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Low Power, Wide Supply Range,
Low Cost Difference Amplifiers, G = ½, 2
AD8278/AD8279
FEATURES
Wide input range beyond supplies
Rugged input overvoltage protection
Low supply current: 200 μA maximum (per amplifier)
Low power dissipation: 0.5 mW at V
S
= 2.5 V
Bandwidth: 1 MHz (G = ½)
CMRR: 80 dB minimum, dc to 20 kHz (G = ½, B Grade)
Low offset voltage drift: ±1 μV/°C maximum (B Grade)
Low gain drift: 1 ppm/°C maximum (B Grade)
Enhanced slew rate: 1.4 V/μs
Wide power supply range
Single supply: 2 V to 36 V
Dual supplies: ±2 V to ±18 V
8-lead SOIC, 14-lead SOIC, and 8-lead MSOP packages
FUNCTIONAL BLOCK DIAGRAMS
+VS
7
AD8278
–IN
2
40kΩ
20kΩ
5
SENSE
6
OUT
+IN
3
40kΩ
20kΩ
1
REF
08308-001
4
–VS
Figure 1. AD8278
+VS
11
APPLICATIONS
Voltage measurement and monitoring
Current measurement and monitoring
Instrumentation amplifier building block
Portable, battery-powered equipment
Test and measurement
–INA
2
AD8279
40kΩ
20kΩ
12
13
SENSEA
OUTA
REFA
+INA
3
40kΩ
40kΩ
20kΩ
20kΩ
14
–INB
6
10
9
SENSEB
OUTB
REFB
08308-058
GENERAL DESCRIPTION
The AD8278 and AD8279 are general-purpose difference
amplifiers intended for precision signal conditioning in power
critical applications that require both high performance and low
power. The AD8278 and AD8279 provide exceptional common-
mode rejection ratio (80 dB) and high bandwidth while amplifying
input signals that are 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 amplifier extends to almost
triple the supply voltage (for G = ½), making the amplifer 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 amp.
The AD8278 and AD8279 can be used as difference amplifiers with
G = ½ or G = 2. They can also be connected in a high precision,
single-ended configuration for non inverting and inverting gains of
−½, −2, +3, +2, +1½, +1, or +½. The AD8278 and AD8279
provide an integrated precision solution that has a smaller size,
lower cost, and better performance than a discrete alternative.
The AD8278 and AD8279 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, which is ideal for battery-operated and portable
systems. For unity-gain difference amplifiers with similar
performance, refer to the
AD8276
and
AD8277
data sheets.
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.
+INB
5
40kΩ
4
20kΩ
8
–VS
Figure 2. AD8279
Table 1. Difference Amplifiers by Category
Low
Distortion
AD8270
AD8271
AD8273
AD8274
AMP03
1
High Voltage
AD628
AD629
Current Sensing
1
AD8202
(U)
AD8203
(U)
AD8205
(B)
AD8206
(B)
AD8216
(B)
Low Power
AD8276
AD8277
U = unidirectional, B = bidirectional.
The AD8278 is available in the space-saving 8-lead MSOP and
SOIC packages, and the AD8279 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.
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.
AD8278/AD8279
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagrams............................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 7
Thermal Resistance ...................................................................... 7
Maximum Power Dissipation ..................................................... 7
Short-Circuit Current .................................................................. 7
ESD Caution.................................................................................. 7
Pin Configurations and Function Descriptions ........................... 8
Typical Performance Characteristics ..............................................9
Theory of Operation ...................................................................... 16
Circuit Information.................................................................... 16
Driving the AD8278 and AD8279 ........................................... 16
Input Voltage Range................................................................... 16
Power Supplies ............................................................................ 17
Applications Information .............................................................. 18
Configurations............................................................................ 18
Differential Output .................................................................... 19
Instrumentation Amplifier........................................................ 19
Outline Dimensions ....................................................................... 20
Ordering Guide .......................................................................... 21
REVISION HISTORY
1/11—Rev. B to Rev. C
Change to Impedance/Differential Parameter, Table 3 ............... 4
Change to Impedance/Differential Parameter, Table 5 ............... 6
4/10—Rev. A to Rev. B
Changed Supply Current Parameters to AD8278 Supply Current
Parameter and AD8279 Supply Current Parameter, Table 5 ...... 6
Updated Outline Dimensions ....................................................... 20
10/09—Rev. 0 to Rev. A
Added AD8279 and 14-Lead SOIC Model .....................Universal
Changes to Features.......................................................................... 1
Changes to General Description .................................................... 1
Change to Table 2 ............................................................................. 3
Change to Table 3 ..............................................................................4
Change to Table 4 ..............................................................................5
Change to Table 5 ..............................................................................6
Added Figure 6 and Table 9 .............................................................8
Changes to Figure 31 and Figure 32............................................. 13
Changes to Figure 40, Figure 41, and Figure 42 ......................... 14
Added Figure 47; Renumbered Sequentially .............................. 15
Changes to Figure 51 to Figure 57................................................ 18
Added Differential Output Section.............................................. 19
Changes to Figure 59...................................................................... 19
Updated Outline Dimensions....................................................... 21
Changes to Ordering Guide .......................................................... 21
7/09—Revision 0: Initial Version
Rev. C | Page 2 of 24
AD8278/AD8279
SPECIFICATIONS
V
S
= ±5 V to ±15 V, V
REF
= 0 V, T
A
= 25°C, R
L
= 10 kΩ connected to ground, G = ½ difference amplifier configuration, unless
otherwise noted.
Table 2.
G=½
Parameter
INPUT CHARACTERISTICS
System Offset
1
Over Temperature
vs. Power Supply
Average Temperature
Coefficient
Common-Mode Rejection
Ratio (RTI)
Input Voltage Range
2
Impedance
3
Differential
Common Mode
DYNAMIC PERFORMANCE
Bandwidth
Slew Rate
Channel Separation
Settling Time to 0.01%
Settling Time to 0.001%
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
6
AD8278 Supply Current
Over Temperature
AD8279 Supply Current
Over Temperature
Operating Voltage Range
7
TEMPERATURE RANGE
Operating Range
1
2
Conditions
Min
Grade B
Typ
Max
50
100
100
2.5
1
Min
Grade A
Typ
50
Max
250
250
5
5
Unit
μV
μV
μV/V
μV/°C
dB
V
kΩ
kΩ
MHz
V/μs
dB
T
A
= −40°C to +85°C
V
S
= ±5 V to ±18 V
T
A
= −40°C to +85°C
V
S
= ±15 V, V
CM
= ±27 V,
R
S
= 0 Ω
0.3
80
−3 (V
S
+ 0.1)
120
30
1
1.4
130
2
74
−3 (V
S
+ 0.1)
120
30
1
1.4
130
+3 (V
S
− 1.5)
+3 (V
S
− 1.5)
1.1
f = 1 kHz
10 V step on output,
C
L
= 100 pF
1.1
9
10
0.005
0.02
1
7
0.01
9
10
0.05
5
12
μs
μs
%
ppm/°C
ppm
T
A
= −40°C to +85°C
V
OUT
= 20 V p-p
V
S
= ±15 V, R
L
= 10 kΩ
T
A
= −40°C to +85°C
−V
S
+ 0.2
±15
200
+V
S
− 0.2
−V
S
+ 0.2
±15
200
1.4
47
+V
S
− 0.2
V
mA
pF
μV p-p
nV/√Hz
μA
μA
μA
μA
V
°C
f = 0.1 Hz to 10 Hz
f = 1 kHz
1.4
47
50
200
250
350
400
±18
+125
50
200
250
350
400
±18
+125
T
A
= −40°C to +85°C
300
T
A
= −40°C to +85°C
±2
−40
300
±2
−40
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 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 22 through Figure 25 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 26 and Figure 28 for details.
7
Unbalanced dual supplies can be used, such as −V
S
= −0.5 V and +V
S
= +2 V. The positive supply rail must be at least 2 V above the negative supply and reference
voltage.
Rev. C | Page 3 of 24
AD8278/AD8279
V
S
= ±5 V to ±15 V, V
REF
= 0 V, T
A
= 25°C, R
L
= 10 kΩ connected to ground, G = 2 difference amplifier configuration, unless
otherwise noted.
Table 3.
G=2
Parameter
INPUT CHARACTERISTICS
System Offset
1
Over Temperature
vs. Power Supply
Average Temperature
Coefficient
Common-Mode
Rejection Ratio (RTI)
Input Voltage Range
2
Impedance
3
Differential
Common Mode
DYNAMIC PERFORMANCE
Bandwidth
Slew Rate
Channel Separation
Settling Time to 0.01%
Settling Time to 0.001%
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
AD8278 Supply Current
Over Temperature
AD8279 Supply Current
Over Temperature
Operating Voltage Range
7
TEMPERATURE RANGE
Operating Range
1
2
Conditions
Min
Grade B
Typ
Max
100
200
200
5
2
Min
Grade A
Typ
Max
100
500
500
10
5
Unit
μV
μV
μV/V
μV/°C
dB
V
kΩ
kΩ
kHz
V/μs
dB
T
A
= −40°C to +85°C
V
S
= ±5 V to ±18 V
T
A
= −40°C to +85°C
V
S
= ±15 V, V
CM
= ±27 V,
R
S
= 0 Ω
0.6
86
−1.5 (V
S
+ 0.1)
30
30
550
1.4
130
2
80
+1.5 (V
S
− 1.5) −1.5 (V
S
+ 0.1)
30
30
550
1.4
130
+1.5 (V
S
− 1.5)
1.1
f = 1 kHz
10 V step on output,
C
L
= 100 pF
1.1
10
11
0.005
0.02
1
7
0.01
10
11
0.05
5
12
μs
μs
%
ppm/°C
ppm
T
A
= −40°C to +85°C
V
OUT
= 20 V p-p
V
S
= ±15 V, R
L
= 10 kΩ,
T
A
= −40°C to +85°C
−V
S
+ 0.2
±15
350
+V
S
− 0.2
−V
S
+ 0.2
±15
350
2.8
90
+V
S
− 0.2
V
mA
pF
μV p-p
nV/√Hz
μA
μA
μA
μA
V
°C
f = 0.1 Hz to 10 Hz
f = 1 kHz
2.8
90
95
200
250
350
400
±18
+125
95
200
250
350
400
±18
+125
6
T
A
= −40°C to +85°C
300
T
A
= −40°C to +85°C
±2
−40
300
±2
−40
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 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 22 through Figure 25 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 26 and Figure 28 for details.
7
Unbalanced dual supplies can be used, such as −V
S
= −0.5 V and +V
S
= +2 V. The positive supply rail must be at least 2 V above the negative supply and reference
voltage.
Rev. C | Page 4 of 24
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