AD AD8278BRZ-R7

Low Power, Wide Supply Range,
Low Cost Difference Amplifier, G = ½, 2
AD8278
FEATURES
APPLICATIONS
Voltage measurement and monitoring
Current measurement and monitoring
Instrumentation amplifier building block
Portable, battery-powered equipment
Test and measurement
FUNCTIONAL BLOCK DIAGRAM
+VS
7
AD8278
–IN 2
+IN 3
40kΩ
20kΩ
40kΩ
20kΩ
5
SENSE
6
OUT
1
REF
4
–VS
08308-001
Wide input range beyond supplies
Rugged input overvoltage protection
Low supply current: 200 μA maximum
Low power dissipation: 0.5 mW at VS = 2.5 V
Bandwidth: 1 MHz (G = ½)
CMRR: 80 dB minimum, dc to 20 kHz (G = ½)
Low offset voltage drift: ±2 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 and MSOP packages
Figure 1.
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.
GENERAL DESCRIPTION
The AD8278 is a general-purpose difference amplifier intended
for precision signal conditioning in power critical applications
that require both high performance and low power. The AD8278
provides exceptional common-mode rejection ratio (80 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 amplifier extends to almost
triple the supply voltage (for G = ½), making it 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 amp.
The AD8278 can be used as a difference amplifier with G = ½
or G = 2. It can also be connected in a high precision, singleended configuration for non-inverting and inverting gains of
−½, −2, +3, +2, +1½, +1, or +½. The AD8278 provides an
integrated precision solution that has a smaller size, lower cost,
and better performance than a discrete alternative.
The AD8278 operates 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 makes it ideal for battery-operated and portable
systems.
The AD8278 is available in the space-saving 8-lead MSOP
and SOIC packages. It is specified for performance over the
industrial temperature range of −40°C to +85°C and is fully
RoHS compliant.
Rev. 0
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.
AD8278
TABLE OF CONTENTS
Features .............................................................................................. 1
Typical Performance Characteristics ..............................................9
Applications ....................................................................................... 1
Theory of Operation ...................................................................... 16
Functional Block Diagram .............................................................. 1
Circuit Information.................................................................... 16
General Description ......................................................................... 1
Driving the AD8278................................................................... 16
Revision History ............................................................................... 2
Input Voltage Range ................................................................... 16
Specifications..................................................................................... 3
Power Supplies ............................................................................ 17
Absolute Maximum Ratings............................................................ 7
Applications Information .............................................................. 18
Thermal Resistance ...................................................................... 7
Configurations ............................................................................ 18
Maximum Power Dissipation ..................................................... 7
Instrumentation Amplifier........................................................ 19
Short-Circuit Current .................................................................. 7
Outline Dimensions ....................................................................... 20
ESD Caution .................................................................................. 7
Ordering Guide .......................................................................... 21
Pin Configurations and Function Descriptions ........................... 8
REVISION HISTORY
7/09—Revision 0: Initial Version
Rev. 0 | Page 2 of 24
AD8278
SPECIFICATIONS
VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 kΩ connected to ground, G = ½ difference amplifier configuration, unless
otherwise noted.
Table 2.
G=½
Parameter
INPUT CHARACTERISTICS
System Offset1
vs. Temperature
Average Temperature
Coefficient
vs. Power Supply
Common-Mode Rejection
Ratio (RTI)
Input Voltage Range2
Impedance3
Differential
Common Mode
DYNAMIC PERFORMANCE
Bandwidth
Slew Rate
Settling Time to 0.01%
Settling Time to 0.001%
GAIN
Gain Error
Gain Drift
Gain Nonlinearity
OUTPUT CHARACTERISTICS
Output Voltage Swing4
Short-Circuit Current Limit
Capacitive Load Drive
NOISE5
Output Voltage Noise
POWER SUPPLY
Supply Current6
vs. Temperature
Operating Voltage Range7
TEMPERATURE RANGE
Operating Range
Conditions
Grade B
Typ
Max
Min
50
250
250
μV
μV
0.3
1
2.5
2
5
5
μV/°C
μV/V
+3(VS − 1.5)
74
−3(VS + 0.1)
120
30
1
1.4
10 V step on output,
CL = 100 pF
1.1
dB
+3(VS − 1.5) V
120
30
kΩ
kΩ
1
1.4
MHz
V/μs
9
10
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
−VS + 0.2
0.02
1
5
+VS − 0.2
0.01
−VS + 0.2
±15
200
f = 0.1 Hz to 10 Hz
f = 1 kHz
Unit
100
100
80
−3(VS + 0.1)
1.1
Grade A
Typ
Max
50
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
1.4
47
9
10
μs
μs
0.05
5
10
%
ppm/°C
ppm
+VS − 0.2
V
mA
pF
±15
200
1.4
47
50
50
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 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 20 through Figure 23 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 24 and Figure 26 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. 0 | Page 3 of 24
AD8278
VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 kΩ connected to ground, G = 2 difference amplifier configuration, unless
otherwise noted.
Table 3.
G=2
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%
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
Grade B
Typ
Max
Min
100
500
500
μV
μV
0.6
2
5
2
5
10
μV/°C
μV/V
+1.5(VS − 1.5)
dB
V
80
+1.5(VS − 1.5) −1.5(VS + 0.1)
120
30
550
1.4
10 V step on output,
CL = 100 pF
1.1
120
30
kΩ
kΩ
550
1.4
kHz
V/μs
10
11
TA = −40°C to +85°C
0.005
0.02
1
VOUT = 20 V p-p
5
VS = ±15 V, RL = 10 kΩ
TA = −40°C to +85°C
−VS + 0.2
+VS − 0.2
0.01
−VS + 0.2
±15
350
f = 0.1 Hz to 10 Hz
f = 1 kHz
2.8
90
10
11
μs
μs
0.05
5
10
%
ppm/°
C
ppm
+VS − 0.2
V
±15
350
2.8
90
95
mA
pF
95
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
Unit
200
200
86
−1.5(VS + 0.1)
1.1
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
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 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 20 through Figure 23 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 24 and Figure 26 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. 0 | Page 4 of 24
AD8278
VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 kΩ connected to midsupply, G = ½ difference amplifier configuration, unless
otherwise noted.
Table 4.
G=½
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%
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
Max
Min
75
250
250
μV
μV
0.3
1
2.5
2
5
5
μV/°C
μV/V
74
80
−3(VS + 0.1)
+3(VS − 1.5)
74
−3(VS + 0.1)
+3(VS − 1.5)
dB
V
120
30
kΩ
kΩ
870
1.3
870
1.3
kHz
V/μs
7
7
μs
0.005
−VS + 0.1
0.02
1
+VS − 0.15
0.01
−VS + 0.1
±10
200
1.4
47
TA = −40°C to +85°C
dB
120
30
TA = −40°C to +85°C
f = 0.1 Hz to 10 Hz
f = 1 kHz
Unit
150
150
80
2 V step on output,
CL = 100 pF, VS = 2.7 V
RL = 10 kΩ ,
TA = −40°C to +85°C
Grade A
Typ
Max
75
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
Min
0.05
5
%
ppm/°C
+VS − 0.15
V
mA
pF
±10
200
1.4
47
50
50
μV p-p
nV/√Hz
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 20 through Figure 23 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 25 and Figure 26 for details.
2
Rev. 0 | Page 5 of 24
AD8278
VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 kΩ connected to midsupply, G = 2 difference amplifier configuration, unless
otherwise noted.
Table 5.
G=2
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%
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
Max
Min
150
500
500
μV
μV
0.6
2
5
3
5
10
μV/°C
μV/V
80
86
−1.5(VS + 0.1)
dB
80
+1.5(VS − 1.5) −1.5(VS + 0.1)
dB
+1.5(VS − 1.5) V
120
30
120
30
kΩ
kΩ
450
1.3
450
1.3
kHz
V/μs
9
9
μs
0.005
TA = −40°C to +85°C
−VS + 0.1
0.02
1
+VS − 0.15
0.01
−VS + 0.1
±10
200
f = 0.1 Hz to 10 Hz
f = 1 kHz
Unit
300
300
86
2 V step on output,
CL = 100 pF, VS = 2.7 V
RL = 10 kΩ,
TA = −40°C to +85°C
Grade A
Typ Max
150
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
Min
2.8
94
TA = −40°C to +85°C
0.05
5
%
ppm/°C
+VS − 0.15
V
mA
pF
±10
200
2.8
94
100
100
μV p-p
nV/√Hz
2.0
200
36
2.0
220
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 20 through Figure 23 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 25 and Figure 26 for details.
2
Rev. 0 | Page 6 of 24
AD8278
ABSOLUTE MAXIMUM RATINGS
2.0
Table 6.
THERMAL RESISTANCE
SOIC
θJA = 121°C/W
1.2
0.8
MSOP
θJA = 135°C/W
0.4
0
–50
–25
0
25
50
75
100
125
AMBIENT TEMERATURE (°C)
Figure 2. Maximum Power Dissipation vs. Ambient Temperature
SHORT-CIRCUIT CURRENT
The AD8278 has built-in, short-circuit protection that limits the
output current (see Figure 27 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 2 and Figure 27, 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 7 assume a 4-layer JEDEC standard
board with zero airflow.
Table 7. Thermal Resistance
θJA
135
121
1.6
08308-002
Rating
±18 V
−VS + 40 V
+VS − 40 V
−65°C to +150°C
−40°C to +85°C
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.
Package Type
8-Lead MSOP
8-Lead SOIC
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
MAXIMUM POWER DISSIPATION
The maximum safe power dissipation for the AD8278 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.
ESD CAUTION
Rev. 0 | Page 7 of 24
AD8278
8
NC
REF 1
AD8278
7
–IN 2
TOP VIEW
(Not to Scale)
+VS
6
OUT
5
SENSE
–IN 2
+IN 3
–VS 4
NC = NO CONNECT
NC
7
+VS
6
OUT
5
SENSE
Figure 4. SOIC Pin Configuration
Table 8. Pin Function Descriptions
Mnemonic
REF
−IN
+IN
−VS
SENSE
OUT
+VS
NC
8
NC = NO CONNECT
Figure 3. MSOP Pin Configuration
Pin No.
1
2
3
4
5
6
7
8
AD8278
TOP VIEW
+IN 3 (Not to Scale)
–VS 4
08308-003
REF 1
08308-004
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
Description
Reference Voltage Input.
Inverting Input.
Noninverting Input.
Negative Supply.
Sense Terminal.
Output.
Positive Supply.
No Connect.
Rev. 0 | Page 8 of 24
AD8278
TYPICAL PERFORMANCE CHARACTERISTICS
VS = ±15 V, TA = 25°C, RL = 10 kΩ connected to ground, G = ½ difference amplifier configuration, unless otherwise noted.
600
80
N = 3840
MEAN = –16.8
SD = 41.7673
60
500
SYSTEM OFFSET (µV)
NUMBER OF HITS
40
400
300
200
20
0
–20
–40
–60
100
–150
–100
–50
0
50
100
REPRESENTATIVE DATA
–100
–50
–35
–20
–5
10
08308-005
0
150
SYSTEM OFFSET VOLTAGE (µV)
Figure 5. Distribution of Typical System Offset Voltage, G = 2
800
40
55
70
85
Figure 8. System Offset vs. Temperature, Normalized at 25°, G = ½
20
N = 3837
MEAN = 7.78
SD = 13.569
700
25
TEMPERATURE (°C)
08308-008
–80
15
10
GAIN ERROR (µV/V)
NUMBER OF HITS
600
500
400
300
5
0
–5
–10
–15
200
–20
100
–20
0
20
40
60
REPRESENTATIVE DATA
–30
–50
–35
–20
–5
10
CMRR (µV/V)
Figure 6. Distribution of Typical Common-Mode Rejection, G = 2
40
55
70
85
Figure 9. Gain Error vs. Temperature, Normalized at 25°C, G = ½
30
5
20
COMMON-MODE VOLTAGE (V)
10
0
–5
–10
–15
VS = ±15V
10
0
VS = ±5V
–10
–20
REPRESENTATIVE DATA
–20
–50
–35
–20
–5
10
25
40
55
70
85
TEMPERATURE (°C)
–30
–20
08308-007
CMRR (µV/V)
25
TEMPERATURE (°C)
–15
–10
–5
0
5
10
15
20
OUTPUT VOLTAGE (V)
Figure 7. CMRR vs. Temperature, Normalized at 25°C, G = ½
Figure 10. Input Common-Mode Voltage vs. Output Voltage,
±15 V and ±5 V Supplies, G = ½
Rev. 0 | Page 9 of 24
08308-010
–40
08308-006
–60
08308-009
–25
0
AD8278
10
5
VREF = MIDSUPPLY
VS = 5V
VS = 5V
6
4
2
0
VS = 2.7V
–2
–4
–6
2.5
3.5
4.5
5.5
1
12
–1
1.5
2.5
3.5
4.5
5.5
Figure 14. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = Midsupply, G = 2
6
VREF = 0V
VS = 5V
5
COMMON-MODE VOLTAGE (V)
VS = 5V
8
6
4
2
VS = 2.7V
0
0.5
OUTPUT VOLTAGE (V)
VREF = 0V
10
–2
4
3
2
1
VS = 2.7V
0
1.5
2.5
3.5
4.5
5.5
OUTPUT VOLTAGE (V)
–2
–0.5
08308-012
0.5
0.5
1.5
2.5
3.5
4.5
5.5
OUTPUT VOLTAGE (V)
Figure 12. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = 0 V, G = ½
Figure 15. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = 0 V, G = 2
30
18
VS = ±15V
08308-015
–1
–4
12
20
6
GAIN = 2
0
0
GAIN (dB)
10
VS = ±5V
–10
–6
GAIN = ½
–12
–18
–24
–20
–30
–20
–15
–10
–5
0
5
10
15
20
OUTPUT VOLTAGE (V)
Figure 13. Input Common-Mode Voltage vs. Output Voltage,
±15 V and ±5 V Supplies, G = 2
–36
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 16. Gain vs. Frequency, ±15 V Supplies
Rev. 0 | Page 10 of 24
10M
08308-016
–30
08308-013
COMMON-MODE VOLTAGE (V)
VS = 2.7V
0
–3
–0.5
Figure 11. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = Midsupply, G = ½
COMMON-MODE VOLTAGE (V)
2
08308-014
1.5
08308-011
0.5
OUTPUT VOLTAGE (V)
–6
–0.5
3
–2
–8
–10
–0.5
VREF = MIDSUPPLY
4
COMMON-MODE VOLTAGE (V)
COMMON-MODE VOLTAGE (V)
8
AD8278
18
+VS
–0.1
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
12
GAIN = 2
6
GAIN = ½
–6
–12
–18
–24
–30
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
+0.4
+0.3
+0.2
100k
1M
10M
–VS
2
4
6
8
10
12
14
18
16
SUPPLY VOLTAGE (±VS)
08308-020
10k
08308-017
1k
FREQUENCY (Hz)
Figure 20. Output Voltage Swing vs. Supply Voltage and Temperature,
RL = 10 kΩ
Figure 17. Gain vs. Frequency, +2.7 V Single Supply
120
+VS
–0.2
100
GAIN = ½
80
60
40
0
1
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
–0.6
–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
+0.4
+0.2
–VS
08308-018
20
–0.4
2
4
6
8
10
12
14
16
18
SUPPLY VOLTAGE (±VS)
08308-021
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
GAIN = 2
CMRR (dB)
–0.4
+0.1
–36
100
Figure 21. Output Voltage Swing vs. Supply Voltage and Temperature,
RL = 2 kΩ
Figure 18. CMRR vs. Frequency
+VS
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
120
100
–PSRR
80
60
+PSRR
40
20
0
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
08308-019
PSRR (dB)
–0.3
Figure 19. PSRR vs. Frequency
–4
–8
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
+8
+4
–VS
1k
10k
100k
LOAD RESISTANCE (Ω)
Figure 22. Output Voltage Swing vs. RL and Temperature, VS = ±15 V
Rev. 0 | Page 11 of 24
08308-022
GAIN (dB)
0
–0.2
AD8278
+VS
250
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)
0
–50
08308-023
–VS
–30
–10
10
30
50
70
90
110
130
110
130
TEMPERATURE (°C)
Figure 23. Output Voltage Swing vs. IOUT and Temperature, VS = ±15 V
08308-026
+0.5
Figure 26. Supply Current vs. Temperature
180
30
25
SHORT-CIRCUIT CURRENT (mA)
SUPPLY CURRENT (µA)
170
160
150
140
130
20
15
ISHORT+
10
5
0
–5
–10
ISHORT–
0
2
4
6
8
10
12
14
16
18
SUPPLY VOLTAGE (±V)
–20
–50
08308-024
120
–30
–10
10
Figure 24. Supply Current vs. Dual-Supply Voltage, VIN = 0 V
50
70
90
Figure 27. Short-Circuit Current vs. Temperature
180
2.0
–SLEW RATE
1.8
170
1.6
160
SLEW RATE (V/µs)
SUPPLY CURRENT (µA)
30
TEMPERATURE (°C)
08308-027
–15
150
140
1.4
+SLEW RATE
1.2
1.0
0.8
0.6
0.4
130
5
10
15
20
25
SUPPLY VOLTAGE (V)
30
35
40
Figure 25. Supply Current vs. Single-Supply Voltage, VIN = 0 V, VREF = 0 V
Rev. 0 | Page 12 of 24
0
–50
–30
–10
10
30
50
70
90
110
130
TEMPERATURE (°C)
Figure 28. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz
08308-028
0
08308-025
0.2
120
AD8278
8
4
1V/DIV
2
3.64µs TO 0.01%
4.12µs TO 0.001%
0
–2
0.002%/DIV
–4
–6
4µs/DIV
–4
–3
–2
–1
0
1
2
3
4
5
OUTPUT VOLTAGE (V)
TIME (µs)
08308-029
–8
–5
Figure 29. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ, G = ½
08308-032
NONLINEARITY (2ppm/DIV)
6
Figure 32. Large-Signal Pulse Response and Settling Time, 2 V Step,
VS = 2.7 V, G = ½
8
4
5V/DIV
2
7.6µs TO 0.01%
9.68µs TO 0.001%
0
–2
0.002%/DIV
–6
40µs/DIV
–8
–6
–4
–2
0
2
4
6
8
10
OUTPUT VOLTAGE (V)
TIME (µs)
08308-030
–8
–10
08308-033
–4
Figure 33. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = ±15 V, G = 2
Figure 30. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ, G = 2
5V/DIV
1V/DIV
6.24µs TO 0.01%
7.92µs TO 0.001%
4.34µs TO 0.01%
5.12µs TO 0.001%
0.002%/DIV
0.002%/DIV
TIME (µs)
4µs/DIV
08308-031
40µs/DIV
TIME (µs)
Figure 31. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = ±15 V, G = ½
Rev. 0 | Page 13 of 24
08308-034
NONLINEARITY (2ppm/DIV)
6
Figure 34. Large-Signal Pulse Response and Settling Time, 2 V Step,
VS = 2.7 V
AD8278
5.0
4.5
VS = ±5V
2V/DIV
OUTPUT VOLTAGE (V p-p)
4.0
3.5
3.0
VS = ±2.5V
2.5
2.0
1.5
1.0
10µs/DIV
0
100
1k
10k
100k
1M
FREQUENCY (Hz)
08308-038
08308-035
0.5
Figure 38. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V
5V/DIV
20mV/DIV
Figure 35. Large-Signal Step Response, G = ½
08308-036
RL = 200pF
RL = 147pF
RL = 247pF
10µs/DIV
40µs/DIV
Figure 36. Large-Signal Step Response, G = 2
08308-039
NO LOAD
Figure 39. Small-Signal Step Response for Various Capacitive Loads, G = ½
30
VS = ±15V
20
20mV/DIV
15
10
VS = ±5V
RL = 100pF
RL = 200pF
5
RL = 247pF
RL = 347pF
1k
10k
FREQUENCY (Hz)
100k
1M
40µs/DIV
08308-037
0
100
Figure 37. Maximum Output Voltage vs. Frequency, VS = ±15 V, ±5 V
08308-040
OUTPUT VOLTAGE (V p-p)
25
Figure 40. Small-Signal Step Response for Various Capacitive Loads, G = 2
Rev. 0 | Page 14 of 24
AD8278
50
1k
45
40
±2V
±5V
NOISE (nV/ Hz)
OVERSHOOT (%)
35
30
25
±15V
20
±18V
15
GAIN = 2
100
GAIN = ½
10
0
50
100
150
200
250
CAPACITIVE LOAD (pF)
10
0.1
1
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 41. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = ½
Figure 43. Voltage Noise Density vs. Frequency
35
GAIN = 2
30
±2V
20
15
1µV/DIV
OVERSHOOT (%)
25
±5V
GAIN = ½
±15V
10
±18V
0
50
100
150
200
250
CAPACITIVE LOAD (pF)
300
350
Figure 42. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = 2
Rev. 0 | Page 15 of 24
1s/DIV
Figure 44. 0.1 Hz to 10 Hz Voltage Noise
08308-044
0
08308-042
5
08308-043
0
08308-041
5
AD8278
THEORY OF OPERATION
CIRCUIT INFORMATION
AC Performance
The AD8278 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 AD8278 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 AD8278.
For example, the positive and negative input terminals of the
AD8278 op amp are intentionally not pinned out. By not
connecting these nodes to the traces on the PCB, their capacitance
remains low and balanced, resulting in improved loop stability
and excellent common-mode rejection over frequency.
+VS
DRIVING THE AD8278
7
AD8278
20kΩ
20kΩ
40kΩ
5
SENSE
6
OUT
1
REF
4
–VS
Care should be taken to drive the AD8278 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 commonmode rejection of the AD8278. Because all configurations present
several kilohms (kΩ) of input resistance, the AD8278 does not
require a high current drive from the source and so is easy to
drive.
INPUT VOLTAGE RANGE
Figure 45. 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 46, the output voltage is found to be
⎛ R2 ⎞⎛
⎟ 1 + R4 ⎞⎟ − V IN − ⎛⎜ R4 ⎞⎟
VOUT = V IN + ⎜
⎜ R1 + R2 ⎟⎜⎝
R3 ⎠
⎝ R3 ⎠
⎝
⎠
The AD8278 is 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 46 shows an example of how the voltage
division works in a difference amplifier configuration. For the
AD8278 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+
This equation demonstrates that the gain accuracy and commonmode rejection ratio of the AD8278 is determined primarily by
the matching of resistor ratios. Even a 0.1% mismatch in one
resistor degrades the CMRR to 69 dB for a G = 2 difference
amplifier.
R4
VIN–
VIN+
R3
R1
R2
The difference amplifier output voltage equation can be reduced to
VOUT
R2 (V )
R1 + R2 IN+
R4
(VIN + − VIN − )
=
R3
08308-046
+IN 3
40kΩ
08308-045
–IN
2
Figure 46. Voltage Division in the Difference Amplifier Configuration
as long as the following ratio of the resistors is tightly matched:
R2 R4
=
R1 R3
The resistors on the AD8278 are laser trimmed to match accurately.
As a result, the AD8278 provides superior performance over a
discrete solution, enabling better CMRR, gain accuracy, and
gain drift, even over a wide temperature range.
The AD8278 has 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. 0 | Page 16 of 24
AD8278
The AD8278 operates extremely well over a very wide range of
supply voltages. It 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 AD8278 is typically specified at single- and dual-supplies,
but it 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
VREF
R1 (V
)
R1 + R2 REF
R1
V REF < + VS − 1.5 V
R1 + R2
08308-046
POWER SUPPLIES
Figure 47. Ensure Sufficient Voltage Headroom on the Internal Op Amp
Inputs
For example, when operating on a +VS= 2 V single supply and
VREF = 0 V, it can be seen from Figure 47 that the op amps input
terminals 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 0.66 V (G = ½). Now
the op amp does not have the required 1.5 V headroom and can
not function. Therefore, the user needs to increase the supply
voltage or decrease VREF to restore proper operation.
Use a stable dc voltage to power the AD8278. 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. 0 | Page 17 of 24
AD8278
APPLICATIONS INFORMATION
–IN
The AD8278 can be configured in several ways, as a difference
amplifier or a single-ended amplifier (see Figure 48 to Figure 54).
All of these configurations have excellent gain accuracy and
gain drift because they rely on the internal matched resistors.
Note that Figure 50 shows the AD8278 as a difference amplifier
with a midsupply reference voltage at the noninverting input.
This allows the AD8278 to be used as a level shifter, which is
appropriate in single-supply applications that are referenced
to midsupply. Table 9 lists several single-ended amplifier
configurations that are not illustrated.
5 20kΩ
+IN
1 20kΩ
20kΩ
IN
2 40kΩ
40kΩ
5
OUT
6
20kΩ
3 40kΩ
VOUT = –½VIN
Figure 52. Inverting Amplifier, Gain = −½
1
2 40kΩ
5
OUT
1 20kΩ
IN
2
OUT
6
20kΩ
6
Figure 48. Difference Amplifier, Gain = ½
5 20kΩ
20kΩ
OUT
VOUT = ½(VIN+ − VIN−)
–IN
VREF = MIDSUPPLY
Figure 51. Difference Amplifier, Gain = 2, Referenced to Midsupply
08308-047
3 40kΩ
3
VOUT = 2(VIN+ − VIN−) + VREF
5
6
+IN
40kΩ
08308-051
20kΩ
OUT
3 40kΩ
08308-052
2 40kΩ
2
6
1
–IN
40kΩ
08308-050
CONFIGURATIONS
VOUT = 1.5VIN
Figure 53. Noninverting Amplifier, Gain = 1.5
40kΩ
3
5 20kΩ
40kΩ
08308-048
+IN
1 20kΩ
VOUT = 2(VIN+ − VIN−)
2
6
OUT
Figure 49. Difference Amplifier, Gain = 2
2 40kΩ
20kΩ
IN
5
6
OUT
1 20kΩ
40kΩ
3
08308-053
–IN
VOUT = 2VIN
Figure 54. Noninverting Amplifier, Gain = 2
3 40kΩ
20kΩ
VOUT = ½(VIN+ − VIN−) + VREF
1
VREF = MIDSUPPLY
08308-049
+IN
Figure 50. Difference Amplifier, Gain = ½, Referenced to Midsupply
Table 9. Difference and Single-Ended Amplifier Configurations
Amplifier Configuration
Difference Amplifier
Difference Amplifier
Single-Ended Inverting Amplifier
Single-Ended Inverting Amplifier
Single-Ended Non Inverting Amplifier
Single-Ended Non Inverting Amplifier
Single-Ended Non Inverting Amplifier
Single-Ended Non Inverting Amplifier
Single-Ended Non Inverting Amplifier
Single-Ended Non Inverting Amplifier
Signal Gain
+½
+2
−½
−2
+3⁄2
+3
+½
+1
+1
+2
Pin 1 (REF)
GND
IN+
GND
GND
IN
IN
GND
IN
GND
IN
Rev. 0 | Page 18 of 24
Pin 2 (VIN−)
IN−
OUT
IN
OUT
GND
OUT
GND
GND
OUT
OUT
Pin 3 (VIN+)
IN+
GND
GND
GND
IN
IN
IN
GND
IN
GND
Pin 5 (SENSE)
OUT
IN−
OUT
IN
OUT
GND
OUT
OUT
GND
GND
AD8278
–IN
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 55.
40kΩ
RF
20kΩ
RG
RF
40kΩ
+IN
REF
AD8278
VOUT = (1 + 2RF/RG) (VIN+ – VIN–) × 2
Figure 56. Low Power Precision Instrumentation Amplifier
REF
V
AD8278
REF
A2
AD8278
VOUT
20kΩ
CORRECT
08308-056
INCORRECT
A1
V
Table 10. Low Power Op Amps
+
Op Amp (A1, A2)
AD8506
AD8607
AD8617
AD8667
–
08308-054
OP1177
Figure 55. Driving the Reference Pin
INSTRUMENTATION AMPLIFIER
The AD8278 can be used as a building block for a low power,
low cost instrumentation amplifier. An instrumentation amplifier
provides high impedance inputs and delivers high commonmode rejection. Combining the AD8278 with an Analog Devices,
Inc., low power amplifier (see Table 10) creates a precise, power
efficient voltage measurement solution suitable for power
critical systems.
Features
Dual micropower op amp
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 AD8278 difference amplifier cancels 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.
Rev. 0 | Page 19 of 24
AD8278
OUTLINE DIMENSIONS
5.00 (0.1968)
4.80 (0.1890)
5
1
4
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
6.20 (0.2441)
5.80 (0.2284)
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.31 (0.0122)
COPLANARITY
0.10
SEATING
PLANE
0.50 (0.0196)
0.25 (0.0099)
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 57. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body (R-8)
Dimensions shown in millimeters and (inches)
3.20
3.00
2.80
8
3.20
3.00
2.80
1
5
5.15
4.90
4.65
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
45°
0.23
0.08
8°
0°
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 58. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
Rev. 0 | Page 20 of 24
0.80
0.60
0.40
012407-A
8
4.00 (0.1574)
3.80 (0.1497)
AD8278
ORDERING GUIDE
Model
AD8278ARZ 1
AD8278ARZ-R71
AD8278ARZ-RL1
AD8278BRZ1
AD8278BRZ-R71
AD8278BRZ-RL1
AD8278ARMZ1
AD8278ARMZ-R71
AD8278ARMZ-RL1
AD8278BRMZ1
AD8278BRMZ-R71
AD8278BRMZ-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
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
Z = RoHS Compliant Part.
Rev. 0 | Page 21 of 24
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
Branding
Y21
Y21
Y21
Y22
Y22
Y22
AD8278
NOTES
Rev. 0 | Page 22 of 24
AD8278
NOTES
Rev. 0 | Page 23 of 24
AD8278
NOTES
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08308-0-7/09(0)
Rev. 0 | Page 24 of 24