Low Power, Wide Supply Range,
Low Cost Difference Amplifier, G = ½, 2
AD8278
Rev. 0
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Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved.
FEATURES
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
APPLICATIONS
Voltage measurement and monitoring
Current measurement and monitoring
Instrumentation amplifier building block
Portable, battery-powered equipment
Test and measurement
FUNCTIONAL BLOCK DIAGRAM
25
3 1
6
7
4
40kΩ20kΩ
40kΩ
–VS
+VS
–IN
+IN
SENSE
OUT
REF
20kΩ
AD8278
08308-001
Figure 1.
Table 1. Difference Amplifiers by Category
Low
Distortion
High
Voltage
Current
Sensing1
Low Power
AD8270 AD628 AD8202 (U) AD8276
AD8271 AD629 AD8203 (U) AD8277
AD8273 AD8205 (B)
AD8274 AD8206 (B)
AMP03 AD8216 (B)
1 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 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 can be used as a difference amplifier with G = ½
or G = 2. It 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 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 A, 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.
AD8278
Rev. 0 | Page 2 of 24
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 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 ................................................................... 16
Input Voltage Range ................................................................... 16
Power Supplies ............................................................................ 17
Applications Information .............................................................. 18
Configurations ............................................................................ 18
Instrumentation Amplifier........................................................ 19
Outline Dimensions ....................................................................... 20
Ordering Guide .......................................................................... 21
REVISION HISTORY
7/09—Revision 0: Initial Version
AD8278
Rev. 0 | Page 3 of 24
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.
Parameter Conditions
G = ½
Unit
Grade B Grade A
Min Typ Max Min Typ Max
INPUT CHARACTERISTICS
System Offset1 50 100 50 250 µV
vs. Temperature TA = −40°C to +85°C 100 250 µV
Average Temperature
Coefficient TA = −40°C to +85°C 0.3 1 2 5 µV/°C
vs. Power Supply VS = ±5 V to ±18 V 2.5 5 µV/V
Common-Mode Rejection
Ratio (RTI)
VS = ±15 V, VCM = ±27 V,
RS = 0 Ω 80 74 dB
Input Voltage Range2 −3(VS + 0.1) +3(VS − 1.5) −3(VS + 0.1) +3(VS − 1.5) V
Impedance3
Differential 120 120 kΩ
Common Mode 30 30 kΩ
DYNAMIC PERFORMANCE
Bandwidth 1 1 MHz
Slew Rate 1.1 1.4 1.1 1.4 V/µs
Settling Time to 0.01% 10 V step on output,
CL = 100 pF
9 9 µs
Settling Time to 0.001% 10 10 µs
GAIN
Gain Error 0.005 0.02 0.01 0.05 %
Gain Drift TA = −40°C to +85°C 1 5 ppm/°C
Gain Nonlinearity VOUT = 20 V p-p 5 10 ppm
OUTPUT CHARACTERISTICS
Output Voltage Swing4 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 ±15 ±15 mA
Capacitive Load Drive 200 200 pF
NOISE5
Output Voltage Noise f = 0.1 Hz to 10 Hz 1.4 1.4 V p-p
f = 1 kHz 47 50 47 50 nV/√Hz
POWER SUPPLY
Supply Current6 200 200 A
vs. Temperature TA = −40°C to +85°C 250 250 A
Operating Voltage Range7 ±2 ±18 ±2 ±18 V
TEMPERATURE RANGE
Operating Range −40 +125 −40 +125 °C
1 Includes input bias and offset current errors, RTO (referred to output)
2 The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the Input Voltage Range section in the Theory of
Operation 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.
AD8278
Rev. 0 | Page 4 of 24
VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 k connected to ground, G = 2 difference amplifier configuration, unless
otherwise noted.
Table 3.
Parameter Conditions
G = 2
Unit
Grade B Grade A
Min Typ Max Min Typ Max
INPUT CHARACTERISTICS
System Offset1
100 200 100 500 µV
vs. Temperature TA = −40°C to +85°C 200 500 µV
Average Temperature
Coefficient TA = −40°C to +85°C 0.6 2 2 5 µV/°C
vs. Power Supply VS = ±5 V to ±18 V 5 10 µV/V
Common-Mode
Rejection Ratio (RTI)
VS = ±15 V, VCM = ±27 V,
RS = 0 Ω 86 80 dB
Input Voltage Range2 −1.5(VS + 0.1) +1.5(VS − 1.5) −1.5(VS + 0.1) +1.5(VS − 1.5) V
Impedance3
Differential 120 120 kΩ
Common Mode 30 30 kΩ
DYNAMIC PERFORMANCE
Bandwidth 550 550 kHz
Slew Rate 1.1 1.4 1.1 1.4 V/µs
Settling Time to 0.01% 10 V step on output,
CL = 100 pF
10 10 µs
Settling Time to 0.001% 11 11 µs
GAIN
Gain Error 0.005 0.02 0.01 0.05 %
Gain Drift TA = −40°C to +85°C 1 5 ppm/°
C
Gain Nonlinearity VOUT = 20 V p-p 5 10 ppm
OUTPUT CHARACTERISTICS
Output Voltage Swing4
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
±15 ±15 mA
Capacitive Load Drive 350 350 pF
NOISE5
Output Voltage Noise f = 0.1 Hz to 10 Hz 2.8 2.8 V p-p
f = 1 kHz 90 95 90 95 nV/√Hz
POWER SUPPLY
Supply Current6
200 200 A
vs. Temperature TA = −40°C to +85°C 250 250 A
Operating Voltage
Range7
±2 ±18 ±2 ±18 V
TEMPERATURE RANGE
Operating Range −40 +125 −40 +125 °C
1 Includes input bias and offset current errors, RTO (referred to output).
2 The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the section in the The
for details.
Input Voltage Range ory of
Operation
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 Figur through for details. e 20 Figure 23
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 and for details. 24 Figure 26
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.
AD8278
Rev. 0 | Page 5 of 24
VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 k connected to midsupply, G = ½ difference amplifier configuration, unless
otherwise noted.
Table 4.
Parameter Conditions
G = ½
Unit
Grade B Grade A
Min Typ Max Min Typ Max
INPUT CHARACTERISTICS
System Offset1
75 150 75 250 µV
vs. Temperature TA = −40°C to +85°C 150 250 µV
Average Temperature
Coefficient TA = −40°C to +85°C 0.3 1 2 5 µV/°C
vs. Power Supply VS = ±5 V to ±18 V 2.5 5 µV/V
Common-Mode Rejection
Ratio (RTI)
VS = 2.7 V, VCM = 0 V
to 2.4 V, RS = 0 Ω 80 74 dB
VS = ±5 V, VCM = −10 V
to +7 V, RS = 0 Ω 80 74 dB
Input Voltage Range2 −3(VS + 0.1) +3(VS − 1.5) −3(VS + 0.1) +3(VS − 1.5) V
Impedance3
Differential 120 120 kΩ
Common Mode 30 30 kΩ
DYNAMIC PERFORMANCE
Bandwidth 870 870 kHz
Slew Rate 1.3 1.3 V/µs
Settling Time to 0.01% 2 V step on output,
CL = 100 pF, VS = 2.7 V
7 7 µs
GAIN
Gain Error 0.005 0.02 0.01 0.05 %
Gain Drift TA = −40°C to +85°C 1 5 ppm/°C
OUTPUT CHARACTERISTICS
Output Swing4
RL = 10 kΩ ,
TA = −40°C to +85°C −VS + 0.1 +VS − 0.15 −VS + 0.1 +VS − 0.15 V
Short-Circuit Current Limit ±10 ±10 mA
Capacitive Load Drive 200 200 pF
NOISE5
Output Voltage Noise f = 0.1 Hz to 10 Hz 1.4 1.4 V p-p
f = 1 kHz 47 50 47 50 nV/√Hz
POWER SUPPLY
Supply Current6
TA = −40°C to +85°C 200 200 A
Operating Voltage Range 2.0 36 2.0 36 V
TEMPERATURE RANGE
Operating Range −40 +125 −40 +125 °C
1 Includes input bias and offset current errors, RTO (referred to output).
2 The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the section in the
section for details.
Input Voltage Range Theory of Operation
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 Figur through for details. e 20 Figure 23
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 and for details. 25 Figure 26
AD8278
Rev. 0 | Page 6 of 24
VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 k connected to midsupply, G = 2 difference amplifier configuration, unless
otherwise noted.
Table 5.
Parameter Conditions
G = 2
Unit
Grade B Grade A
Min Typ Max Min Typ Max
INPUT CHARACTERISTICS
System Offset1
150 300 150 500 µV
vs. Temperature TA = −40°C to +85°C 300 500 µV
Average Temperature
Coefficient TA = −40°C to +85°C 0.6 2 3 5 µV/°C
vs. Power Supply VS = ±5 V to ±18 V 5 10 µV/V
Common-Mode Rejection
Ratio (RTI)
VS = 2.7 V, VCM = 0 V
to 2.4 V, RS = 0 Ω 86 80 dB
VS = ±5 V, VCM = −10 V
to +7 V, RS = 0 Ω 86 80 dB
Input Voltage Range2 −1.5(VS + 0.1) +1.5(VS − 1.5) −1.5(VS + 0.1) +1.5(VS − 1.5) V
Impedance3
Differential 120 120 kΩ
Common Mode 30 30 kΩ
DYNAMIC PERFORMANCE
Bandwidth 450 450 kHz
Slew Rate 1.3 1.3 V/µs
Settling Time to 0.01% 2 V step on output,
CL = 100 pF, VS = 2.7 V
9 9 µs
GAIN
Gain Error 0.005 0.02 0.01 0.05 %
Gain Drift TA = −40°C to +85°C 1 5 ppm/°C
OUTPUT CHARACTERISTICS
Output Swing4
RL = 10 kΩ,
TA = −40°C to +85°C −VS + 0.1 +VS − 0.15 −VS + 0.1 +VS − 0.15 V
Short-Circuit Current Limit ±10 ±10 mA
Capacitive Load Drive 200 200 pF
NOISE5
Output Voltage Noise f = 0.1 Hz to 10 Hz 2.8 2.8 V p-p
f = 1 kHz 94 100 94 100 nV/√Hz
POWER SUPPLY
Supply Current6
TA = −40°C to +85°C 200 220 A
Operating Voltage Range 2.0 36 2.0 36 V
TEMPERATURE RANGE
Operating Range −40 +125 −40 +125 °C
1 Includes input bias and offset current errors, RTO (referred to output).
2 The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the section in the
section for details.
Input Voltage Range Theory of Operation
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 Figur through for details. e 20 Figure 23
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 and for details. 25 Figure 26
AD8278
Rev. 0 | Page 7 of 24
ABSOLUTE MAXIMUM RATINGS
Table 6.
Parameter Rating
Supply Voltage ±18 V
Maximum Voltage at Any Input Pin −VS + 40 V
Minimum Voltage at Any Input Pin +VS − 40 V
Storage Temperature Range −65°C to +150°C
Specified Temperature Range −40°C to +85°C
Package Glass Transition Temperature (TG) 150°C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
THERMAL RESISTANCE
The θJA values in Table 7 assume a 4-layer JEDEC standard
board with zero airflow.
Table 7. Thermal Resistance
Package Type θJA Unit
8-Lead MSOP 135 °C/W
8-Lead SOIC 121 °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.
2.0
1.6
1.2
0.8
0.4
0
–50 0–25 255075100125
MAXIMUM POWER DISSIPATION (W)
AMBIENT TEMERATURE (°C)
T
J
MAX = 150°C
MSOP
θ
JA
= 135°C/W
SOIC
θ
JA
= 121°C/W
08308-002
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.
ESD CAUTION
AD8278
Rev. 0 | Page 8 of 24
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
REF
1
–IN
2
+IN
3
–VS
4
NC
8
+VS
7
OUT
6
SENSE
5
NC = NO CONNECT
AD8278
TOP VIEW
(Not to Scale)
0
8308-003
Figure 3. MSOP Pin Configuration
REF
1
–IN
2
+IN
3
–VS
4
NC
8
+VS
7
OUT
6
SENSE
5
NC = NO CONNECT
AD8278
TOP VIEW
(Not to Scale)
0
8308-004
Figure 4. SOIC Pin Configuration
Table 8. Pin Function Descriptions
Pin No. Mnemonic Description
1 REF Reference Voltage Input.
2 −IN Inverting Input.
3 +IN Noninverting Input.
4 −VS Negative Supply.
5 SENSE Sense Terminal.
6 OUT Output.
7 +VS Positive Supply.
8 NC No Connect.
AD8278
Rev. 0 | Page 9 of 24
TYPICAL PERFORMANCE CHARACTERISTICS
VS = ±15 V, TA = 25°C, RL = 10 kΩ connected to ground, G = ½ difference amplifier configuration, unless otherwise noted.
600
500
400
300
200
100
0
–150 –100 –50 0 50 100 150
NUMBER OF HITS
SYSTEM OFFSET VOLTAGE (µV)
08308-005
N = 3840
MEAN = –16.8
SD = 41.7673
Figure 5. Distribution of Typical System Offset Voltage, G = 2
800
600
700
500
400
300
200
100
0
–60 –40 –20 0 20 40 60
NUMBER OF HITS
CMRR (µV/V)
08308-006
N = 3837
MEAN = 7.78
SD = 13.569
Figure 6. Distribution of Typical Common-Mode Rejection, G = 2
10
–20
–15
–10
–5
0
5
–50–35–20–5102540557085
CMRR (µV/V)
TEMPERATURE (°C)
08308-007
REPRESENTATIVE DATA
Figure 7. CMRR vs. Temperature, Normalized at 25°C, G = ½
80
–100
–80
–60
–40
–20
0
20
40
60
–50 –35 –20 –5 10 25 40 55 70 85
SYSTEM OFFSET (µV)
TEMPERATURE (°C)
REPRESENTATIVE DATA
08308-008
Figure 8. System Offset vs. Temperature, Normalized at 25°, G = ½
20
–30
–25
–20
–15
–10
–5
0
5
10
15
–50 –35 –20 –5 10 25 40 55 70 85
GAIN ERROR (µV/V)
TEMPERATURE (°C)
REPRESENTATIVE DATA
08308-009
Figure 9. Gain Error vs. Temperature, Normalized at 25°C, G = ½
30
–30
–20
–10
0
10
20
–20 –15 –10 –5 0 5 10 15 20
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= ±15V
V
S
= ±5V
08308-010
Figure 10. Input Common-Mode Voltage vs. Output Voltage,
±15 V and ±5 V Supplies, G = ½
AD8278
Rev. 0 | Page 10 of 24
10
–10
–8
–6
–4
–2
0
2
4
6
8
–0.5 0.5 1.5 2.5 3.5 4.5 5.5
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= 5V
V
REF
= MIDSUPPLY
V
S
= 2.7V
08308-011
Figure 11. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = Midsupply, G = ½
12
–6
–4
–2
0
2
4
6
8
10
–0.5 0.5 1.5 2.5 3.5 4.5 5.5
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= 5V
V
S
= 2.7V
08308-012
V
REF
= 0V
Figure 12. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = 0 V, G = ½
30
–30
–20
–10
0
10
20
–20 –15 –10 –5 0 10 20515
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= ±5V
V
S
= ±15V
08308-013
Figure 13. Input Common-Mode Voltage vs. Output Voltage,
±15 V and ±5 V Supplies, G = 2
5
–3
–2
–1
0
1
2
3
4
–0.5 0.5 1.5 2.5 3.5 4.5 5.5
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= 5V
V
S
= 2.7V
08308-014
V
REF
= MIDSUPPLY
Figure 14. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = Midsupply, G = 2
6
5
–2
–1
0
1
2
3
4
–0.5 0.5 1.5 2.5 3.5 4.5 5.5
COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
S
= 5V
V
S
= 2.7V
08308-015
V
REF
= 0V
Figure 15. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = 0 V, G = 2
18
–36
–30
–24
–18
–12
–6
0
6
12
100 10M1M100k10k1k
GAIN (dB)
FREQUENCY (Hz)
GAIN = 2
GAIN = ½
08308-016
Figure 16. Gain vs. Frequency, ±15 V Supplies
AD8278
Rev. 0 | Page 11 of 24
18
–36
–30
–24
–18
–12
–6
0
6
12
100 10M1M100k10k1k
GAIN (dB)
FREQUENCY (Hz)
GAIN = 2
GAIN = ½
08308-017
Figure 17. Gain vs. Frequency, +2.7 V Single Supply
120
100
80
60
40
20
0
11M100k10k1k10010
CMRR (dB)
FREQUENCY (Hz)
GAIN = 2
GAIN = ½
08308-018
Figure 18. CMRR vs. Frequency
120
100
80
60
40
20
0
11M100k10k1k10010
PSRR (dB)
FREQUENCY (Hz)
–PSRR
+PSRR
08308-019
Figure 19. PSRR vs. Frequency
+
V
S
–0.1
–0.2
–0.3
–0.4
–VS
+0.1
+0.2
+0.3
+0.4
2116141210864
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
SUPPLY VOLTAGE (±VS)
8
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
08308-020
Figure 20. Output Voltage Swing vs. Supply Voltage and Temperature,
RL = 10 kΩ
+
V
S
–0.2
–0.4
–0.6
–0.8
–1.0
–1.2
–VS
+0.2
+0.4
+0.6
+0.8
+1.0
+1.2
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
SUPPLY VOLTAGE (±VS)
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
2116141210864
08308-021
8
Figure 21. Output Voltage Swing vs. Supply Voltage and Temperature,
RL = 2 kΩ
+
V
S
–4
–8
–VS
+4
+8
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
LOAD RESISTANCE (Ω)
1k 100k10k
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
08308-022
Figure 22. Output Voltage Swing vs. RL and Temperature, VS = ±15 V
AD8278
Rev. 0 | Page 12 of 24
+
V
S
–0.5
–1.0
–1.5
–2.0
–V
S
+0.5
+1.0
+1.5
+2.0
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
OUTPUT CURRENT (mA)
01987654321 0
T
A
= –40°C
T
A
= +25°C
T
A
= +85°C
T
A
= +125°C
08308-023
Figure 23. Output Voltage Swing vs. IOUT and Temperature, VS = ±15 V
180
160
170
150
140
130
120
01161412108642
SUPPLY CURRENT (µA)
SUPPLY VOLTAGE (±V)
8
08308-024
Figure 24. Supply Current vs. Dual-Supply Voltage, VIN = 0 V
180
160
170
150
140
130
120
043530252015105
SUPPLY CURRENT (µA)
SUPPLY VOLTAGE (V)
0
08308-025
Figure 25. Supply Current vs. Single-Supply Voltage, VIN = 0 V, VREF = 0 V
250
150
200
100
50
0
–50 –30 –10 10 30 50 70 90 110 130
SUPPLY CURRENT (µA)
TEMPERATURE (°C)
V
S
= ±15V
V
S
= +2.7V
V
REF
= MIDSUPPLY
08308-026
Figure 26. Supply Current vs. Temperature
30
25
20
15
10
5
0
–5
–10
–15
–20
–50 –30 –10 10 30 50 70 90 110 130
SHORT-CIRCUIT CURRENT (mA)
TEMPERATURE (°C)
I
SHORT+
I
SHORT–
08308-027
Figure 27. Short-Circuit Current vs. Temperature
2.0
1.6
1.8
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–50 –30 –10 10 30 50 70 90 110 130
SLEW RATE (V/µs)
TEMPERATURE (°C)
–SLEW RATE
+SLEW RATE
08308-028
Figure 28. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz
AD8278
Rev. 0 | Page 13 of 24
8
–8
–6
–4
–2
0
2
4
6
–5–4–3–2–1012345
NONLINEARITY (2ppm/DIV)
OUTPUT VOLTAGE (V)
08308-029
Figure 29. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ, G = ½
8
–8
–6
–4
–2
0
2
4
6
–10 –8 –6 –4 –2 0 2 4 6 8 10
NONLINEARITY (2ppm/DIV)
OUTPUT VOLTAGE (V)
08308-030
Figure 30. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ, G = 2
TIME (µs)
5V/DIV
40µs/DIV
0.002%/DIV
6.24µs TO 0.01%
7.92µs TO 0.001%
0
8308-031
Figure 31. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = ±15 V, G = ½
TIME (µs)
1V/DIV
0.002%/DIV
3.64µs TO 0.01%
4.12µs TO 0.001%
4µs/DIV
0
8308-032
Figure 32. Large-Signal Pulse Response and Settling Time, 2 V Step,
VS = 2.7 V, G = ½
TIME (µs)
5V/DIV
0.002%/DIV
7.6µs TO 0.01%
9.68µs TO 0.001%
40µs/DIV
0
8308-033
Figure 33. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = ±15 V, G = 2
TIME (µs)
1V/DIV
0.002%/DIV
4.34µs TO 0.01%
5.12µs TO 0.001%
4µs/DIV
08308-034
Figure 34. Large-Signal Pulse Response and Settling Time, 2 V Step,
VS = 2.7 V
AD8278
Rev. 0 | Page 14 of 24
10µs/DIV
2V/DI
V
08308-035
Figure 35. Large-Signal Step Response, G = ½
10µs/DIV
5V/DI
V
08308-036
Figure 36. Large-Signal Step Response, G = 2
30
25
20
15
10
5
0
100 1M100k10k1k
OUTPUT VOLTAGE (V p-p)
FREQUENCY (Hz)
V
S
= ±15V
V
S
= ±5V
08308-037
Figure 37. Maximum Output Voltage vs. Frequency, VS = ±15 V, ±5 V
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
100 1M100k10k1k
OUTPUT VOLTAGE (V p-p)
FREQUENCY (Hz)
V
S
= ±5V
V
S
= ±2.5V
08308-038
Figure 38. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V
20mV/DI
V
40µs/DIV
NO LOAD
R
L
= 200pF
R
L
= 147pF
R
L
= 247pF
08308-039
Figure 39. Small-Signal Step Response for Various Capacitive Loads, G = ½
20mV/DI
V
40µs/DIV
R
L
= 100pF
R
L
= 200pF
R
L
= 247pF
R
L
= 347pF
08308-040
Figure 40. Small-Signal Step Response for Various Capacitive Loads, G = 2
AD8278
Rev. 0 | Page 15 of 24
50
45
40
35
30
25
20
15
10
5
0
02150 20010050
OVERSHOOT (%)
CAPACITIVE LOAD (pF)
50
±2V
±5V
±15V
±18V
08308-041
Figure 41. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = ½
35
30
25
20
15
10
5
0
0350150 250 30020010050
OVERSHOOT (%)
CAPACITIVE LOAD (pF)
±2V
±5V
±15V
±18V
08308-042
Figure 42. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = 2
1k
100
10
0.1 100k10k1k100101
NOISE (nV/ Hz)
FREQUENCY (Hz)
GAIN = 2
GAIN = ½
08308-043
Figure 43. Voltage Noise Density vs. Frequency
1µV/DI
V
1s/DIV
GAIN = 2
GAIN = ½
08308-044
Figure 44. 0.1 Hz to 10 Hz Voltage Noise
AD8278
Rev. 0 | Page 16 of 24
THEORY OF OPERATION
CIRCUIT INFORMATION
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 confi-
gurations, 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.
25
3 1
6
7
4
40kΩ20kΩ
40kΩ
–VS
+VS
–IN
+IN
SENSE
OUT
REF
20kΩ
AD8278
08308-045
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
⎟
⎠
⎞
⎜
⎝
⎛
−
⎟
⎠
⎞
⎜
⎝
⎛+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
=−+ R3
R4
V
R3
R4
R2R1
R2
VV ININ
OUT 1
This equation demonstrates that the gain accuracy and common-
mode rejection ratio of the 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.
The difference amplifier output voltage equation can be reduced to
()
−+ −= ININ
OUT VV
R3
R4
V
as long as the following ratio of the resistors is tightly matched:
R3
R4
R1
R2 =
The resistors on the 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.
AC Performance
Component sizes and trace lengths are much smaller in an IC
than on a PCB, so the corresponding parasitic elements are also
smaller. This results in better ac performance of the 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.
DRIVING THE AD8278
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 common-
mode 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
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.
08308-046
R4
V
IN+
V
IN–
R3
R1
R2
R2
R1 + R2 (V
IN+
)
R2
R1 + R2 (V
IN+
)
Figure 46. Voltage Division in the Difference Amplifier Configuration
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.
AD8278
Rev. 0 | Page 17 of 24
POWER SUPPLIES
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:
V5.1−+<
+S
REF VV
R2R1
R1
For example, when operating on a +VS= 2 V single supply and
VREF = 0 V, it can be seen from Figure 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.
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.
08308-046
R4
R3
R1
R2
R1
R1 + R2 (V
REF
)
R1
R1 + R2 (V
REF
)
V
REF
Figure 47. Ensure Sufficient Voltage Headroom on the Internal Op Amp
Inputs
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.
AD8278
Rev. 0 | Page 18 of 24
APPLICATIONS INFORMATION
CONFIGURATIONS
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.
40kΩ
2
3
5
1
6
20kΩ
40kΩ20kΩ
–IN
OUT
+IN
VOUT = ½(VIN+ − VIN−)
08308-047
Figure 48. Difference Amplifier, Gain = ½
20kΩ
5
1
2
3
6
40kΩ
20kΩ40kΩ
–IN
OUT
+IN
VOUT = 2(VIN+ − VIN−)
08308-048
Figure 49. Difference Amplifier, Gain = 2
40kΩ
2
3
5
1
V
REF
= MIDSUPPLY
6
20kΩ
40kΩ20kΩ
–IN
OUT
+IN
V
OUT
= ½(V
IN+
− V
IN−
) + V
REF
08308-049
Figure 50. Difference Amplifier, Gain = ½, Referenced to Midsupply
20kΩ
5
1
2
3
V
REF
= MIDSUPPLY
6
40kΩ
20kΩ40kΩ
–IN
OUT
+IN
V
OUT
= 2(V
IN+
− V
IN−
) + V
REF
08308-050
Figure 51. Difference Amplifier, Gain = 2, Referenced to Midsupply
40kΩ
2
3
5
1
6
20kΩ
40kΩ
20kΩ
IN
OUT
V
OUT
= –½V
IN
0
8308-051
Figure 52. Inverting Amplifier, Gain = −½
40kΩ
25
6
20kΩ
IN
OUT
3
1
40kΩ
20kΩ
V
OUT
= 1.5V
IN
08308-052
Figure 53. Noninverting Amplifier, Gain = 1.5
20kΩ2
3
5
1
6
40kΩ
20kΩ40kΩ
OUT
IN
V
OUT
= 2V
IN
0
8308-053
Figure 54. Noninverting Amplifier, Gain = 2
Table 9. Difference and Single-Ended Amplifier Configurations
Amplifier Configuration Signal Gain Pin 1 (REF) Pin 2 (VIN−) Pin 3 (VIN+) Pin 5 (SENSE)
Difference Amplifier +½ GND IN− IN+ OUT
Difference Amplifier +2 IN+ OUT GND IN−
Single-Ended Inverting Amplifier −½ GND IN GND OUT
Single-Ended Inverting Amplifier −2 GND OUT GND IN
Single-Ended Non Inverting Amplifier +3⁄2 IN GND IN OUT
Single-Ended Non Inverting Amplifier +3 IN OUT IN GND
Single-Ended Non Inverting Amplifier +½ GND GND IN OUT
Single-Ended Non Inverting Amplifier +1 IN GND GND OUT
Single-Ended Non Inverting Amplifier +1 GND OUT IN GND
Single-Ended Non Inverting Amplifier +2 IN OUT GND GND
AD8278
Rev. 0 | Page 19 of 24
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.
INCORRECT
V
CORRECT
AD8278
OP1177
+
–
VREF
AD8278
REF
0
8308-054
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 common-
mode 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.
R
G
R
F
R
F
–IN
+IN
A1
A2
AD8278
40kΩ
20kΩ
20kΩ
40kΩ
REF
V
OUT
V
OUT
= (1 + 2R
F
/R
G
) (V
IN+
– V
IN–
) × 2
08308-056
Figure 56. Low Power Precision Instrumentation Amplifier
Table 10. Low Power Op Amps
Op Amp (A1, A2) Features
AD8506 Dual micropower op amp
AD8607 Precision dual micropower op amp
AD8617 Low cost CMOS micropower op amp
AD8667 Dual precision CMOS micropower op amp
It is preferable to use dual op amps for the high impedance inputs,
because they have better matched performance and track each
other over temperature. The AD8278 difference amplifier can-
cels 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.
AD8278
Rev. 0 | Page 20 of 24
OUTLINE DIMENSIONS
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.
COMPLIANT TO JEDEC STANDARDS MS-012-A A
012407-A
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
0.50 (0.0196)
0.25 (0.0099) 45°
8°
0°
1.75 (0.0688)
1.35 (0.0532)
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0040)
4
1
85
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2441)
5.80 (0.2284)
0.51 (0.0201)
0.31 (0.0122)
COPLANARITY
0.10
Figure 57. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body (R-8)
Dimensions shown in millimeters and (inches)
COMPLIANT TO JEDEC STANDARDS MO-187-AA
0.80
0.60
0.40
8°
0°
4
8
1
5
PIN 1
0.65 BSC
SEATING
PLANE
0.38
0.22
1.10 MAX
3.20
3.00
2.80
COPLANARITY
0.10
0.23
0.08
3.20
3.00
2.80
5.15
4.90
4.65
0.15
0.00
0
.95
0
.85
0
.75
Figure 58. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
AD8278
Rev. 0 | Page 21 of 24
ORDERING GUIDE
Model Temperature Range Package Description Package Option Branding
AD8278ARZ1
−40°C to +85°C 8-Lead SOIC_N R-8
AD8278ARZ-R71
−40°C to +85°C 8-Lead SOIC_N, 7" Tape and Reel R-8
AD8278ARZ-RL1
−40°C to +85°C 8-Lead SOIC_N, 13" Tape and Reel R-8
AD8278BRZ1
−40°C to +85°C 8-Lead SOIC_N R-8
AD8278BRZ-R71
−40°C to +85°C 8-Lead SOIC_N, 7" Tape and Reel R-8
AD8278BRZ-RL1
−40°C to +85°C 8-Lead SOIC_N, 13" Tape and Reel R-8
AD8278ARMZ1
−40°C to +85°C 8-Lead MSOP RM-8 Y21
AD8278ARMZ-R71
−40°C to +85°C 8-Lead MSOP, 7" Tape and Reel RM-8 Y21
AD8278ARMZ-RL1
−40°C to +85°C 8-Lead MSOP, 13" Tape and Reel RM-8 Y21
AD8278BRMZ1
−40°C to +85°C 8-Lead MSOP RM-8 Y22
AD8278BRMZ-R71
−40°C to +85°C 8-Lead MSOP, 7" Tape and Reel RM-8 Y22
AD8278BRMZ-RL1
−40°C to +85°C 8-Lead MSOP, 13" Tape and Reel RM-8 Y22
1 Z = RoHS Compliant Part.
AD8278
Rev. 0 | Page 22 of 24
NOTES
AD8278
Rev. 0 | Page 23 of 24
NOTES
AD8278
Rev. 0 | Page 24 of 24
NOTES
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08308-0-7/09(0)
