AD AD8279

Preliminary Technical Data
Low Power, Wide Supply Range,
Low Cost Difference Amplifiers, G = ½, 2
AD8279
FEATURES
FUNCTIONAL BLOCK DIAGRAM
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
APPLICATIONS
Voltage measurement and monitoring
Current measurement and monitoring
Instrumentation amplifier building block
Portable, battery-powered equipment
Test and measurement
GENERAL DESCRIPTION
The AD8279 consists of two general-purpose difference
amplifiers intended for precision signal conditioning in power
critical applications that require both high performance and low
power. The AD8279 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 amplifiers extend to almost
triple the supply voltage (for G = ½), making them 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 AD8279 can be used as difference amplifiers 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 AD8279 provide an integrated
precision solution that has a smaller size, lower cost, and better
performance than a discrete alternative.
Figure 1.
The AD8279 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 per channel, which is ideal for battery-operated and
portable systems.
The AD8279 is available in a 14-lead SOIC package. It is
specified for performance over the industrial temperature range
of −40°C to +85°C and are fully RoHS compliant.
Table 1. Difference Amplifiers by Category
Low
Distortion
AD8270
AD8271
AD8273
AD8274
AMP03
1
High
Voltage
AD628
AD629
Current
Sensing1
AD8202 (U)
AD8203 (U)
AD8205 (B)
AD8206 (B)
AD8216 (B)
Low Power
AD8276
AD8277
AD8278
AD8279
U = unidirectional, B = bidirectional.
Rev. PrA
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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.
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Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2009 Analog Devices, Inc. All rights reserved.
AD8279
Preliminary Technical Data
TABLE OF CONTENTS
Features .............................................................................................. 1 ESD Caution...................................................................................7 Applications ....................................................................................... 1 Pin Configurations and Function Descriptions ............................8 General Description ......................................................................... 1 Typical Performance Characteristics ..............................................9 Functional Block Diagram .............................................................. 1 Theory of Operation ...................................................................... 16 Revision History ............................................................................... 2 Circuit Information.................................................................... 16 Specifications..................................................................................... 3 Driving the AD8279................................................................... 16 Absolute Maximum Ratings............................................................ 7 Input Voltage Range ................................................................... 16 Thermal Resistance ...................................................................... 7 Power Supplies ............................................................................ 17 Maximum Power Dissipation ..................................................... 7 Outline Dimensions ....................................................................... 18 Short-Circuit Current .................................................................. 7 REVISION HISTORY
Rev. PrA | Page 2 of 18
Preliminary Technical Data
AD8279
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%
Channel Separation
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
Min
Grade B
Typ
Max
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
130
0.005
TA = −40°C to +85°C
VOUT = 20 V p-p
VS = ±15 V, RL = 10 kΩ
TA = −40°C to +85°C
1.1
dB
+3(VS − 1.5) V
120
30
kΩ
kΩ
1
1.4
MHz
V/μs
9
10
f = 1 kHz
−VS + 0.2
0.02
1
5
+VS − 0.2
1.4
47
9
10
μs
μs
dB
0.05
5
10
%
ppm/°C
ppm
+VS − 0.2
V
mA
pF
130
0.01
−VS + 0.2
±15
200
f = 0.1 Hz to 10 Hz
f = 1 kHz
Unit
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
±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 19 through Figure 22 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 25 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. PrA | Page 3 of 18
AD8279
Preliminary Technical Data
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 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%
Channel Separation
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
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
130
kΩ
kΩ
550
1.4
kHz
V/μs
0.005
0.02
1
VOUT = 20 V p-p
5
−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
dB
0.05
5
10
%
ppm/°
C
ppm
+VS − 0.2
V
130
TA = −40°C to +85°C
VS = ±15 V, RL = 10 kΩ
TA = −40°C to +85°C
120
30
10
11
f = 1 kHz
±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 19 through Figure 22 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 25 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. PrA | Page 4 of 18
Preliminary Technical Data
AD8279
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 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%
Channel Separation
GAIN
Gain Error
Gain Drift
OUTPUT CHARACTERISTICS
Output Swing4
Short-Circuit Current Limit
Capacitive Load Drive
NOISE5
Output Voltage Noise
POWER SUPPLY
Supply Current6
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
130
7
130
μs
dB
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
f = 1 kHz
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 19 through Figure 22 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 25 for details.
2
Rev. PrA | Page 5 of 18
AD8279
Preliminary Technical Data
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 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%
Channel Separation
GAIN
Gain Error
Gain Drift
OUTPUT CHARACTERISTICS
Output Swing4
Short-Circuit Current Limit
Capacitive Load Drive
NOISE5
Output Voltage Noise
POWER SUPPLY
Supply Current6
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
130
9
130
μs
dB
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
f = 1 kHz
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 19 through Figure 22 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 25 for details.
2
Rev. PrA | Page 6 of 18
Preliminary Technical Data
AD8279
ABSOLUTE MAXIMUM RATINGS
2.0
Table 6.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
THERMAL RESISTANCE
Table 7. Thermal Resistance
θJA
105
14-LEAD SOIC
θJA = 105°C/W
1.2
8-LEAD SOIC
θJA = 121°C/W
0.8
8-LEAD MSOP
θJA = 135°C/W
0.4
0
–50
–25
0
25
50
75
100
125
AMBIENT TEMERATURE (°C)
Figure 2. Maximum Power Dissipation vs. Ambient Temperature
SHORT-CIRCUIT CURRENT
The AD8279 has built-in, short-circuit protection that limits the
output current (see Figure 26 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 26, 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.
Package Type
14-Lead SOIC
1.6
07692-002
Rating
±18 V
−VS + 40 V
+VS − 40 V
−65°C to +150°C
−40°C to +85°C
150°C
MAXIMUM POWER DISSIPATION (W)
TJ MAX = 150°C
Parameter
Supply Voltage
Maximum Voltage at Any Input Pin
Minimum Voltage at Any Input Pin
Storage Temperature Range
Specified Temperature Range
Package Glass Transition Temperature (TG)
Unit
°C/W
MAXIMUM POWER DISSIPATION
The maximum safe power dissipation for the AD8279 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. PrA | Page 7 of 18
AD8279
Preliminary Technical Data
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
NC 1
–INA 2
+INA 3
14 REFA
AD8279
AD8277
13 OUTA
12 SENSEA
TOP VIEW
11 +VS
(Not to Scale)
+INB 5
10 SENSEB
–INB 6
9
OUTB
NC 7
8
REFB
NC = NO CONNECT
07692-053
–VS 4
Figure 3. AD8279 14-Lead SOIC Pin Configuration
Table 8. AD8279 Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Mnemonic
NC
−INA
+INA
−VS
+INB
−INB
NC
REFB
OUTB
SENSEB
+VS
SENSEA
OUTA
REFA
Description
No Connect.
Channel A Inverting Input.
Channel A Noninverting Input.
Negative Supply.
Channel B Noninverting Input.
Channel B Inverting Input.
No Connect.
Channel B Reference Voltage Input.
Channel B Output.
Channel B Sense Terminal.
Positive Supply.
Channel A Sense Terminal.
Channel A Output.
Channel A Reference Voltage Input.
Rev. PrA | Page 8 of 18
Preliminary Technical Data
AD8279
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 4. Distribution of Typical System Offset Voltage, G = 2
800
40
55
70
85
Figure 7. 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 5. Distribution of Typical Common-Mode Rejection, G = 2
40
55
70
85
Figure 8. 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)
08308-007
CMRR (µV/V)
25
TEMPERATURE (°C)
Figure 6. CMRR vs. Temperature, Normalized at 25°C, G = ½
–30
–20
–15
–10
–5
0
5
10
15
20
OUTPUT VOLTAGE (V)
Figure 9. Input Common-Mode Voltage vs. Output Voltage,
±15 V and ±5 V Supplies, G = ½
Rev. PrA | Page 9 of 18
08308-010
–40
08308-006
–60
08308-009
–25
0
AD8279
Preliminary Technical Data
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 13. 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 11. Input Common-Mode Voltage vs. Output Voltage,
5 V and 2.7 V Supplies, VREF = 0 V, G = ½
Figure 14. 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 12. Input Common-Mode Voltage vs. Output Voltage,
±15 V and ±5 V Supplies, G = 2
–36
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 15. Gain vs. Frequency, ±15 V Supplies
Rev. PrA | Page 10 of 18
10M
08308-016
–30
08308-013
COMMON-MODE VOLTAGE (V)
VS = 2.7V
0
–3
–0.5
Figure 10. 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
Preliminary Technical Data
AD8279
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
16
18
SUPPLY VOLTAGE (±VS)
08308-020
10k
08308-017
1k
FREQUENCY (Hz)
Figure 19. Output Voltage Swing vs. Supply Voltage and Temperature,
RL = 10 kΩ
Figure 16. 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 20. Output Voltage Swing vs. Supply Voltage and Temperature,
RL = 2 kΩ
Figure 17. 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)
Figure 18. PSRR vs. Frequency
100k
1M
–4
–8
TA = –40°C
TA = +25°C
TA = +85°C
TA = +125°C
+8
+4
–VS
1k
08308-019
PSRR (dB)
–0.3
10k
100k
LOAD RESISTANCE (Ω)
Figure 21. Output Voltage Swing vs. RL and Temperature, VS = ±15 V
Rev. PrA | Page 11 of 18
08308-022
GAIN (dB)
0
–0.2
AD8279
Preliminary Technical Data
+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
TEMPERATURE (°C)
Figure 22. Output Voltage Swing vs. IOUT and Temperature, VS = ±15 V
08308-026
+0.5
Figure 25. Supply Current per Channel 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 23. Supply Current per Channel vs. Dual-Supply Voltage, VIN = 0 V
50
70
90
110
130
Figure 26. Short-Circuit Current per Channel 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 24. Supply Current per Channel vs. Single-Supply Voltage, VIN = 0 V,
VREF = 0 V
Rev. PrA | Page 12 of 18
0
–50
–30
–10
10
30
50
70
90
110
130
TEMPERATURE (°C)
Figure 27. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz
08308-028
0
08308-025
0.2
120
Preliminary Technical Data
AD8279
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 28. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ, G = ½
08308-032
NONLINEARITY (2ppm/DIV)
6
Figure 31. 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 32. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = ±15 V, G = 2
Figure 29. 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 30. Large-Signal Pulse Response and Settling Time, 10 V Step,
VS = ±15 V, G = ½
08308-034
NONLINEARITY (2ppm/DIV)
6
Figure 33. Large-Signal Pulse Response and Settling Time, 2 V Step,
VS = 2.7 V
Rev. PrA | Page 13 of 18
AD8279
Preliminary Technical Data
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 37. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V
5V/DIV
20mV/DIV
Figure 34. Large-Signal Step Response, G = ½
08308-036
RL = 200pF
RL = 147pF
RL = 247pF
10µs/DIV
40µs/DIV
Figure 35. Large-Signal Step Response, G = 2
08308-039
NO LOAD
Figure 38. 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 36. Maximum Output Voltage vs. Frequency, VS = ±15 V, ±5 V
08308-040
OUTPUT VOLTAGE (V p-p)
25
Figure 39. Small-Signal Step Response for Various Capacitive Loads, G = 2
Rev. PrA | Page 14 of 18
Preliminary Technical Data
AD8279
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 40. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = ½
Figure 42. 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 41. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = 2
Rev. PrA | Page 15 of 18
1s/DIV
Figure 43. 0.1 Hz to 10 Hz Voltage Noise
08308-044
0
08308-042
5
08308-043
0
08308-041
5
AD8279
Preliminary Technical Data
THEORY OF OPERATION
CIRCUIT INFORMATION
Each channel of the AD8279 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 AD8279 provides the designer with several
benefits over a discrete design, including smaller size, lower
cost, and better ac and dc performance.
The resistors on the AD8279 are laser trimmed to match accurately.
As a result, the AD8279 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 AD8279.
For example, the positive and negative input terminals of the
AD8279 op amps 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 AD8279
Care should be taken to drive the AD8279 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 AD8279. Because all configurations present
several kilohms (kΩ) of input resistance, the AD8279 does not
require a high current drive from the source and so is easy to
drive.
INPUT VOLTAGE RANGE
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 45, the output voltage is found to be
VOUT
R2 (V )
R1 + R2 IN+
R4
⎛ R2 ⎞⎛
⎟ 1 + R4 ⎞⎟ − V IN − ⎛⎜ R4 ⎞⎟
= V IN + ⎜
⎜ R1 + R2 ⎟⎜⎝
R3 ⎠
⎝ R3 ⎠
⎝
⎠
VIN–
VIN+
This equation demonstrates that the gain accuracy and commonmode rejection ratio of the AD8279 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
VOUT =
R4
(VIN + − VIN − )
R3
as long as the following ratio of the resistors is tightly matched:
R2 R4
=
R1 R3
R3
R1
R2
R2 (V )
R1 + R2 IN+
08308-046
Figure 44. Functional Block Diagram
The AD8279 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 45 shows an example of how the voltage
division works in a difference amplifier configuration. For the
AD8279 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.
Figure 45. Voltage Division in the Difference Amplifier Configuration
The AD8279 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. PrA | Page 16 of 18
Preliminary Technical Data
AD8279
The AD8279 operates extremely well over a very wide range of
supply voltages. They can operate on a single supply as low as 2
V and as high as 36 V, under appropriate setup conditions.
For best performance, the user must exercise care that the setup
conditions ensure that the internal op amp is biased correctly.
The internal input terminals of the op amp must have sufficient
voltage headroom to operate properly. Proper operation of the
part requires at least 1.5 V between the positive supply rail and
the op amp input terminals. This relationship is expressed in
the following equation:
The AD8279 are 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 46. 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 46 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 AD8279. 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. PrA | Page 17 of 18
AD8279
Preliminary Technical Data
OUTLINE DIMENSIONS
Figure 47. 14-Lead Standard Small Outline Package [SOIC_N]
Narrow Body (R-14)
Dimensions shown in millimeters and (inches)
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
PR08445-0-8/09(PrA)
Rev. PrA | Page 18 of 18