p
VS = ±15 V, RL = 10 kΩ,
TA = −40°C to +85°C
0.9
80
40
kΩ
kΩ
550
1.1
kHz
V/μs
15
16
f = 1 kHz
−VS + 0.2
0.02
1
5
+VS − 0.2
2
65
15
16
μs
μs
dB
0.05
5
10
%
ppm/°C
ppm
+VS − 0.2
V
mA
pF
130
0.01
−VS + 0.2
±15
200
f = 0.1 Hz to 10 Hz
f = 1 kHz
Unit
200
200
86
−2(VS + 0.1)
0.9
Grade A
Typ Max
100
TA = −40°C to +85°C
TA = −40°C to +85°C
VS = ±5 V to ±18 V
VS = ±15 V, VCM = ±27 V,
RS = 0 Ω
Min
±15
200
2
65
70
70
μV p-p
nV/√Hz
μA
μA
V
°C
±2
200
250
±18
±2
200
250
±18
−40
+125
−40
+125
TA = −40°C to +85°C
1
Includes input bias and offset current errors, RTO (referred to output).
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.
2
Rev. A | Page 3 of 20
AD8276/AD8277
VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 kΩ connected to midsupply, G = 1 difference amplifier configuration, unless
otherwise noted.
Table 3.
G=1
Parameter
INPUT CHARACTERISTICS
System Offset 1
vs. Temperature
Average Temperature
Coefficient
vs. Power Supply
Common-Mode Rejection
Ratio (RTI)
Input Voltage Range 2
Impedance 3
Differential
Common Mode
DYNAMIC PERFORMANCE
Bandwidth
Slew Rate
Settling Time to 0.01%
Channel Separation
GAIN
Gain Error
Gain Drift
OUTPUT CHARACTERISTICS
Output Swing 4
Short-Circuit Current
Limit
Capacitive Load Drive
NOISE 5
Output Voltage Noise
POWER SUPPLY
Supply Current 6
Operating Voltage
Range
TEMPERATURE RANGE
Operating Range
Conditions
Grade B
Typ
Min
Unit
100
500
500
μV
μV
0.5
2
5
2
5
10
μV/°C
μV/V
80
86
−2(VS + 0.1)
+2(VS − 1.5)
dB
80
−2(VS + 0.1)
+2(VS − 1.5)
dB
V
80
40
80
40
kΩ
kΩ
450
1.0
450
1.0
kHz
V/μs
5
130
5
130
μs
dB
0.005
TA = −40°C to +85°C
−VS + 0.1
f = 0.1 Hz to 10 Hz
f = 1 kHz
Grade A
Typ Max
200
200
86
8 V step on output,
CL = 100 pF, VS = 10 V
f = 1 kHz
RL = 10 kΩ ,
TA = −40°C to +85°C
Min
100
TA = −40°C to +85°C
TA = −40°C to +85°C
VS = ±5 V to ±18 V
VS = 2.7 V, VCM = 0 V
to 2.4 V, RS = 0 Ω
VS = ±5 V, VCM = −10 V
to +7 V, RS = 0 Ω
Max
0.02
1
+VS − 0.15
0.01
%
ppm/°C
+VS − 0.15
±10
±10
V
mA
200
200
pF
2
65
2
65
μV p-p
nV/√Hz
TA = −40°C to +85°C
−VS + 0.1
0.05
5
2.0
200
36
2.0
200
36
μA
V
−40
+125
−40
+125
°C
1
Includes input bias and offset current errors, RTO (referred to output).
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.
2
Rev. A | Page 4 of 20
AD8276/AD8277
ABSOLUTE MAXIMUM RATINGS
2.0
Table 4.
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
Table 5.
θJA
135
121
105
14-LEAD SOIC
θJA = 105°C/W
1.2
8-LEAD SOIC
θJA = 121°C/W
0.8
8-LEAD MSOP
θJA = 135°C/W
0.4
0
–50
–25
0
25
50
75
100
125
AMBIENT TEMERATURE (°C)
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.
The θJA values in Table 5 assume a 4-layer JEDEC standard
board with zero airflow.
Package Type
8-Lead MSOP
8-Lead SOIC
14-Lead SOIC
1.6
07692-002
Rating
±18 V
−VS + 40 V
+VS − 40 V
−65°C to +150°C
−40°C to +85°C
150°C
MAXIMUM POWER DISSIPATION (W)
TJ MAX = 150°C
Parameter
Supply Voltage
Maximum Voltage at Any Input Pin
Minimum Voltage at Any Input Pin
Storage Temperature Range
Specified Temperature Range
Package Glass Transition Temperature (TG)
Unit
°C/W
°C/W
°C/W
ESD CAUTION
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.
Rev. A | Page 5 of 20
AD8276/AD8277
–IN 2
+IN 3
8
AD8276
NC
REF 1
7
TOP VIEW
(Not to Scale)
+VS
–IN 2
6
OUT
5
SENSE
–VS 4
NC = NO CONNECT
NC
7
+VS
6
OUT
5
SENSE
Figure 5. AD8276 8-Lead SOIC Pin Configuration
Table 6. AD8276 Pin Function Descriptions
Mnemonic
REF
−IN
+IN
−VS
SENSE
OUT
+VS
NC
8
NC = NO CONNECT
Figure 4. AD8276 8-Lead MSOP Pin Configuration
Pin No.
1
2
3
4
5
6
7
8
AD8276
TOP VIEW
+IN 3 (Not to Scale)
–VS 4
07692-003
REF 1
07692-004
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
Description
Reference Voltage Input.
Inverting Input.
Noninverting Input.
Negative Supply.
Sense Terminal.
Output.
Positive Supply.
No Connect.
Rev. A | Page 6 of 20
AD8276/AD8277
NC 1
14 REFA
–INA 2
13 OUTA
AD8277
+INA 3
12 SENSEA
TOP VIEW
11 +VS
(Not to Scale)
+INB 5
10 SENSEB
–INB 6
9
OUTB
NC 7
8
REFB
NC = NO CONNECT
07692-053
–VS 4
Figure 6. AD8277 14-Lead SOIC Pin Configuration
Table 7. AD8277 Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Mnemonic
NC
−INA
+INA
−VS
+INB
−INB
NC
REFB
OUTB
SENSEB
+VS
SENSEA
OUTA
REFA
Description
No Connect.
Channel A Inverting Input.
Channel A Noninverting Input.
Negative Supply.
Channel B Noninverting Input.
Channel B Inverting Input.
No Connect.
Channel B Reference Voltage Input.
Channel B Output.
Channel B Sense Terminal.
Positive Supply.
Channel A Sense Terminal.
Channel A Output.
Channel A Reference Voltage Input.
Rev. A | Page 7 of 20
AD8276/AD8277
TYPICAL PERFORMANCE CHARACTERISTICS
VS = ±15 V, TA = 25°C, RL = 10 kΩ connected to ground, G = 1 difference amplifier configuration, unless otherwise noted.
600
80
N = 2042
MEAN = –2.28
SD = 32.7
60
40
SYSTEM OFFSET (µV)
NUMBER OF HITS
500
400
300
200
20
0
–20
–40
–60
100
–200
–100
0
100
200
300
SYSTEM OFFSET VOLTAGE (µV)
–100
–50
07692-005
0
–300
–20
–5
10
25
40
55
70
85
TEMPERATURE (°C)
Figure 10. System Offset vs. Temperature, Normalized at 25°C
Figure 7. Distribution of Typical System Offset Voltage
400
–35
07692-008
–80
20
N = 2040
MEAN = –0.87
SD = 16.2
15
300
GAIN ERROR (µV/V)
NUMBER OF HITS
10
200
100
5
0
–5
–10
–15
–20
–30
0
30
60
90
CMRR (µV/V)
REPRESENTATIVE DATA
–30
–50
–35
–20
–5
10
07692-006
–60
40
55
70
85 90
Figure 11. Gain Error vs. Temperature, Normalized at 25°C
Figure 8. Distribution of Typical Common-Mode Rejection
4
10
2
0
0
–10
–2
–20
–4
–30
–6
–40
REPRESENTATIVE DATA
–8
–50
–35
–20
–5
10
25
40
55
70
TEMPERATURE (°C)
85 90
–50
100
VS = +2.7V
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 12. Gain vs. Frequency, VS = ±15 V, +2.7 V
Figure 9. CMRR vs. Temperature, Normalized at 25°C
Rev. A | Page 8 of 20
10M
07692-010
GAIN (dB)
VS = ±15V
07692-007
CMRR (µV/V)
25
TEMPERATURE (°C)
07692-009
–25
0
–90
AD8276/AD8277
120
8
VS = ±15V
COMMON-MODE VOLTAGE (V)
100
60
40
20
100
1k
10k
100k
1M
VS = 2.7V
–2
–6
–0.5
0.5
1.5
2.5
3.5
4.5
5.5
OUTPUT VOLTAGE (V)
Figure 16. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = Midsupply
120
8
COMMON-MODE VOLTAGE (V)
100
80
–PSRR
60
+PSRR
40
20
VREF = 0V
VS = 5V
6
4
2
VS = 2.7V
0
–2
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
–4
–0.5
07692-012
1
0.5
1.5
2.5
3.5
4.5
5.5
OUTPUT VOLTAGE (V)
Figure 14. PSRR vs. Frequency
07692-015
PSRR (dB)
0
07692-014
10
07692-011
1
Figure 13. CMRR vs. Frequency
Figure 17. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = 0 V
+VS
30
–0.1
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
VS = ±15V
20
10
VS = ±5V
0
–10
–20
–0.2
–0.3
–0.4
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
+0.4
+0.3
+0.2
+0.1
–30
–20
–15
–10
–5
0
5
10
15
20
OUTPUT VOLTAGE (V)
07692-013
COMMON-MODE VOLTAGE (V)
2
–4
FREQUENCY (Hz)
0
VS = 5V
4
Figure 15. Input Common-Mode Voltage vs. Output Voltage,
±15 V and ±5 V Supplies
–VS
2
4
6
8
10
12
SUPPLY VOLTAGE (±VS)
14
16
18
07692-016
CMRR (dB)
80
0
VREF = MIDSUPPLY
6
Figure 18. Output Voltage Swing vs. Supply Voltage Per Channel and
Temperature, RL = 10 kΩ
Rev. A | Page 9 of 20
AD8276/AD8277
180
+VS
–0.4
170
–0.6
SUPPLY CURRENT (µA)
–0.8
–1.0
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
–1.2
+1.2
+1.0
+0.8
+0.6
2
4
6
8
10
12
14
16
18
SUPPLY VOLTAGE (±VS)
140
120
0
2
4
6
8
10
12
14
16
18
SUPPLY VOLTAGE (±V)
Figure 22. Supply Current Per Channel vs. Dual Supply Voltage, VIN = 0 V
Figure 19. Output Voltage Swing vs. Supply Voltage Per Channel and
Temperature, RL = 2 kΩ
180
–4
170
SUPPLY CURRENT (µA)
+VS
–8
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
+8
160
150
140
–VS
1k
10k
100k
120
LOAD RESISTANCE (Ω)
0
5
10
15
20
25
30
35
40
SUPPLY VOLTAGE (V)
07692-021
130
+4
07692-018
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
150
07692-020
+0.2
–VS
160
130
+0.4
07692-017
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
–0.2
Figure 23. Supply Current Per Channel vs. Single-Supply Voltage, VIN = 0 V,
VREF = 0 V
Figure 20. Output Voltage Swing vs. RL and Temperature, VS = ±15 V
250
+VS
VREF = MIDSUPPLY
200
–1.0
SUPPLY CURRENT (µA)
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
–0.5
–1.5
–2.0
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
+2.0
+1.5
150
VS = ±15V
100
VS = +2.7V
50
+1.0
0
1
2
3
4
5
6
7
8
9
10
OUTPUT CURRENT (mA)
Figure 21. Output Voltage Swing vs. IOUT and Temperature, VS = ±15 V
Rev. A | Page 10 of 20
0
–50
–30
–10
10
30
50
70
90
110
TEMPERATURE (°C)
Figure 24. Supply Current Per Channel vs. Temperature
130
07692-022
–VS
07692-019
+0.5
AD8276/AD8277
30
20
15
5V/DIV
ISHORT+
10
11.24 µs TO 0.01%
13.84µs TO 0.001%
5
0
0.002%/DIV
–5
–10
ISHORT–
–15
40µs/DIV
–30
–10
10
30
50
70
90
110
130
TEMPERATURE (°C)
TIME (µs)
07692-023
–20
–50
Figure 25. Short-Circuit Current Per Channel vs. Temperature
07692-026
SHORT-CIRCUIT CURRENT (mA)
25
Figure 28. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = ±15 V
1.4
1.2
–SR
SLEW RATE (V/µs)
1.0
1V/DIV
+SR
0.8
4.34 µs TO 0.01%
5.12µs TO 0.001%
0.6
0.002%/DIV
0.4
40µs/DIV
–30
–10
10
30
50
70
90
110
130
TEMPERATURE (°C)
TIME (µs)
07692-024
0
–50
Figure 26. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz
07692-027
0.2
Figure 29. Large-Signal Pulse Response and Settling Time, 2 V Step,
VS = 2.7 V
8
4
2V/DIV
2
0
–2
–4
–8
–10
–8
–6
–4
–2
0
2
4
6
8
OUTPUT VOLTAGE (V)
10
Figure 27. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ
10µs/DIV
Figure 30. Large-Signal Step Response
Rev. A | Page 11 of 20
07692-028
–6
07692-025
NONLINEARITY (2ppm/DIV)
6
AD8276/AD8277
30
40
VS = ±15V
35
25
±2V
OUTPUT VOLTAGE (V p-p)
30
OVERSHOOT (%)
20
15
10
VS = ±5V
±5V
25
20
±18V
±15V
15
10
5
1k
10k
100k
1M
FREQUENCY (Hz)
0
100
07692-029
0
100
200
250
300
350
400
CAPACITIVE LOAD (pF)
Figure 31. Maximum Output Voltage vs. Frequency, VS = ±15 V, ±5 V
Figure 34. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ
5.0
4.5
150
07692-051
5
1k
VS = 5V
3.5
NOISE (nV/ Hz)
OUTPUT VOLTAGE (V p-p)
4.0
3.0
2.5
VS = 2.7V
2.0
100
1.5
1.0
1k
10k
100k
1M
FREQUENCY (Hz)
10
0.1
1
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 35. Voltage Noise Density vs. Frequency
1µV/DIV
20mV/DIV
Figure 32. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V
CL = 100pF
CL = 200pF
1s/DIV
Figure 33. Small-Signal Step Response for Various Capacitive Loads
Figure 36. 0.1 Hz to 10 Hz Voltage Noise
Rev. A | Page 12 of 20
07692-035
CL = 470pF
40µs/DIV
07692-050
CL = 300pF
07692-034
0
100
07692-030
0.5
AD8276/AD8277
160
NO LOAD
140
2kΩ LOAD
100
1kΩ LOAD
80
60
40
20
0
1
10
100
1k
FREQUENCY (Hz)
10k
100k
07692-055
CHANNEL SEPARATION (dB)
10kΩ LOAD
120
Figure 37. Channel Separation
Rev. A | Page 13 of 20
AD8276/AD8277
THEORY OF OPERATION
CIRCUIT INFORMATION
AC Performance
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.
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.
+VS
DRIVING THE AD8276/AD8277
7
AD8276
40kΩ
40kΩ
40kΩ
5
SENSE
6
OUT
1
REF
4
–VS
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
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
⎛ R2 ⎞⎛
⎟ 1 + R4 ⎞⎟ − V IN − ⎛⎜ R4 ⎞⎟
VOUT = V IN + ⎜
⎜ R1 + R2 ⎟⎜⎝
R3 ⎠
⎝ R3 ⎠
⎝
⎠
This equation demonstrates that the gain accuracy and commonmode 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 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.
R2 (V )
R1 + R2 IN+
R4
VIN–
VIN+
The difference amplifier output voltage equation can be reduced to
VOUT
R3
R1
R2
R4
(VIN + − VI N − )
=
R3
R2 (V )
R1 + R2 IN+
as long as the following ratio of the resistors is tightly matched:
R2 R4
=
R1 R3
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.
07692-033
IN+ 3
40kΩ
07692-031
IN–
2
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 +VS − 40 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.
Rev. A | Page 14 of 20
AD8276/AD8277
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:
The AD8276/AD8277 are typically specified at single- and dualsupplies, but they can be used with unbalanced supplies, as well;
for example, −VS = −5 V, +VS = 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.
R1 (V
)
R1 + R2 REF
R4
R3
R1
R2
R1
V REF < + VS − 1.5 V
R1 + R2
VREF
R1 (V
)
R1 + R2 REF
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 non inverting input. Therefore,
the user needs to increase the supply voltage or decrease VREF to
restore proper operation.
07692-032
POWER SUPPLIES
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.
Rev. A | Page 15 of 20
AD8276/AD8277
APPLICATIONS INFORMATION
CONFIGURATIONS
IN
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.
1
5
OUT
6
40kΩ
07692-040
3 40kΩ
VOUT = –VIN
Figure 44. Inverting Amplifier, Gain = −1
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.
40kΩ
2 40kΩ
5
OUT
6
CORRECT
IN
3 40kΩ
40kΩ
1
07692-041
INCORRECT
40kΩ
2 40kΩ
VOUT = VIN
AD8276
AD8276
REF
Figure 45. Noninverting Amplifier, Gain = 1
REF
V
V
2 40kΩ
+
40kΩ
OP1177
OUT
6
07692-037
1 40kΩ
IN
Figure 41. Driving the Reference Pin
3 40kΩ
07692-042
–
5
VOUT = 2VIN
Figure 46. Noninverting Amplifier, Gain = 2
2 40kΩ
40kΩ
5
6
3 40kΩ
40kΩ
1
07692-038
+IN
DIFFERENTIAL OUTPUT
OUT
VOUT = VIN+ − VIN−
Figure 42. Difference Amplifier, Gain = 1
2 40kΩ
40kΩ
5
6
+IN
3 40kΩ
VOUT = VIN+ − VIN−
40kΩ
OUT
1
VREF = MIDSUPPLY
07692-039
–IN
Certain systems require a differential signal for better performance, 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.
+IN
Figure 43. Difference Amplifier, Gain = 1, Referenced to Midsupply
–IN
AD8226
VREF
R
R
VS +
AD8276
+OUT
R
R
VS–
VBIAS = VCM
–OUT
07692-043
–IN
Figure 47. Differential Output With Supply Tracking on Common-Mode
Voltage Reference
Rev. A | Page 16 of 20
AD8276/AD8277
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+IN – V−IN)
VCM = (VS+ − VS−)/2 = VBIAS
Refer to the AD8226 data sheet for additional information.
V+
V+
1
10
2
9
3
8
4
7
5
+VS
REF
–2.5V
40kΩ
6
40kΩ
R1
1
RLOAD
4
07692-046
40kΩ
R2
2N3904
AD8276
AD8277
2
6
3 40kΩ
11
–IN
5
2 40kΩ
ADR821
V–
7
IO = 2.5V(1/40kΩ + 1/R1)
R1 = R2
40kΩ
12
Figure 49. Constant Current Source
13
3
6
40kΩ
40kΩ
40kΩ
40kΩ
10
9
5
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.
14
40kΩ
40kΩ
–OUT
8
4
–VS
AD8276
07692-056
+IN
VOLTAGE AND CURRENT MONITORING
+OUT
I1
R
Figure 48. AD8277 Differential Output Configuration
AD8276
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:
I3
R
IC
AD8276
V1
R
V3
R
VC
R
VDIFF_OUT = V+OUT − V−OUT = 2 × (V+IN – V−IN)
8:1
OP1177
ADC
AD8276
CURRENT SOURCE
The AD8276 has rail-to-rail output capability that allows higher
current outputs.
AD8276
07692-057
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 recommended to maintain performance. The ADR821 provides a
precision voltage reference and integrated op amp that also
reduces error in the signal chain.
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
Rev. A | Page 17 of 20
AD8276/AD8277
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 also 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 80 kΩ differential input impedance that the
AD8276 presents is high enough that it should not load the
input signals.
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 inamp 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.
RTD
07692-058
VOUT = ISH × RSH
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
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.
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.
IEX
RL1
VOUT
RT
Σ-Δ
ADC
RL2
AD8276
RL3
REF
–IN
A1
Figure 53. 3-Wire RTD Cable Resistance Error Measurement
40kΩ
RF
40kΩ
VOUT
40kΩ
RF
A2
40kΩ
AD8276
REF
VOUT = (1 + 2RF/RG) (VIN+ – VIN–)
07692-045
RG
+IN
Features
Dual micropower op amp
Precision dual micropower op amp
Low cost CMOS micropower op amp
Dual precision CMOS micropower op amp
Refer to A Designer’s Guide to Instrumentation Amplifiers for
more design ideas and considerations.
AD8276
RSH
Op Amp (A1, A2)
AD8506
AD8607
AD8617
AD8667
07692-059
ISH
Table 8. Low Power Op Amps
Figure 52. Low Power Precision Instrumentation Amplifier
Rev. A | Page 18 of 20
AD8276/AD8277
OUTLINE DIMENSIONS
3.20
3.00
2.80
8
3.20
3.00
2.80
5.15
4.90
4.65
5
1
4
PIN 1
0.65 BSC
0.95
0.85
0.75
1.10 MAX
0.15
0.00
0.38
0.22
COPLANARITY
0.10
0.80
0.60
0.40
8°
0°
0.23
0.08
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 54. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
5.00 (0.1968)
4.80 (0.1890)
8
1
5
4
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
COPLANARITY
0.10
SEATING
PLANE
6.20 (0.2441)
5.80 (0.2284)
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.31 (0.0122)
0.50 (0.0196)
0.25 (0.0099)
45°
8°
0°
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
COMPLIANT TO JEDEC STANDARDS MS-012-A A
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 55. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body (R-8)
Dimensions shown in millimeters and (inches)
Rev. A | Page 19 of 20
012407-A
4.00 (0.1574)
3.80 (0.1497)
AD8276/AD8277
Figure 56. 14-Lead Standard Small Outline Package [SOIC_N]
Narrow Body (R-14)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model
AD8276ARZ 1
AD8276ARZ-R71
AD8276ARZ-RL1
AD8276BRZ1
AD8276BRZ-R71
AD8276BRZ-RL1
AD8276ARMZ1
AD8276ARMZ-R71
AD8276ARMZ-RL1
AD8276BRMZ1
AD8276BRMZ-R71
AD8276BRMZ-RL1
AD8277ARZ1
AD8277ARZ-R71
AD8277ARZ-RL1
AD8277BRZ1
AD8277BRZ-R71
AD8277BRZ-RL1
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Package Description
8-Lead SOIC_N
8-Lead SOIC_N, 7" Tape and Reel
8-Lead SOIC_N, 13" Tape and Reel
8-Lead SOIC_N
8-Lead SOIC_N, 7" Tape and Reel
8-Lead SOIC_N, 13" Tape and Reel
8-Lead MSOP
8-Lead MSOP, 7" Tape and Reel
8-Lead MSOP, 13" Tape and Reel
8-Lead MSOP
8-Lead MSOP, 7" Tape and Reel
8-Lead MSOP, 13" Tape and Reel
14-Lead SOIC_N
14-Lead SOIC_N, 7" Tape and Reel
14-Lead SOIC_N, 13" Tape and Reel
14-Lead SOIC_N
14-Lead SOIC_N, 7" Tape and Reel
14-Lead SOIC_N, 7" Tape and Reel
Z = RoHS Compliant Part.
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D07692-0-7/09(A)
Rev. A | Page 20 of 20
Package Option
R-8
R-8
R-8
R-8
R-8
R-8
RM-8
RM-8
RM-8
RM-8
RM-8
RM-8
R-14
R-14
R-14
R-14
R-14
R-14
Branding
H1P
H1P
H1P
H1Q
H1Q
H1Q