AD8276BRZ [ADI]
Low Power, Wide Supply Range, Low Cost Unity-Gain Difference Amplifiers; 低功耗，宽电源电压范围，低成本单位增益差分放大器
| 型号： | AD8276BRZ |
| 厂家： | 
ADI |
| 描述： | Low Power, Wide Supply Range, Low Cost Unity-Gain Difference Amplifiers |
| 文件： | 总20页 (文件大小：537K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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
7
AD8276
40kΩ
40kΩ
2
5
6
–IN
+IN
SENSE
OUT
40kΩ
40kΩ
3
1
REF
4
Wide power supply range:
–VS
Single supply: 2 V to 36 V
Dual supplies: 2 V to 18 V
Figure 1. AD8276
+VS
11
APPLICATIONS
AD8277
40kΩ
40kΩ
Voltage measurement and monitoring
Current measurement and monitoring
Differential output instrumentation amplifier
Portable, battery-powered equipment
Test and measurement
2
12
13
–INA
SENSEA
OUTA
40kΩ
40kΩ
40kΩ
40kΩ
3
6
14
+INA
–INB
REFA
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.
10
9
SENSEB
OUTB
40kΩ
40kΩ
5
8
+INB
REFB
4
–VS
Figure 2. AD8277
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.
Table 1. Difference Amplifiers by Category
Low
Distortion
High
Voltage
Current
Sensing1
Low Power
AD8276
AD8277
AD8270
AD8271
AD8273
AD8274
AMP03
AD628
AD629
AD8202 (U)
AD8203 (U)
AD8205 (B)
AD8206 (B)
AD8216 (B)
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.
AD8278
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.
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.
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 registeredtrademarks arethe 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
©2009 Analog Devices, Inc. All rights reserved.
AD8276/AD8277
TABLE OF CONTENTS
Features .............................................................................................. 1
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
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
REVISION HISTORY
7/09—Rev. 0 to Rev. A
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
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
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
Grade B
Typ
Grade A
Typ Max
Parameter
Conditions
Min
Max
Min
Unit
INPUT CHARACTERISTICS
System Offset1
100
0.5
200
200
100 500
500
μV
μV
vs. Temperature
Average Temperature
Coefficient
TA = −40°C to +85°C
TA = −40°C to +85°C
VS = 5 V to 18 V
2
5
2
5
μV/°C
μV/V
vs. Power Supply
10
Common-Mode Rejection
Ratio (RTI)
Input Voltage Range2
Impedance3
VS = 15 V, VCM = 2ꢀ V,
RS = 0 Ω
86
80
dB
V
−2(VS + 0.1)
+2(VS − 1.5) −2(VS + 0.1)
+2(VS − 1.5)
Differential
80
40
80
40
kΩ
kΩ
Common Mode
DYNAMIC PERFORMANCE
Bandwidth
550
1.1
550
1.1
kHz
V/μs
Slew Rate
0.9
0.9
Settling Time to 0.01%
10 V step on output,
CL = 100 pF
15
16
15
16
μs
μs
dB
Settling Time to 0.001%
Channel Separation
GAIN
f = 1 kHz
130
130
Gain Error
0.005 0.02
0.01 0.05
%
Gain Drift
TA = −40°C to +85°C
VOUT = 20 V p-p
1
5
5
10
ppm/°C
ppm
Gain Nonlinearity
OUTPUT CHARACTERISTICS
Output Voltage Swing4
VS = 15 V, RL = 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
Capacitive Load Drive
NOISE5
15
200
15
200
mA
pF
Output Voltage Noise
f = 0.1 Hz to 10 Hz
f = 1 kHz
2
65
2
65
ꢁV p-p
nV/√Hz
ꢀ0
ꢀ0
POWER SUPPLY
Supply Current6
vs. Temperature
Operating Voltage Rangeꢀ
TEMPERATURE RANGE
Operating Range
200
250
18
200
250
18
ꢁA
ꢁA
V
TA = −40°C to +85°C
2
2
−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.
ꢀ 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.
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
Grade B
Typ
Grade A
Typ Max
Parameter
Conditions
Min
Max
Min
Unit
INPUT CHARACTERISTICS
System Offset1
100
0.5
200
200
100 500
500
μV
μV
vs. Temperature
Average Temperature
Coefficient
TA = −40°C to +85°C
TA = −40°C to +85°C
VS = 5 V to 18 V
2
5
2
5
μV/°C
μV/V
vs. Power Supply
10
Common-Mode Rejection VS = 2.ꢀ V, VCM = 0 V
Ratio (RTI)
to 2.4 V, RS = 0 Ω
86
80
80
dB
VS = 5 V, VCM = −10 V
to +ꢀ V, RS = 0 Ω
86
dB
V
Input Voltage Range2
Impedance3
−2(VS + 0.1)
+2(VS − 1.5) −2(VS + 0.1)
+2(VS − 1.5)
Differential
80
40
80
40
kΩ
kΩ
Common Mode
DYNAMIC PERFORMANCE
Bandwidth
450
1.0
450
1.0
kHz
V/μs
Slew Rate
Settling Time to 0.01%
8 V step on output,
CL = 100 pF, VS = 10 V
5
5
μs
Channel Separation
GAIN
f = 1 kHz
130
130
dB
Gain Error
Gain Drift
0.005
0.02
1
0.01 0.05
5
%
TA = −40°C to +85°C
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
NOISE5
200
200
pF
Output Voltage Noise
f = 0.1 Hz to 10 Hz
f = 1 kHz
2
65
2
65
ꢁV p-p
nV/√Hz
POWER SUPPLY
Supply Current6
Operating Voltage
Range
TA = −40°C to +85°C
200
36
200
36
ꢁA
V
2.0
2.0
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.
Rev. A | Page 4 of 20
AD8276/AD8277
ABSOLUTE MAXIMUM RATINGS
Table 4.
2.0
1.6
1.2
0.8
0.4
0
T
MAX = 150°C
J
Parameter
Rating
14-LEAD SOIC
= 105°C/W
Supply Voltage
18 V
θ
JA
Maximum Voltage at Any Input Pin
Minimum Voltage at Any Input Pin
Storage Temperature Range
Specified Temperature Range
Package Glass Transition Temperature (TG)
−VS + 40 V
+VS − 40 V
−65°C to +150°C
−40°C to +85°C
150°C
8-LEAD SOIC
= 121°C/W
θ
JA
8-LEAD MSOP
= 135°C/W
θ
JA
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.
–50
–25
0
25
50
75
100
125
AMBIENT TEMERATURE (°C)
Figure 3. Maximum Power Dissipation vs. Ambient Temperature
SHORT-CIRCUIT CURRENT
THERMAL RESISTANCE
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.
Table 5.
Package Type
8-Lead MSOP
8-Lead SOIC
θJA
Unit
°C/W
°C/W
°C/W
135
121
105
14-Lead SOIC
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
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
REF
1
2
3
4
8
7
6
5
NC
REF
–IN
1
2
3
4
8
7
6
5
NC
AD8276
TOP VIEW
AD8276
TOP VIEW
(Not to Scale)
–IN
+VS
+VS
+IN
–VS
OUT
SENSE
+IN
OUT
SENSE
(Not to Scale)
–VS
NC = NO CONNECT
NC = NO CONNECT
Figure 4. AD8276 8-Lead MSOP Pin Configuration
Figure 5. AD8276 8-Lead SOIC Pin Configuration
Table 6. AD8276 Pin Function Descriptions
Pin No.
Mnemonic Description
1
2
3
4
5
6
ꢀ
8
REF
−IN
+IN
−VS
SENSE
OUT
+VS
NC
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
–INA
+INA
–VS
1
2
3
4
5
6
7
14 REFA
13 OUTA
12 SENSEA
11 +VS
AD8277
TOP VIEW
(Not to Scale)
+INB
–INB
NC
10 SENSEB
9
8
OUTB
REFB
NC = NO CONNECT
Figure 6. AD8277 14-Lead SOIC Pin Configuration
Table 7. AD8277 Pin Function Descriptions
Pin No.
Mnemonic Description
1
NC
No Connect.
2
3
4
−INA
+INA
−VS
Channel A Inverting Input.
Channel A Noninverting Input.
Negative Supply.
5
6
ꢀ
+INB
−INB
NC
Channel B Noninverting Input.
Channel B Inverting Input.
No Connect.
8
9
REFB
OUTB
SENSEB
+VS
SENSEA
OUTA
REFA
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.
10
11
12
13
14
Rev. A | Page ꢀ of 20
AD8276/AD8277
TYPICAL PERFORMANCE CHARACTERISTICS
VS = 15 V, TA = 25°C, RL = 10 kꢀ connected to ground, G = 1 difference amplifier configuration, unless otherwise noted.
80
N = 2042
MEAN = –2.28
600
500
400
300
200
100
0
SD = 32.7
60
40
20
0
–20
–40
–60
–80
–100
–300
–200
–100
0
100
200
300
–50
–35
–20
–5
10
25
40
55
70
85
SYSTEM OFFSET VOLTAGE (µV)
TEMPERATURE (°C)
Figure 7. Distribution of Typical System Offset Voltage
Figure 10. System Offset vs. Temperature, Normalized at 25°C
20
15
N = 2040
MEAN = –0.87
SD = 16.2
400
300
200
100
0
10
5
0
–5
–10
–15
–20
–25
REPRESENTATIVE DATA
–30
–50
–90
–60
–30
0
30
60
90
–35
–20
–5
10
25
40
55
70
85 90
CMRR (µV/V)
TEMPERATURE (°C)
Figure 11. Gain Error vs. Temperature, Normalized at 25°C
Figure 8. Distribution of Typical Common-Mode Rejection
10
4
0
–10
–20
–30
–40
–50
2
0
V
= ±15V
S
V
= +2.7V
–2
S
–4
–6
–8
REPRESENTATIVE DATA
100
1k
10k
100k
1M
10M
–50
–35
–20
–5
10
25
40
55
70
85 90
FREQUENCY (Hz)
TEMPERATURE (°C)
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
AD8276/AD8277
120
100
80
60
40
20
0
8
6
V
= ±15V
V
= MIDSUPPLY
S
REF
V
= 5V
S
4
2
0
V
= 2.7V
S
–2
–4
–6
1
10
100
1k
10k
100k
1M
–0.5
0.5
1.5
2.5
3.5
4.5
5.5
FREQUENCY (Hz)
OUTPUT VOLTAGE (V)
Figure 13. CMRR vs. Frequency
Figure 16. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = Midsupply
120
100
80
60
40
20
0
8
V
= 0V
REF
V
= 5V
S
6
4
–PSRR
2
+PSRR
V
= 2.7V
S
0
–2
–4
1
10
100
1k
10k
100k
1M
–0.5
0.5
1.5
2.5
3.5
4.5
5.5
FREQUENCY (Hz)
OUTPUT VOLTAGE (V)
Figure 14. PSRR vs. Frequency
Figure 17. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = 0 V
+V
S
30
20
–0.1
–0.2
–0.3
–0.4
V
= ±15V
S
10
T
T
T
T
= –40°C
= +25°C
= +85°C
= +125°C
A
A
A
A
V
= ±5V
S
0
+0.4
+0.3
+0.2
+0.1
–10
–20
–30
–V
S
2
4
6
8
10
12
14
16
18
–20
–15
–10
–5
0
5
10
15
20
SUPPLY VOLTAGE (±V )
OUTPUT VOLTAGE (V)
S
Figure 15. Input Common-Mode Voltage vs. Output Voltage,
15 V and 5 V Supplies
Figure 18. Output Voltage Swing vs. Supply Voltage Per Channel and
Temperature, RL = 10 kΩ
Rev. A | Page 9 of 20
AD8276/AD8277
+V
180
170
160
150
140
130
120
S
–0.2
–0.4
–0.6
–0.8
–1.0
–1.2
T
T
T
T
= –40°C
= +25°C
= +85°C
= +125°C
A
A
A
A
+1.2
+1.0
+0.8
+0.6
+0.4
+0.2
–V
S
2
4
6
8
10
12
14
16
18
0
2
4
6
8
10
12
14
16
18
SUPPLY VOLTAGE (±V )
SUPPLY VOLTAGE (±V)
S
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
170
160
150
140
130
120
+V
S
–4
–8
T
T
T
T
= –40°C
= +25°C
= +85°C
= +125°C
A
A
A
A
+8
+4
–V
S
1k
0
5
10
15
20
25
30
35
40
10k
100k
SUPPLY VOLTAGE (V)
LOAD RESISTANCE (Ω)
Figure 20. Output Voltage Swing vs. RL and Temperature, VS = 15 V
Figure 23. Supply Current Per Channel vs. Single-Supply Voltage, VIN = 0 V,
VREF = 0 V
+V
250
S
V
= MIDSUPPLY
REF
–0.5
–1.0
–1.5
–2.0
200
150
100
50
T
T
T
T
= –40°C
= +25°C
= +85°C
= +125°C
A
A
A
A
V
= ±15V
S
+2.0
+1.5
+1.0
+0.5
V
= +2.7V
S
–V
0
–50
S
–30
–10
10
30
50
70
90
110
130
0
1
2
3
4
5
6
7
8
9
10
OUTPUT CURRENT (mA)
TEMPERATURE (°C)
Figure 24. Supply Current Per Channel vs. Temperature
Figure 21. Output Voltage Swing vs. IOUT and Temperature, VS = 15 V
Rev. A | Page 10 of 20
AD8276/AD8277
30
25
20
15
10
5
5V/DIV
I
SHORT+
11.24 µs TO 0.01%
13.84µs TO 0.001%
0
0.002%/DIV
–5
–10
–15
–20
I
SHORT–
50
40µs/DIV
TIME (µs)
–50
–30
–10
10
30
70
90
110
130
TEMPERATURE (°C)
Figure 25. Short-Circuit Current Per Channel vs. Temperature
Figure 28. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = 15 V
1.4
1.2
–SR
1.0
1V/DIV
+SR
0.8
4.34 µs TO 0.01%
5.12µs TO 0.001%
0.6
0.4
0.2
0
0.002%/DIV
40µs/DIV
TIME (µs)
–50
–30
–10
10
30
50
70
90
110
130
TEMPERATURE (°C)
Figure 26. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz
Figure 29. Large-Signal Pulse Response and Settling Time, 2 V Step,
VS = 2.7 V
8
6
4
2
0
–2
–4
–6
–8
10µs/DIV
–10
–8
–6
–4
–2
0
2
4
6
8
10
OUTPUT VOLTAGE (V)
Figure 27. Gain Nonlinearity, VS = 15 V, RL ≥ 2 kΩ
Figure 30. Large-Signal Step Response
Rev. A | Page 11 of 20
AD8276/AD8277
30
40
35
30
25
20
15
10
5
V
= ±15V
S
25
20
15
10
5
±2V
±5V
±18V
±15V
V
= ±5V
S
0
100
0
100
1k
10k
100k
1M
150
200
250
300
350
400
FREQUENCY (Hz)
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
1k
V
= 5V
S
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
100
V
= 2.7V
S
10
0.1
100
1k
10k
100k
1M
1
10
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 32. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V
Figure 35. Voltage Noise Density vs. Frequency
C
= 100pF
L
C
= 200pF
L
C
= 300pF
L
C
= 470pF
L
40µs/DIV
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
AD8276/AD8277
160
140
120
100
80
NO LOAD
10kΩ LOAD
2kΩ LOAD
1kΩ LOAD
60
40
20
0
1
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 37. Channel Separation
Rev. A | Page 13 of 20
AD8276/AD8277
THEORY OF OPERATION
AC Performance
CIRCUIT INFORMATION
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.
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.
+VS
DRIVING THE AD8276/AD8277
7
AD8276
40kΩ
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 (kꢀ) 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.
40kΩ
2
5
6
IN–
IN+
SENSE
OUT
40kΩ
40kΩ
3
1
REF
4
–VS
INPUT VOLTAGE RANGE
Figure 38. Functional Block Diagram
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.
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
R1 + R2
R4
R3
R4
R3
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎜
⎝
⎞
⎟
⎠
VOUT = VIN +
1 +
− V
IN −
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.
R2
R1 + R2
(V
)
IN+
R4
R3
R1
V
V
IN–
IN+
The difference amplifier output voltage equation can be reduced to
R2
R4
R3
R2
R1 + R2
VOUT
=
(
VIN + − VI
)
(V
)
IN+
N −
Figure 39. Voltage Division in the Difference Amplifier Configuration
as long as the following ratio of the resistors is tightly matched:
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.
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.
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 are typically specified at single- and dual-
supplies, 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.
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:
R1
R1 + R2
(V
)
REF
R4
R3
R1
R2
V
R1
R1 + R2
REF
R1
R1 + R2
VREF < +VS −1.5 V
(V
REF
)
Figure 40. Ensure Sufficient Voltage Headroom on the Internal Op Amp
Inputs
For example, when operating on a +VS = 2 V single supply and
V
REF = 0 V, it can be seen from Figure 40 that the input terminals
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.
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.
Rev. A | Page 15 of 20
AD8276/AD8277
APPLICATIONS INFORMATION
CONFIGURATIONS
40kΩ
40kΩ
2
5
6
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.
OUT
40kΩ
40kΩ
1
3
V
= –V
IN
OUT
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
40kΩ
40kΩ
40kΩ
2
5
6
OUT
1
3
INCORRECT
CORRECT
IN
V
= V
OUT
IN
Figure 45. Noninverting Amplifier, Gain = 1
AD8276
AD8276
REF
REF
V
V
40kΩ
40kΩ
2
5
6
+
OP1177
–
OUT
40kΩ
40kΩ
1
3
IN
Figure 41. Driving the Reference Pin
V
= 2V
OUT
IN
Figure 46. Noninverting Amplifier, Gain = 2
40kΩ
40kΩ
40kΩ
40kΩ
2
5
6
–IN
DIFFERENTIAL OUTPUT
OUT
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.
3
1
+IN
V
= V
− V
OUT
IN+ IN−
Figure 42. Difference Amplifier, Gain = 1
40kΩ
40kΩ
40kΩ
40kΩ
2
5
6
–IN
OUT
3
1
+IN
V
= MIDSUPPLY
REF
V
= V
− V
OUT
IN+ IN−
V
+
AD8226
S
+IN
–IN
Figure 43. Difference Amplifier, Gain = 1, Referenced to Midsupply
+OUT
V
REF
R
R
R
AD8276
R
V
= V
CM
BIAS
–OUT
V –
S
Figure 47. Differential Output With Supply Tracking on Common-Mode
Voltage Reference
Rev. A | Page 16 of 20
AD8276/AD8277
V+
The differential output voltage and common-mode voltage of
the AD8226 is shown in the following equations:
V+
–2.5V
7
1
2
3
4
5
10
9
40kΩ
5
VDIFF_OUT = V+OUT − V−OUT = GainAD8226 × (V+IN – V−IN
VCM = (VS+ − VS−)/2 = VBIAS
)
40kΩ
40kΩ
2
8
R2
6
2N3904
3
7
REF
ADR821
Refer to the AD8226 data sheet for additional information.
R1
6
40kΩ
1
+VS
V–
R
AD8276
LOAD
11
4
AD8277
I
= 2.5V(1/40kΩ + 1/R1)
O
40kΩ
40kΩ
R1 = R2
2
–IN
+IN
12
13
Figure 49. Constant Current Source
+OUT
VOLTAGE AND CURRENT MONITORING
Voltage and current monitoring is critical in the following
40kΩ
40kΩ
40kΩ
40kΩ
3
6
14
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.
10
9
–OUT
40kΩ
40kΩ
5
8
AD8276
4
I
1
R
–VS
Figure 48. AD8277 Differential Output Configuration
AD8276
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:
I
3
R
I
C
ADC
OP1177
8:1
V
1
R
VDIFF_OUT = V+OUT − V−OUT = 2 × (V+IN – V−IN
)
AD8276
AD8276
CURRENT SOURCE
V
3
R
R
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.
V
C
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.
The AD8276 has rail-to-rail output capability that allows higher
current outputs.
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 1ꢀ of 20
AD8276/AD8277
resistor is determined by the characteristics of the coupler or
transformer and desired input voltage ranges to the AD8276.
Table 8. Low Power Op Amps
Op Amp (A1, A2) Features
AD8506
AD860ꢀ
AD861ꢀ
AD866ꢀ
Dual micropower op amp
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.
Precision dual micropower op amp
Low cost CMOS micropower op amp
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.
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.
Refer to A Designer’s Guide to Instrumentation Amplifiers for
more design ideas and considerations.
I
SH
AD8276
R
RTD
SH
V
= I × R
SH SH
OUT
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.
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
I
EX
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
L1
V
R
OUT
T
Σ-Δ
ADC
R
R
L2
L3
AD8276
REF
–IN
A1
40kΩ
Figure 53. 3-Wire RTD Cable Resistance Error Measurement
R
F
40kΩ
40kΩ
R
G
V
OUT
40kΩ
AD8276
R
F
REF
= (1 + 2R /R ) (V
IN+
A2
+IN
V
– V )
IN–
OUT
F
G
Figure 52. Low Power Precision Instrumentation Amplifier
Rev. A | Page 18 of 20
AD8276/AD8277
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 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
6.20 (0.2441)
5.80 (0.2284)
4.00 (0.1574)
3.80 (0.1497)
0.50 (0.0196)
0.25 (0.0099)
1.27 (0.0500)
BSC
45°
1.75 (0.0688)
1.35 (0.0532)
0.25 (0.0098)
0.10 (0.0040)
8°
0°
0.51 (0.0201)
0.31 (0.0122)
COPLANARITY
0.10
1.27 (0.0500)
0.40 (0.0157)
0.25 (0.0098)
0.17 (0.0067)
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS MS-012-AA
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
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
AD82ꢀ6ARZ1
Temperature Range
Package Description
Package Option
R-8
Branding
−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
8-Lead SOIC_N
AD82ꢀ6ARZ-Rꢀ1
AD82ꢀ6ARZ-RL1
AD82ꢀ6BRZ1
8-Lead SOIC_N, ꢀ" Tape and Reel
8-Lead SOIC_N, 13" Tape and Reel
8-Lead SOIC_N
8-Lead SOIC_N, ꢀ" Tape and Reel
8-Lead SOIC_N, 13" Tape and Reel
8-Lead MSOP
8-Lead MSOP, ꢀ" Tape and Reel
8-Lead MSOP, 13" Tape and Reel
8-Lead MSOP
8-Lead MSOP, ꢀ" Tape and Reel
8-Lead MSOP, 13" Tape and Reel
14-Lead SOIC_N
14-Lead SOIC_N, ꢀ" Tape and Reel
14-Lead SOIC_N, 13" Tape and Reel
14-Lead SOIC_N
14-Lead SOIC_N, ꢀ" Tape and Reel
14-Lead SOIC_N, ꢀ" Tape and Reel
R-8
R-8
R-8
R-8
AD82ꢀ6BRZ-Rꢀ1
AD82ꢀ6BRZ-RL1
AD82ꢀ6ARMZ1
AD82ꢀ6ARMZ-Rꢀ1
AD82ꢀ6ARMZ-RL1
AD82ꢀ6BRMZ1
AD82ꢀ6BRMZ-Rꢀ1
AD82ꢀ6BRMZ-RL1
AD82ꢀꢀARZ1
AD82ꢀꢀARZ-Rꢀ1
AD82ꢀꢀARZ-RL1
AD82ꢀꢀBRZ1
AD82ꢀꢀBRZ-Rꢀ1
AD82ꢀꢀBRZ-RL1
R-8
RM-8
RM-8
RM-8
RM-8
RM-8
RM-8
R-14
R-14
R-14
R-14
R-14
H1P
H1P
H1P
H1Q
H1Q
H1Q
R-14
1 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
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