ADA4091-2 Micropower, Single-Supply, Rail-to

Micropower, Single-Supply, Rail-to-Rail
Input/Output Operational Amplifier
ADA4091-2
PIN CONFIGURATION
Single-supply operation: 3 V to 36 V
Wide input voltage range
Rail-to-rail output swing
Low supply current: 250 μA/amp
Wide bandwidth: 1.2 MHz
Slew rate: 0.46 V/μs
Low offset voltage: 500 μV maximum
No phase reversal
OUTA 1
8
+V
ADA4091-2
7
OUTB
TOP VIEW
–V 4 (Not to Scale)
6
–INB
5
+INB
–INA 2
+INA 3
07671-001
FEATURES
Figure 1. 8-Lead, Narrow Body SOIC
APPLICATIONS
Industrial process control
Battery-powered instrumentation
Power supply control and protection
Telecommunications
Remote sensors
Low voltage strain gage amplifiers
DAC output amplifiers
GENERAL DESCRIPTION
The ADA4091-2 is a dual, micropower, single-supply, 1.2 MHz
bandwidth amplifier featuring rail-to-rail inputs and outputs.
It is guaranteed to operate from a +3 V single supply as well as
from ±15 V dual supplies.
The ADA4091 family of op amps features a unique input stage
that allows the input voltage to safely exceed either supply
without any phase inversion or latch-up. The output voltage
swings to within 10 mV of the supplies.
Applications for these amplifiers include portable telecommunications equipment, power supply control and protection,
and interface for transducers with wide output ranges. Sensors
requiring a rail-to-rail input amplifier include Hall effect, piezoelectric, and resistive transducers.
The ability to swing rail-to-rail at both the input and output
enables designers to build multistage filters in single-supply
systems and to maintain high signal-to-noise ratios.
The ADA4091 family of op amps is specified over the extended
industrial temperature range of −40°C to +125°C. The ADA4091-2
is part of a growing family of 36 V, low power op amps from
Analog Devices, Inc. (see Table 1).
The ADA4091-2 is available in an 8-lead plastic SOIC surfacemount package.
Table 1. Low Power, 36 V Operational Amplifiers
Family
Single
Dual
Quad
Rail-to-Rail I/O
PJFET
ADA4091-2
AD8682
AD8684
Low Noise
OP1177
OP2177
OP4177
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
©2008 Analog Devices, Inc. All rights reserved.
ADA4091-2
TABLE OF CONTENTS
Features .............................................................................................. 1 Thermal Resistance .......................................................................6 Applications ....................................................................................... 1 ESD Caution...................................................................................6 Pin Configuration ............................................................................. 1 Typical Performance Characteristics ..............................................7 General Description ......................................................................... 1 Theory of Operation ...................................................................... 13 Revision History ............................................................................... 2 Input Overvoltage Protection ................................................... 14 Specifications..................................................................................... 3 Outline Dimensions ....................................................................... 15 Electrical Specifications ............................................................... 3 Ordering Guide .......................................................................... 15 Absolute Maximum Ratings............................................................ 6 REVISION HISTORY
10/08—Revision 0: Initial Version
Rev. 0 | Page 2 of 16
ADA4091-2
SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
VSY = ±1.5 V, VCM = 0.15 V, VO = 1.4 V, TA = 25°C, unless otherwise noted.
Table 2.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Symbol
Conditions
VOS
−40°C ≤ TA ≤ +125°C
Input Bias Current
IB
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large Signal Voltage Gain
AVO
Offset Voltage Drift
OUTPUT CHARACTERISTICS
Output Voltage High
Output Voltage Low
Short-Circuit Limit
Open-Loop Impedance
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current per Amplifier
DYNAMIC PERFORMANCE
Slew Rate
Settling Time
Gain Bandwidth Product
Phase Margin
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
±1.5 V < VSY ± 18 V
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ, VO = 0.3 V to 2.7 V
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ, VO = 0.3 V to 2.7 V
−40°C ≤ TA ≤ +125°C
Min
Typ
Max
Unit
−500
−1.0
−50
−55
−275
−5
−5
−75
−1.5
76
70
106
100
93
85
+45
+500
+1.0
+50
+55
+275
+5
+5
+75
+1.5
2.5
μV
mV
nA
nA
nA
nA
nA
nA
V
dB
dB
dB
dB
dB
dB
μV/°C
±31
102
V
V
V
V
V
V
V
V
mA
Ω
∆VOS/∆T
VOH
VOL
ISC
ZOUT
PSRR
ISY
RL = 100 kΩ to GND
−40°C to +125°C
RL = 10 kΩ to GND
−40°C to +125°C
RL = 100 kΩ to GND
−40°C to +125°C
RL = 10 kΩ to GND
−40°C to +125°C
Sink/source = −40°C to +125°C
f = 1 MHz, AV = 1
1.495
1.490
1.475
1.455
VSY = 2.7 V to 36 V
−40°C ≤ TA ≤ +125°C
IO = 0 mA
−40°C ≤ TA ≤ +125°C
100
100
−1.498
−1.498
−1.495
−1.491
200
300
dB
dB
μA
μA
SR
tS
GBP
ΦM
RL = 100 kΩ, CL = 30 pF
To 0.01%
0.46
22
1.22
69
V/μs
μs
MHz
Degrees
en p-p
en
0.1 Hz to 10 Hz
f = 1 kHz
2
24
μV p-p
nV/√Hz
Rev. 0 | Page 3 of 16
ADA4091-2
VO = ±5.0 V, −4.9 V ≤ VCM ≤ +4.9 V, TA = 25°C, unless otherwise noted.
Table 3.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Input Bias Current
Symbol
Conditions
Min
Typ
Max
Unit
−500
−1.0
+141
−40°C ≤ TA ≤ +125°C
+500
+1.00
60
150
2
30
+5
μV
mV
nA
nA
nA
nA
V
dB
dB
dB
dB
dB
dB
VOS
IB
30
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
−40°C ≤ TA ≤ +125°C
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large Signal Voltage Gain
AVO
OUTPUT CHARACTERISTICS
Output Voltage High
VOH
Output Voltage Low
Short-Circuit Limit
Open-Loop Impedance
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current per Amplifier
DYNAMIC PERFORMANCE
Slew Rate
Gain Bandwidth Product
Phase Margin
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
VOL
ISC
ZOUT
PSRR
ISY
±1.5 V < VSY ±18 V
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ, VO = ±4.7 V
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ, VO = ±4.7 V
−40°C ≤ TA ≤ +125°C
−5
88
82
113
103
98
87
RL = 100 kΩ to GND
−40°C to +125°C
RL =10 kΩ to GND
–40°C ≤ TA ≤ +125°C
RL = 100 kΩ to GND
−40°C to +125°C
RL =10 kΩ to GND
–40°C ≤ TA ≤ +125°C
Sink/source = −40°C to +125°C
f = 1 MHz, AV = 1
4.980
4.980
4.950
4.900
VSY = 2.7 V to 36 V
−40°C ≤ TA ≤ +125°C
VO = 0 V
−40°C ≤ TA ≤ +125°C
100
100
4.990
4.970
−4.990
−4.980
−4.980
−4.975
±20
77
180
225
300
V
V
V
V
V
V
V
V
mA
Ω
dB
dB
μA
μA
SR
GBP
ΦM
RL = 100 kΩ, CL = 30 pF
0.46
1.22
70
V/μs
MHz
Degrees
en p-p
en
0.1 Hz to 10 Hz
f = 1 kHz
0.8
24
μV p-p
nV/√Hz
Rev. 0 | Page 4 of 16
ADA4091-2
VSY = ±15.0 V, −14.9 V ≤ VCM ≤ +14.9 V, TA = 25°C, unless otherwise noted.
Table 4.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Symbol
Conditions
VOS
−40°C ≤ TA ≤ +125°C
Input Bias Current
IB
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large Signal Voltage Gain
AVO
OUTPUT CHARACTERISTICS
Output Voltage High
VOH
Output Voltage Low
Short-Circuit Limit
Open-Loop Impedance
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current per Amplifier
DYNAMIC PERFORMANCE
Slew Rate
Gain Bandwidth Product
Phase Margin
Channel Separation
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
VOL
ISC
ZOUT
PSRR
ISY
±1.5 V < VSY < ±18 V
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ, VO = ±14.7 V
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ, VO = ±14.7 V
−40°C ≤ TA ≤ +125°C
Min
−500
−1.2
−55
−80
−510
−2
−10
−140
−5
95
90
116
106
102
92
RL = 100 kΩ to GND
−40°C to +125°C
RL = 10 kΩ to GND
–40°C ≤ TA ≤ +125°C
RL = 100 kΩ to GND
−40°C to +125°C
RL = 10 kΩ to GND
−40°C to +125°C
Sink/source = −40°C to 125°C
f = 1 MHz, AV = 1
14.975
14.950
14.900
14.800
VSY = 2.7 V to 36 V
−40°C ≤ TA ≤ +125°C
IO = 0 mA
−40°C ≤ TA ≤ +125°C
100
100
SR
GBP
ΦM
CS
RL = 100 kΩ, CL = 30 pF
en p-p
en
Typ
Max
Unit
+500
+1.20
+55
+80
+510
+2
+10
+140
+5
μV
mV
nA
nA
nA
nA
nA
nA
V
dB
dB
dB
dB
dB
dB
−14.990
−1.4990
−14.950
−14.940
±20
71
250
350
V
V
V
V
V
V
V
V
mA
Ω
dB
dB
μA
μA
f = 1 kHz
0.46
1.27
72
100
V/μs
MHz
Degrees
dB
0.1 Hz to 10 Hz
f = 1 kHz
0.8
25
μV p-p
nV/√Hz
Rev. 0 | Page 5 of 16
ADA4091-2
ABSOLUTE MAXIMUM RATINGS
Table 5.
Parameter
Supply Voltage
Input Voltage
Differential Input Voltage 1
Output Short-Circuit Duration to GND
Storage Temperature Range
Operating Temperature Range
Junction Temperature Range
Lead Temperature (Soldering, 60 sec)
1
Input current should be limited to ±5 mA.
Rating
36 V
Refer to the Input
Overvoltage Protection
section
±VSY
Indefinite
–65°C to +150°C
–40°C to +125°C
–65°C to +150°C
300°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
θJA is specified for the device soldered on a 4-layer JEDEC
standard PCB with zero air flow.
Table 6. Thermal Resistance
Package Type
8-Lead SOIC (R-8)
ESD CAUTION
Rev. 0 | Page 6 of 16
θJA
155
θJC
45
Unit
°C/W
ADA4091-2
TYPICAL PERFORMANCE CHARACTERISTICS
200
10,000
ADA4091-2
TA = 25°C
VSY = ±1.5V
180
160
1000
120
100
80
60
100
VDD – VOH
10
VOL – VSS
1
40
20
50
100
150
200
250
OPEN-LOOP GAIN (dB)
FREQUENCY
150
100
80
80
60
60
4
5
6
7
8
TCVOS (µV/°C)
ADA4091-2
VSY = ±1.5V
RL = 1MΩ
CL = 35pF
300
0
10k
100k
–20
10M
1M
FREQUENCY (Hz)
Figure 6. Open-Loop Gain and Phase vs. Frequency
Figure 3. Input Offset Voltage vs. Temperature
350
40
20
–20
1k
07671-035
3
GAIN
20
0
2
100
40
50
1
100
PHASE
200
0
10
100
ADA4091-2
–40°C ≤ TA ≤ +125°C
VSY = ±1.5V
–1
1
Figure 5. Dropout Voltage vs. Load Current
300
0
0.1
LOAD CURRENT (mA)
Figure 2. Input Offset Voltage Distribution
250
0.01
PHASE (Degrees)
0
VOS (µV)
07671-007
–250 –200 –150 –100 –50
ADA4091-2
VSY = ±1.5V
0.1
0.001
07671-034
0
07671-017
VOUT TO RAIL (mV)
FREQUENCY
140
50
ADA4091-2
VSY = ±1.5V
40
AV = 100
250
100
50
+85°C
0
–50
–100
–150
–1.5
–40°C
–1.0
–0.5
0
0.5
1.0
1.5
VCM (V)
20
AV = 10
10
0
AV = 1
ADA4091-2
–10 V = ±1.5V
SY
RL = 1MΩ
CL = 35pF
–20
10
100
+25°C
07671-033
IB (nA)
150
30
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 4. Input Bias Current vs. Input Common-Mode Voltage
Figure 7. Closed-Loop Gain vs. Frequency
Rev. 0 | Page 7 of 16
10M
07671-010
CLOSED-LOOP GAIN (dB)
+125°C
200
ADA4091-2
3.0
1k
2.5
VOUT SWING (V)
100
10
AV = 10
1.5
1.0
10
100
1k
10k
100k
1M
10M
FREQUENCY (Hz)
ADA4091-2
VSUPP = ±1.5V
VIN = 2.8V p-p
RL = 100kΩ
0
100
225
1.5
200
0
FREQUENCY
ADA4091-2
VSY = ±1.5V
TA = 25°C
RL = 100kΩ
CL = 100pF
AV = +1
–0.5
–1.0
125
100
75
50
–1.5
25
5
10
15
20
25
30
35
40
45
50
TIME (µs)
0
07671-025
0
–250 –200 –150 –100 –50
Figure 9. Large Signal Transient Response
400
0.04
350
100
150
200
250
ADA4091-2
–40°C ≤ TA ≤ +125°C
VSY = ±5V
300
FREQUENCY
0.02
ADA4091-2
VSY = ±1.5V
TA = 25°C
RL = 100kΩ
CL = 100pF
AV = +1
250
200
150
100
–0.06
50
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
TIME (µs)
07671-028
VOUT (V)
50
Figure 12. Input Offset Voltage Distribution
0.06
–0.08
0
VOS (µV)
07671-037
VOUT (V)
ADA4091-2
TA = 25°C
VSY = ±5V
150
0.5
–0.04
1M
175
1.0
–0.02
100k
Figure 11. Output Swing vs. Frequency
2.0
0
10k
FREQUENCY (Hz)
Figure 8. Output Impedance vs. Frequency
–2.0
1k
07671-036
0.5
ADA4091-2
TA = 25°C
VSY = ±1.5V
0
–1
0
1
2
3
4
5
6
7
TCVOS (µV/°C)
Figure 13. Input Offset Voltage vs. Temperature
Figure 10. Small Signal Transient Response
Rev. 0 | Page 8 of 16
8
07671-038
0.1
2.0
AV = 1
1
07671-013
ZOUT (Ω)
AV = 100
ADA4091-2
100
100
6
VOUT (V)
2
0
ADA4091-2
VSY = ±5V
TA = 25°C
RL = 100kΩ
CL = 100pF
AV = +1
–2
5
10
15
20
25
30
35
40
45
50
TIME (µs)
07671-026
0
80
60
60
GAIN
40
40
20
20
0 ADA4091-2
VSY = ±5V
RL = 1MΩ
CL = 35pF
–20
1k
10k
–4
–6
80
0
100k
–20
10M
1M
07671-005
OPEN-LOOP GAIN (dB)
4
PHASE (Degrees)
PHASE
FREQUENCY (Hz)
Figure 17. Open-Loop Gain and Phase vs. Frequency
Figure 14. Large Signal Transient Response
1k
0.06
0.04
100
ADA4091-2
VSY = ±5V
TA = 25°C
RL = 100kΩ
CL = 100pF
AV = +1
0
–0.02
ZOUT (Ω)
AV = 100
10
AV = 10
–0.04
1
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
TIME (µs)
0.1
07671-029
–0.08
10
500
10k
100k
1M
10M
10
ADA4091-2
VSY = ±5V
9
8
300
VOUT SWING (V)
7
200
+125°C
100
+85°C
+25°C
6
5
4
3
0
2
–100
1
–40°C
–4
–3
–2
–1
0
1
2
3
4
VCM (V)
5
ADA4091-2
VSY = ±5V
VIN = 9.8V p-p
RL = 100kΩ
0
100
07671-032
IB (nA)
1k
Figure 18. Output Impedance vs. Frequency
400
–5
100
FREQUENCY (Hz)
Figure 15. Small Signal Transient Response
–200
ADA4091-2
TA = 25°C
VSY = ±5V
AV = 1
07671-012
–0.06
1k
10k
100k
FREQUENCY (Hz)
Figure 19. Output Voltage Swing vs. Frequency
Figure 16. Input Bias Current vs. Common-Mode Voltage
Rev. 0 | Page 9 of 16
1M
07671-015
VOUT (V)
0.02
ADA4091-2
350
10,000
ADA4091-2
TA = –40°C AND +125°C
VSY = ±15V
300
1000
100
FREQUENCY
VOUT TO RAIL (mV)
250
VDD – VOH
VOL – VSS
10
200
150
100
1
0.01
0.1
1
10
100
LOAD CURRENT (mA)
0
07671-018
0.1
0.001
–1
0
1
3
4
5
6
7
8
TCVOS (µV/°C)
Figure 20. Dropout Voltage vs. Load Current
Figure 23. Offset Voltage TC
50
40
2
07671-042
50
ADA4091-2
VSY = ±5V
700
AV = 100
600
ADA4091-2
VSY = ±15V
10
200
–100
1k
10k
100k
1M
10M
–300
–15
–10
–5
0
5
10
Figure 24. Input Bias Current vs. Common-Mode Voltage
Figure 21. Closed-Loop Gain vs. Frequency
250
100
ADA4091-2
TA = 25°C
VSY = ±15V
OPEN-LOOP GAIN (dB)
150
100
50
80
80
60
60
100
150
VOS (µV)
200
250
07671-041
50
Figure 22. Input Offset Voltage Distribution
GAIN
40
40
20
0
0
100
PHASE
200
–250 –200 –150 –100 –50
15
VCM (V)
07671-031
–40°C
–200
FREQUENCY (Hz)
FREQUENCY
+25°C
0
20
ADA4091-2
VSY = ±15V
RL = 1MΩ
CL = 35pF
–20
1k
0
10k
100k
1M
FREQUENCY (Hz)
Figure 25. Open-Loop Gain and Phase vs. Frequency
Rev. 0 | Page 10 of 16
PHASE (Degrees)
ADA4091-2
–10 VSY = ±5V
RL = 1MΩ
CL = 35pF
–20
10
100
0
+85°C
100
AV = 1
–20
10M
07671-006
0
+125°C
300
IB (nA)
20
400
AV = 10
07671-009
CLOSED-LOOP GAIN (dB)
500
30
ADA4091-2
10,000
20
15
1000
VOUT TO RAIL (mV)
10
VOUT (V)
5
ADA4091-2
VSY = ±15V
TA = 25°C
RL = 100kΩ
CL = 100pF
AV = +1
0
–5
–10
VDD – VOH
100
VOL – VSS
10
1
–15
25
50
75
100
125
150
175
200
TIME (µs)
0.01
0.1
1
10
100
LOAD CURRENT (mA)
07671-019
0
ADA4091-2
VSY = ±15V
0.1
0.001
07671-027
–20
–25
Figure 29. Dropout Voltage vs. Load Current
Figure 26.Large Signal Transient Response
1k
0.06
0.04
100
–0.02
–0.04
AV = 100
10
AV = 10
1
–0.06
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
TIME (µs)
0.1
10
07671-030
10k
100k
1M
10M
Figure 30. Output Impedance vs. Frequency
50
35
40
CLOSED-LOOP GAIN (dB)
30
25
20
15
10
ADA4091-2
VSY = ±15V
VIN = 29.8V p-p
RL = 100kΩ
0
100
1k
10k
100k
FREQUENCY (Hz)
1M
07671-016
VOUT SWING (V)
1k
FREQUENCY (Hz)
Figure 27. Small Signal Transient Response
5
100
AV = 100
30
20
AV = 10
10
0
AV = 1
–10
ADA4091-2
–20 VSY = ±15V
RL = 1MΩ
CL = 35pF
–30
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 31. Closed-Loop Gain vs. Frequency
Figure 28. Output Voltage Swing vs. Frequency
Rev. 0 | Page 11 of 16
10M
07671-008
–0.08
ADA4091-2
TA = 25°C
VSY = ±15V
AV = 1
07671-011
ADA4091-2
VSY = ±15V
TA = 25°C
RL = 100kΩ
CL = 100pF
AV = +1
0
ZOUT (Ω)
VOUT (V)
0.02
ADA4091-2
100
0.5
ADA4091-2
VSY = ±1.5V, ±5V, ±15V
0.4
80
0.3
60
0.1
PSRR (dB)
0
–0.1
20
–0.2
–0.3
ADA4091-2
VSY = ±15V
1
2
3
4
5
6
7
8
9
10
TIME (Seconds)
–20
100
07671-043
0
1k
10M
ADA4091-2
450 TA = 25°C
400
–80
350
300
–90
ISY (µA)
CHANNEL SEPARATION (dB)
1M
500
ADA4091-2
VSY = ±15V
–70
–100
250
200
150
–110
100
–120
50
100
10
1k
10k
100k
FREQUENCY (Hz)
07671-044
–130
Figure 33. Channel Separation vs. Frequency
110
90
80
70
VSY = ±1.5V
60
50
40
30
20
1k
10k
100k
FREQUENCY (Hz)
1M
10M
07671-002
10
0
100
0
0
5
10
15
20
25
30
VSY (V)
Figure 36. Supply Current vs. Supply Voltage
ADA4091-2
VSY = ±5V, ±15V
100
CMRR (dB)
100k
Figure 35. PSRR vs. Frequency
Figure 32. Voltage Noise, V p-p
–60
10k
FREQUENCY (Hz)
07671-003
0
–0.4
–0.5
PSRR+
PSRR–
40
Figure 34. CMRR vs. Frequency
Rev. 0 | Page 12 of 16
35
07671-004
NOISE (µV)
0.2
ADA4091-2
THEORY OF OPERATION
A common practice in bipolar amplifiers to protect the input
transistors from large differential voltages is to include series
resistors and differential diodes. (See Figure 39 for the full input
protection circuitry.) These diodes turn on whenever the differential voltage exceeds approximately 0.6 V. In this condition,
current flows between the input pins, limited only by the two
5 kΩ resistors. Evaluate each circuit carefully to make sure that
the increase in current does not affect performance.
The ADA4091-2 is a single-supply, micropower amplifier
featuring rail-to-rail inputs and outputs. To achieve wide input
and output ranges, this amplifier employs unique input and
output stages. In Figure 37, the input stage comprises two
differential pairs, a PNP pair and an NPN pair. These two
stages do not work in parallel. Instead, only one stage is on
for any given input signal level. The PNP stage (Transistor Q1
and Transistor Q2) is required to ensure that the amplifier
remains in the linear region when the input voltage approaches
and reaches the negative rail. Alternatively, the NPN stage
(Transistor Q5 and Transistor Q6) is needed for input voltages
up to and including the positive rail.
The output stage in the ADA4091-2 device uses a PNP and
an NPN transistor, as do most output stages. However, Q32
and Q33, the output transistors, are actually connected with
their collectors to the output pin to achieve the rail-to-rail
output swing.
For the majority of the input common-mode range, the PNP
stage is active, as shown in Figure 4. Notice that the bias current
switches direction at approximately 1.5 V below the positive
rail. At voltages below this level, the bias current flows out of
the ADA4091-2, from the PNP input stage. Above this voltage,
however, the bias current enters the device, due to the NPN
stage. The actual mechanism within the amplifier for switching
between the input stages comprises Transistor Q3, Transistor Q4,
and Transistor Q7. As the input common-mode voltage
increases, the emitters of Q1 and Q2 follow that voltage plus
a diode drop. Eventually, the emitters of Q1 and Q2 are high
enough to turn on Q3, which diverts the tail current away from
the PNP input stage, turning it off. Instead, the current is
mirrored through Q4 and Q7 to activate the NPN input stage.
As the output voltage approaches either the positive or negative
rail, these transistors begin to saturate. Thus, the final limit
on output voltage is the saturation voltage of these transistors,
which is about 50 mV. The output stage does have inherent gain
arising from the collectors and any external load impedance.
Because of this, the open-loop gain of the op amp is dependent
on the load resistance.
–IN
Q32
Q3
Q16
Q5 Q6
Q1 Q2
Q8
Q9
Q10
Q11
Q12
Q13
Q14
Q15
Q18
Q4
Q17
Q19
Q33
07671-024
+IN
Q7
Figure 37. Simplified Schematic without Input Protection (see Figure 39)
Rev. 0 | Page 13 of 16
ADA4091-2
INPUT OVERVOLTAGE PROTECTION
The ADA4091-2 has two different ESD circuits for enhanced
protection as shown in Figure 39. One circuit is a series resistor
of 5 kΩ to the internal inputs and diodes (D1 and D2 or D5
and D6) from the internal inputs to the supply rails. The other
protection circuit is a circuit with two DIACs (D3 and D4 or D7
and D8) to the supply rails. A DIAC can be considered a bidirectional Zener diode with a transfer characteristic as shown
in Figure 39.
5
The flatband voltage noise of the ADA4091-2 is approximately
24 nV/√Hz, and a 5 kΩ resistor has a noise of 9 nV/√Hz. Adding an additional 5 kΩ resistor increases the total noise by less
than 15% root-sum-square (RSS). Therefore, resistor values
should be kept below this value if overall noise performance is
critical.
Note that this is input protection under abnormal conditions
only. The correct amplifier operation is only specified with an
input voltage range as shown in the Specifications section of
this data sheet.
4
3
CURRENT (mA)
Additional resistance can be added externally in series with
each input to protect against higher peak voltages, however the
additional thermal noise of the resistors must be considered.
2
1
0
–1
V+
–3
–50
–40
–30
–20
–10
0
10
20
30
40
50
VOLTAGE (V)
07671-100
–2
Figure 38. DIAC Transfer Characteristic
D3 R1
D7 R2
D8
For a worst-case design analysis, consider two cases. The
ADA4091-2 has the normal ESD structure from the internal op
amp inputs to the supply rails. In addition, it has 42 V DIACs
from the external inputs to the rails as shown in Figure 37.
D2
D5
D6
D1
D4
V–
•
•
Condition 1. Consider, for example, that when operating
on ±15 V, the inputs can go +42 V above the negative
supply rail. With the –V pin equal to −15 V, +42 V above
this supply (the negative supply) is +27 V,
Condition 2. There is also a restriction on the input current
of 5 mA through a 5 kΩ resistor to the ESD structure to
the positive rail. In Condition 1, +27 V through the 5 kΩ
resistor to +15 V gives a current of 2.4 mA. Thus, the
DIAC is the limiting factor. If the ADA4091-2 supply
voltages are changed to ±5 V, then −5 V + 42 V = 37 V.
However, +5 V + (5 kΩ × 5 mA) = 30 V. Thus, the normal
resistor-diode structure is the limitation when running on
lower supply voltages.
Rev. 0 | Page 14 of 16
07671-023
Therefore, two conditions have to be considered to determine
which one is the limiting factor.
Figure 39. Complete Input Protection Network
ADA4091-2
OUTLINE DIMENSIONS
5.00 (0.1968)
4.80 (0.1890)
8
1
5
4
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
COPLANARITY
0.10
SEATING
PLANE
6.20 (0.2441)
5.80 (0.2284)
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.31 (0.0122)
0.50 (0.0196)
0.25 (0.0099)
45°
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.
012407-A
4.00 (0.1574)
3.80 (0.1497)
Figure 40. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model
ADA4091-2ARZ-R2 1
ADA4091-2ARZ-R71
ADA4091-2ARZ-RL1
1
Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Package Description
8-Lead Standard Small Outline Package [SOIC_N]
8-Lead Standard Small Outline Package [SOIC_N]
8-Lead Standard Small Outline Package [SOIC_N]
Z = RoHS Compliant Part.
Rev. 0 | Page 15 of 16
Package Option
R-8
R-8
R-8
ADA4091-2
NOTES
©2008 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D07671-0-10/08(0)
Rev. 0 | Page 16 of 16