AD AD8629

Zero-Drift, Single-Supply, Rail-to-Rail
Input/Output Operational Amplifier
AD8628/AD8629
Automotive sensors
Pressure and position sensors
Strain gage amplifiers
Medical instrumentation
Thermocouple amplifiers
Precision current sensing
Photodiode amplifier
V– 2
AD8628
5
V+
4
–IN
TOP VIEW
(Not to Scale)
+IN 3
02735-001
OUT 1
Figure 1. 5-Lead TSOT (UJ-5)
and 5-Lead SOT-23 (RT-5)
NC 1
–IN 2
AD8628
+IN 3
TOP VIEW
V– 4 (Not to Scale)
8
NC
7
V+
6
OUT
5
NC
NC = NO CONNECT
02735-002
APPLICATIONS
PIN CONFIGURATIONS
Figure 2. 8-Lead SOIC (R-8)
OUT A 1
–IN A 2
AD8629
8
V+
7
OUT B
+IN A 3
6 –IN B
TOP VIEW
V– 4 (Not to Scale) 5 +IN B
02735-063
Lowest auto-zero amplifier noise
Low offset voltage: 1 µV
Input offset drift: 0.002 µV/°C
Rail-to-rail input and output swing
5 V single-supply operation
High gain, CMRR, and PSRR: 120 dB
Very low input bias current: 100 pA max
Low supply current: 1.0 mA
Overload recovery time: 10 µs
No external components required
Figure 3. 8-Lead SOIC (R-8)
OUT A 1
–IN A 2
AD8629
+IN A 3
TOP VIEW
(Not to Scale)
V– 4
8
V+
7
OUT B
6
–IN B
5
+IN B
02735-064
FEATURES
Figure 4. 8-Lead MSOP (RM-8)
GENERAL DESCRIPTION
This new breed of amplifier has ultralow offset, drift, and bias
current. The AD8628/AD8629 are wide bandwidth auto-zero
amplifiers featuring rail-to-rail input and output swings and low
noise. Operation is fully specified from 2.7 V to 5 V single
supply (±1.35 V to ±2.5 V dual supply).
The AD8628/AD8629 provide benefits previously found only in
expensive auto-zeroing or chopper-stabilized amplifiers. Using
Analog Devices’ new topology, these zero-drift amplifiers
combine low cost with high accuracy and low noise. (No external capacitor is required.) In addition, the AD8628/AD8629
greatly reduce the digital switching noise found in most
chopper-stabilized amplifiers.
With an offset voltage of only 1 µV, drift of less than
0.005 µV/°C, and noise of only 0.5 µV p-p (0 Hz to 10 Hz),
the AD8628/AD8629 are perfectly suited for applications in
which error sources cannot be tolerated. Position and pressure
sensors, medical equipment, and strain gage amplifiers benefit
greatly from nearly zero drift over their operating temperature
range. Many systems can take advantage of the rail-to-rail input
and output swings provided by the AD8628/AD8629 to reduce
input biasing complexity and maximize SNR.
The AD8628/AD8629 are specified for the extended industrial
temperature range (−40°C to +125°C). The AD8628 is available
in tiny TSOT-23, SOT-23, and the popular 8-lead narrow SOIC
plastic packages. The AD8629 is available in the standard 8-lead
narrow SOIC and MSOP plastic packages.
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703
© 2004 Analog Devices, Inc. All rights reserved.
AD8628/AD8629
TABLE OF CONTENTS
Specifications..................................................................................... 3
Total Integrated Input-Referred Noise for First-Order Filter15
Electrical Characteristics ............................................................. 3
Input Overvoltage Protection ................................................... 16
Absolute Maximum Ratings............................................................ 5
Output Phase Reversal............................................................... 16
ESD Caution.................................................................................. 5
Overload Recovery Time .......................................................... 16
Typical Performance Characteristics ............................................. 6
Infrared Sensors.......................................................................... 17
Functional Description .................................................................. 14
Precision Current Shunts .......................................................... 18
1/f Noise....................................................................................... 14
Output Amplifier for High Precision DACs ........................... 18
Peak-to-Peak Noise .................................................................... 15
Outline Dimensions ....................................................................... 19
Noise Behavior with First-Order Low-Pass Filter.................. 15
Ordering Guide .......................................................................... 20
REVISION HISTORY
10/04—Data Sheet Changed from Rev. B to Rev. C
Updated Formatting ...........................................................Universal
Added AD8629....................................................................Universal
Added SOIC and MSOP Pin Configurations ............................... 1
Added Figure 48.............................................................................. 13
Changes to Figure 62...................................................................... 17
Added MSOP Package ................................................................... 19
Changes to Ordering Guide .......................................................... 20
10/03—Data Sheet Changed from Rev. A to Rev. B
Changes to General Description .................................................... 1
Changes to Absolute Maximum Ratings ....................................... 4
Changes to Ordering Guide ............................................................ 4
Added TSOT-23 Package............................................................... 15
6/03—Data Sheet Changed from Rev. 0 to Rev. A
Changes to Specifications ................................................................ 3
Changes to Ordering Guide ............................................................ 4
Change to Functional Description ............................................... 10
Updated Outline Dimensions ....................................................... 15
10/02—Revision 0: Initial Version
Rev. C | Page 2 of 20
AD8628/AD8629
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
VS = 5.0 V, VCM = 2.5 V, TA = 25°C, unless otherwise noted.
Table 1.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Symbol
Conditions
Min
VOS
Typ
Max
Unit
1
5
10
100
1.5
200
250
5
µV
µV
pA
nA
pA
pA
V
dB
dB
dB
dB
µV/°C
−40°C ≤ TA ≤ +125°C
Input Bias Current
IB
30
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
50
−40°C ≤ TA ≤ +125°C
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large Signal Voltage Gain1
AVO
Offset Voltage Drift
OUTPUT CHARACTERISTICS
Output Voltage High
∆VOS/∆T
VOH
Output Voltage Low
VOL
Short-Circuit Limit
ISC
VCM = 0 V to 5 V
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ, VO = 0.3 V to 4.7 V
−40°C ≤ TA ≤ +125°C
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ to ground
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ to ground
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ to V+
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ to V+
−40°C ≤ TA ≤ +125°C
0
120
115
125
120
4.99
4.99
4.95
4.95
±25
−40°C ≤ TA ≤ +125°C
Output Current
IO
−40°C ≤ TA ≤ +125°C
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current/Amplifier
INPUT CAPACITANCE
Differential
Common-Mode
DYNAMIC PERFORMANCE
Slew Rate
Overload Recovery Time
Gain Bandwidth Product
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
Current Noise Density
1
PSRR
ISY
VS = 2.7 V to 5.5 V
−40°C ≤ TA ≤ +125°C
VO = 0 V
−40°C ≤ TA ≤ +125°C
CIN
SR
4.996
4.995
4.98
4.97
1
2
10
15
±50
±40
±30
±15
130
0.85
1.0
0.02
5
5
20
20
1.1
1.2
V
V
V
V
mV
mV
mV
mV
mA
mA
mA
mA
dB
mA
mA
1.5
10
pF
pF
RL = 10 kΩ
1.0
0.05
2.5
V/µs
ms
MHz
0.1 Hz to 10 Hz
0.1 Hz to 1.0 Hz
f = 1 kHz
f = 10 Hz
0.5
0.16
22
5
µV p-p
mV p-p
nV/√Hz
fA/√Hz
GBP
en p-p
en p-p
en
in
115
140
130
145
135
0.002
Gain testing is highly dependent upon test bandwidth.
Rev. C | Page 3 of 20
AD8628/AD8629
VS = 2.7 V, VCM = 1.35 V, VO = 1.4 V, TA = 25°C, unless otherwise noted.
Table 2.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Symbol
Conditions
Min
VOS
Typ
Max
Unit
1
5
10
100
1.5
200
250
5
µV
µV
pA
nA
pA
pA
V
dB
dB
dB
dB
µV/°C
−40°C ≤ TA ≤ +125°C
Input Bias Current
IB
30
1.0
50
−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
Offset Voltage Drift
OUTPUT CHARACTERISTICS
Output Voltage High
∆VOS/∆T
VOH
Output Voltage Low
VOL
Short-Circuit Limit
ISC
VCM = 0 V to 2.7 V
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ , VO = 0.3 V to 2.4 V
−40°C ≤ TA ≤ +125°C
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ to ground
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ to ground
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ to V+
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ to V+
−40°C ≤ TA ≤ +125°C
0
115
110
110
105
2.68
2.68
2.67
2.67
±10
−40°C ≤ TA ≤ +125°C
Output Current
IO
−40°C ≤ TA ≤ +125°C
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current/Amplifier
INPUT CAPACITANCE
Differential
Common-Mode
DYNAMIC PERFORMANCE
Slew Rate
Overload Recovery Time
Gain Bandwidth Product
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
Current Noise Density
PSRR
ISY
VS = 2.7 V to 5.5 V
−40°C ≤ TA ≤ +125°C
VO = 0 V
−40°C ≤ TA ≤ +125°C
CIN
SR
2.695
2.695
2.68
2.675
1
2
10
15
±15
±10
±10
±5
130
0.75
0.9
0.02
5
5
20
20
1.0
1.2
V
V
V
V
mV
mV
mV
mV
mA
mA
mA
mA
dB
mA
mA
1.5
10
pF
pF
RL = 10 kΩ
1
0.05
2
V/µs
ms
MHz
0.1 Hz to 10 Hz
f = 1 kHz
f = 10 Hz
0.5
22
5
µV p-p
nV/√Hz
fA/√Hz
GBP
en p-p
en
in
115
130
120
140
130
0.002
Rev. C | Page 4 of 20
AD8628/AD8629
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameters
Supply Voltage
Input Voltage
Differential Input Voltage1
Output Short-Circuit Duration to GND
Storage Temperature Range
R, RM, RT, UJ Packages
Operating Temperature Range
Junction Temperature Range
R, RM, RT, UJ Packages
Lead Temperature Range
(Soldering, 60 s)
1
Ratings
6V
GND − 0.3 V to VS− + 0.3 V
±5.0 V
Indefinite
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 listed in the operational sections
of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
−65°C to +150°C
−40°C to +125°C
Table 4. Thermal Characteristics
Package Type
5-Lead TSOT-23 (UJ-5)
5-Lead SOT-23 (RT-5)
8-Lead SOIC (R-8)
8-Lead MSOP (RM-8)
−65°C to +150°C
300°C
Differential input voltage is limited to ±5 V or the supply voltage, whichever
is less.
1
θJA1
207
230
158
190
θJC
61
146
43
44
Unit
°C/W
°C/W
°C/W
°C/W
θJA is specified for worst-case conditions, that is, θJA is specified for the device
soldered in a circuit board for surface-mount packages.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. C | Page 5 of 20
AD8628/AD8629
TYPICAL PERFORMANCE CHARACTERISTICS
180
100
VS = 2.7V
TA = 25°C
VS = 5V
VCM = 2.5V
TA = 25°C
90
80
140
NUMBER OF AMPLIFIERS
120
100
80
60
40
70
60
50
40
30
20
0
–2.5
–1.5
–0.5
0.5
INPUT OFFSET VOLTAGE (µV)
1.5
10
0
–2.5
2.5
Figure 5. Input Offset Voltage Distribution at 2.7 V
–1.5
1.5
2.5
7
+85°C
NUMBER OF AMPLIFIERS
40
30
20
+25°C
10
0
1
2
3
4
5
INPUT COMMON-MODE VOLTAGE (V)
5
4
3
2
1
02735-004
–40°C
0
VS = 5V
TA = –40°C TO +125°C
6
50
02735-007
VS = 5V
0
6
0
2
Figure 6. Input Bias Current vs. Input Common-Mode Voltage at 5 V
4
6
TCVOS (nV/°C)
8
10
1
10
Figure 9. Input Offset Voltage Drift
1500
1k
VS = 5V
VS = 5V
TA = 25°C
150°C
1000
100
125°C
OUTPUT VOLTAGE (mV)
INPUT BIAS CURRENT (pA)
–0.5
0.5
INPUT OFFSET VOLTAGE (µV)
Figure 8. Input Offset Voltage Distribution at 5 V
60
INPUT BIAS CURRENT (pA)
02735-006
02735-003
20
500
0
–500
10
SOURCE
SINK
1
0.1
02735-005
–1000
–1500
0
1
2
3
4
5
INPUT COMMON-MODE VOLTAGE (V)
0.01
0.0001
6
Figure 7. Input Bias Current vs. Input Common-Mode Voltage at 5 V
02735-008
NUMBER OF AMPLIFIERS
160
0.001
0.01
0.1
LOAD CURRENT (mA)
Figure 10. Output Voltage to Supply Rail vs. Load Current at 5 V
Rev. C | Page 6 of 20
AD8628/AD8629
1k
1000
TA = 25°C
VS = 2.7V
800
SUPPLY CURRENT (µA)
10
SOURCE
SINK
1
0.1
600
400
0.01
0.0001
0.001
0.01
0.1
LOAD CURRENT (mA)
1
02735-012
02735-009
200
0
10
0
Figure 11. Output Voltage to Supply Rail vs. Load Current at 2.7 V
02735-010
–25
0
25
50
75
100
TEMPERATURE (°C)
125
150
0
30
45
20
90
10
135
0
180
–10
225
–20
–30
10k
175
PHASE SHIFT (Degrees)
40
02735-013
OPEN-LOOP GAIN (dB)
INPUT BIAS CURRENT (pA)
50
100
100k
1M
FREQUENCY (Hz)
10M
Figure 15. Open-Loop Gain and Phase vs. Frequency
Figure 12. Input Bias Current vs. Temperature
70
1250
TA = 25°C
VS = 5V
CL = 20pF
RL = ∞
φM = 52.1°
60
5V
50
2.7V
750
500
02735-011
250
0
50
100
TEMPERATURE (°C)
150
40
0
30
45
20
90
10
135
0
180
–10
225
02735-014
OPEN-LOOP GAIN (dB)
1000
SUPPLY CURRENT (µA)
6
VS = 2.7V
CL = 20pF
RL = ∞
φM = 52.1°
60
450
0
–50
5
70
VS = 5V
VCM = 2.5V
TA = –40°C TO +150°C
900
0
–50
2
3
4
SUPPLY VOLTAGE (V)
Figure 14. Supply Current vs. Supply Voltage
1500
1150
1
–20
–30
10k
200
Figure 13. Supply Current vs. Temperature
100k
1M
FREQUENCY (Hz)
10M
Figure 16. Open-Loop Gain and Phase vs. Frequency
Rev. C | Page 7 of 20
PHASE SHIFT (Degrees)
OUTPUT VOLTAGE (mV)
100
AD8628/AD8629
70
300
VS = 2.7V
CL = 20pF
RL = 2kΩ
60
VS = 5V
270
240
OUTPUT IMPEDANCE (Ω)
40
AV = 100
30
20
AV = 10
10
0
AV = 1
AV = 100
150
120
90
AV = 10
60
–20
–30
1k
AV = 1
180
02735-015
–10
210
10k
100k
1M
FREQUENCY (Hz)
02735-018
CLOSED-LOOP GAIN (dB)
50
30
0
100
10M
Figure 17. Closed-Loop Gain vs. Frequency at 2.7 V
1k
10k
100k
1M
FREQUENCY (Hz)
10M
100M
Figure 20. Output Impedance vs. Frequency at 5 V
70
VS = 5V
CL = 20pF
RL = 2kΩ
60
AV = 100
40
VOLTAGE (500mV/DIV)
CLOSED-LOOP GAIN (dB)
50
30
AV = 10
20
10
AV = 1
0
VS = ±1.35V
CL = 300pF
RL = ∞
AV = 1
02735-016
02735-019
–10
–20
–30
1k
10k
100k
1M
FREQUENCY (Hz)
10M
TIME (4µs/DIV)
Figure 21. Large Signal Transient Response at 2.7 V
Figure 18. Closed-Loop Gain vs. Frequency at 5 V
300
VS = 2.7V
270
VOLTAGE (1V/DIV)
AV = 1
210
180
AV = 100
150
120
VS = ±2.5V
CL = 300pF
RL = ∞
AV = 1
90
30
0
100
02735-020
AV = 10
60
02735-017
OUTPUT IMPEDANCE (Ω)
240
1k
10k
100k
1M
FREQUENCY (Hz)
10M
100M
TIME (5µs/DIV)
Figure 22. Large Signal Transient Response at 5 V
Figure 19. Output Impedance vs. Frequency at 2.7 V
Rev. C | Page 8 of 20
AD8628/AD8629
80
VS = ±1.35V
CL = 50pF
RL = ∞
AV = 1
VS = ±2.5V
RL = 2kΩ
TA = 25°C
70
OVERSHOOT (%)
VOLTAGE (50mV/DIV)
60
50
40
30
OS–
20
02735-021
OS+
02735-024
10
0
1
TIME (4µs/DIV)
Figure 23. Small Signal Transient Response at 2.7 V
10
100
CAPACITIVE LOAD (pF)
1k
Figure 26. Small Signal Overshoot vs. Load Capacitance at 5 V
VS = ±2.5V
CL = 50pF
RL = ∞
AV = 1
VS = ±2.5V
AV = –50
RL = 10kΩ
CL = 0
CH1 = 50mV/DIV
CH2 = 1V/DIV
0V
0V
02735-025
02735-022
VOLTAGE (V)
VOLTAGE (50mV/DIV)
VIN
VOUT
TIME (4µs/DIV)
TIME (2µs/DIV)
Figure 27. Positive Overvoltage Recovery
Figure 24. Small Signal Transient Response at 5 V
100
VS = ±1.35V
RL = 2kΩ
TA = 25°C
90
0V
VS = ±2.5V
AV = –50
RL = 10kΩ
CL = 0
CH1 = 50mV/DIV
CH2 = 1V/DIV
80
VOLTAGE (V)
60
OS–
50
40
VIN
VOUT
OS+
30
20
10
0
1
10
100
CAPACITIVE LOAD (pF)
1k
02735-026
0V
02735-023
OVERSHOOT (%)
70
TIME (10µs/DIV)
Figure 28. Negative Overvoltage Recovery
Figure 25. Small Signal Overshoot vs. Load Capacitance at 2.7 V
Rev. C | Page 9 of 20
AD8628/AD8629
140
VS = ±2.5V
VIN = 1kHz @ ±3V p-p
CL = 0pF
RL = 10kΩ
AV = 1
VS = ±1.35V
120
100
PSRR (dB)
VOLTAGE (1V/DIV)
80
60
+PSRR
40
20
–PSRR
0
–40
–60
100
TIME (200µs/DIV)
140
120
100
100
80
80
60
60
PSRR (dB)
120
40
20
–20
–40
1M
10M
–PSRR
–40
–60
100
10M
1k
10k
100k
FREQUENCY (Hz)
Figure 33. PSRR vs. Frequency
Figure 30. CMRR vs. Frequency at 2.7 V
3.0
140
VS = 5V
VS = 2.7V
RL = 10kΩ
TA = 25°C
AV = 1
2.5
OUTPUT SWING (V p-p)
100
80
60
40
20
0
–20
2.0
1.5
1.0
–40
1k
10k
100k
FREQUENCY (Hz)
1M
0
100
10M
02735-032
0.5
02735-029
CMRR (dB)
1M
VS = ±2.5V
20
–20
–60
100
10M
+PSRR
0
120
1M
40
0
02735-028
CMRR (dB)
VS = 2.7V
10k
100k
FREQUENCY (Hz)
10k
100k
FREQUENCY (Hz)
02735-031
140
1k
1k
Figure 32. PSRR vs. Frequency
Figure 29. No Phase Reversal
–60
100
02735-030
02735-027
–20
1k
10k
FREQUENCY (Hz)
100k
Figure 34. Maximum Output Swing vs. Frequency
Figure 31. CMRR vs. Frequency at 5 V
Rev. C | Page 10 of 20
1M
AD8628/AD8629
5.5
120
VS = 2.7V
NOISE AT 1kHz = 21.3nV
5.0
4.0
3.5
3.0
2.5
2.0
1.5
0.5
0
100
1k
10k
FREQUENCY (Hz)
100k
90
75
60
45
30
15
02735-033
1.0
105
02735-036
OUTPUT SWING (V p-p)
4.5
VOLTAGE NOISE DENSITY (nV/√Hz)
VS = 5V
RL = 10kΩ
TA = 25°C
AV = 1
0
1M
0
Figure 35. Maximum Output Swing vs. Frequency at 5 V
2.0
2.5
120
VS = 2.7V
VOLTAGE NOISE DENSITY (nV/√Hz)
0.30
0.15
0
–0.15
–0.30
–0.60
0
1
2
3
4
5
6
TIME (µs)
7
8
9
90
75
60
45
30
15
02735-034
–0.45
VS = 2.7V
NOISE AT 10kHz = 42.4nV
105
02735-037
0.45
VOLTAGE (µV)
1.0
1.5
FREQUENCY (kHz)
Figure 38. Voltage Noise Density at 2.7 V from 0 Hz to 2.5 kHz
0.60
0
10
0
Figure 36. 0.1 Hz to 10 Hz Noise at 2.7 V
5
10
15
FREQUENCY (kHz)
20
25
Figure 39. Voltage Noise Density at 2.7 V from 0 Hz to 25 kHz
0.60
120
VS = 5V
VOLTAGE NOISE DENSITY (nV/√Hz)
0.30
0.15
0
–0.15
–0.30
–0.60
0
1
2
3
4
5
6
TIME (µs)
7
8
9
90
75
60
45
30
15
02735-035
–0.45
VS = 5V
NOISE AT 1kHz = 22.1nV
105
02735-038
0.45
VOLTAGE (µV)
0.5
0
10
0
Figure 37. 0.1 Hz to 10 Hz Noise at 5 V
0.5
1.0
1.5
FREQUENCY (kHz)
2.0
Figure 40. Voltage Noise Density at 5 V from 0 Hz to 2.5 kHz
Rev. C | Page 11 of 20
2.5
AD8628/AD8629
150
105
90
75
60
45
30
02735-039
15
0
0
5
10
15
FREQUENCY (kHz)
20
VS = 2.7V
TA = –40°C TO +150°C
100
50
ISC–
0
ISC+
–50
–100
–50
25
Figure 41. Voltage Noise Density at 5 V from 0 Hz to 25 kHz
–25
0
25
50
75
100
TEMPERATURE (°C)
125
150
175
Figure 44. Output Short-Circuit Current vs. Temperature
120
150
90
75
60
45
30
02735-040
15
0
0
5
FREQUENCY (kHz)
VS = 5V
TA = –40°C TO +150°C
100
ISC–
50
0
–50
ISC+
–100
–50
10
02735-043
105
OUTPUT SHORT-CIRCUIT CURRENT (mA)
VS = 5V
VOLTAGE NOISE DENSITY (nV/√Hz)
02735-042
VS = 5V
NOISE AT 10kHz = 36.4nV
OUTPUT SHORT-CIRCUIT CURRENT (mA)
VOLTAGE NOISE DENSITY (nV/√Hz)
120
–25
0
25
50
75
100
TEMPERATURE (°C)
125
150
175
Figure 45. Output Short-Circuit Current vs. Temperature
Figure 42. Voltage Noise
1k
150
VS = 5V
VS = 2.7V TO 5V
TA = –40°C TO +125°C
120
110
100
90
80
70
60
50
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
VCC – VOH @ 1kΩ
100
VOL – VEE @ 1kΩ
VCC – VOH @ 10kΩ
10
VOL – VEE @ 10kΩ
VCC – VOH @ 100kΩ
1
VOL – VEE @ 100kΩ
0.10
–50
125
Figure 43. Power Supply Rejection vs. Temperature
02735-044
OUTPUT-TO-RAIL VOLTAGE (mV)
130
02735-041
POWER SUPPLY REJECTION (dB)
140
–25
0
25
50
75
100
TEMPERATURE (°C)
125
150
Figure 46. Output-to-Rail Voltage vs. Temperature
Rev. C | Page 12 of 20
175
AD8628/AD8629
140
1k
VSY = ±2.5V
120
VOL – VEE @ 1kΩ
VCC – VOH @ 10kΩ
10
VCC – VOH @ 100kΩ
1
VOL – VEE @ 10kΩ
VOL – VEE @ 100kΩ
0.10
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
125
150
100
80
60
40
R1
10kΩ
+2.5V
VIN
28mV p-p
+
–
20
R2
100Ω
V–
V+
A
B
V–
VOUT
V+
02735-062
CHANNEL SEPARATION (dB)
VCC – VOH @ 1kΩ
100
02735-045
OUTPUT-TO-RAIL VOLTAGE (mV)
VS = 2.7V
–2.5V
0
1k
175
10k
100k
FREQUENCY (Hz)
1M
Figure 48. AD8629 Channel Separation
Figure 47. Output-to-Rail Voltage vs. Temperature
Rev. C | Page 13 of 20
10M
AD8628/AD8629
FUNCTIONAL DESCRIPTION
The AD8628/AD8629 are single-supply, ultrahigh precision
rail-to-rail input and output operational amplifiers. The typical
offset voltage of less than 1 µV allows these amplifiers to be
easily configured for high gains without risk of excessive
output voltage errors. The extremely small temperature drift of
2 nV/°C ensures a minimum of offset voltage error over their
entire temperature range of −40°C to +125°C, making these
amplifiers ideal for a variety of sensitive measurement
applications in harsh operating environments.
1/F NOISE
The AD8628/AD8629 achieve a high degree of precision
through a patented combination of auto-zeroing and chopping.
This unique topology allows the AD8628/AD8629 to maintain
their low offset voltage over a wide temperature range and over
their operating lifetime. The AD8628/AD8629 also optimize the
noise and bandwidth over previous generations of auto-zero
amplifiers, offering the lowest voltage noise of any auto-zero
amplifier by more than 50%.
The internal elimination of 1/f noise is accomplished as follows.
1/f noise appears as a slowly varying offset to AD8628/AD8629
inputs. Auto-zeroing corrects any dc or low frequency offset.
Therefore, the 1/f noise component is essentially removed,
leaving the AD8628/AD8629 free of 1/f noise.
120
Rev. C | Page 14 of 20
LTC2050
(89.7nV/√Hz)
105
90
75
60
LMC2001
(31.1nV/√Hz)
45
30
15
AD8628
(19.4nV/√Hz)
MK AT 1kHz FOR ALL 3 GRAPHS
0
0
2
4
6
FREQUENCY (kHz)
8
10
Figure 49. Noise Spectral Density of AD8628 vs. Competition
02735-046
The AD8628 is among the few auto-zero amplifiers offered in
the 5-lead TSOT-23 package. This provides a significant
improvement over the ac parameters of the previous auto-zero
amplifiers. The AD8628/AD8629 have low noise over a
relatively wide bandwidth (0 Hz to 10 kHz) and can be used
where the highest dc precision is required. In systems with
signal bandwidths of from 5 kHz to 10 kHz, the AD8628/
AD8629 provide true 16-bit accuracy, making them the best
choice for very high resolution systems.
One of the biggest advantages that the AD8628/AD8629 bring
to systems applications over competitive auto-zero amplifiers is
their very low noise. The comparison shown in Figure 49
indicates an input-referred noise density of 19.4 nV/√Hz at
1 kHz for the AD8628, which is much better than the LTC2050
and LMC2001. The noise is flat from dc to 1.5 kHz, slowly
increasing up to 20 kHz. The lower noise at low frequency is
desirable where auto-zero amplifiers are widely used.
VOLTAGE NOISE DENSITY (nV/√Hz)
Previous designs used either auto-zeroing or chopping to add
precision to the specifications of an amplifier. Auto-zeroing
results in low noise energy at the auto-zeroing frequency, at the
expense of higher low-frequency noise due to aliasing of
wideband noise into the auto-zeroed frequency band. Chopping
results in lower low-frequency noise at the expense of larger
noise energy at the chopping frequency. The AD8628/AD8629
family use both auto-zeroing and chopping in a patented pingpong arrangement to obtain lower low-frequency noise together
with lower energy at the chopping and auto-zeroing
frequencies, maximizing the signal-to-noise ratio (SNR) for the
majority of applications without the need for additional
filtering. The relatively high clock frequency of 15 kHz
simplifies filter requirements for a wide, useful, noise-free
bandwidth.
1/f noise, also known as pink noise, is a major contributor to
errors in dc-coupled measurements. This 1/f noise error term
can be in the range of several µV or more, and, when amplified
with the closed-loop gain of the circuit, can show up as a large
output offset. For example, when an amplifier with a 5 µV p-p
1/f noise is configured for a gain of 1,000, its output has 5 mV
of error due to the 1/f noise. But the AD8628/AD8629 eliminate
1/f noise internally, and thereby greatly reduce output errors.
12
AD8628/AD8629
50
PEAK-TO-PEAK NOISE
45
Because of the ping-pong action between auto-zeroing and
chopping, the peak-to-peak noise of the AD8628/AD8629 is
much lower than the competition. Figure 50 and Figure 51
show this comparison.
40
NOISE (dB)
35
en p-p = 0.5µV
BW = 0.1Hz TO 10Hz
30
25
20
VOLTAGE (0.5µV/DIV)
15
02735-050
10
5
0
0
10
20
30
40
50
60
FREQUENCY (Hz)
70
80
90
100
Figure 53. Simulation Transfer Function of the Test Circuit
02735-047
50
45
40
TIME (1s/DIV)
35
NOISE (dB)
Figure 50. AD8628 Peak-to-Peak Noise
en p-p = 2.3µV
BW = 0.1Hz TO 10Hz
30
25
20
15
02735-051
VOLTAGE (0.5µV/DIV)
10
5
0
0
10
20
30
40
50
60
70
FREQUENCY (kHz)
80
90
100
Figure 54. Actual Transfer Function of Test Circuit
02735-048
The measured noise spectrum of the test circuit shows that
noise between 5 kHz and 45 kHz is successfully rolled off by the
first-order filter.
TOTAL INTEGRATED INPUT-REFERRED NOISE
FOR FIRST-ORDER FILTER
Figure 51. LTC2050 Peak-to-Peak Noise
NOISE BEHAVIOR WITH FIRST-ORDER LOW-PASS
FILTER
The AD8628 was simulated as a low-pass filter and then
configured as shown in Figure 52. The behavior of the AD8628
matches the simulated data. It was verified that noise is rolled
off by first-order filtering.
IN
OUT
LTC2050
AD8551
Figure 52. Test Circuit: First-Order Low-Pass Filter—×101 Gain
and 3 kHz Corner Frequency
0.1
10
100
1k
3dB FILTER BANDWIDTH (Hz)
Figure 55. 3 dB Filter Bandwidth in Hz
Rev. C | Page 15 of 20
AD8628
1
02735-052
1kΩ
470pF
10
02735-049
100kΩ
For a first-order filter, the total integrated noise from the
AD8628 is lower than the LTC2050.
RMS NOISE (µV)
TIME (1s/DIV)
10k
AD8628/AD8629
INPUT OVERVOLTAGE PROTECTION
These diodes are connected between the inputs and each supply
rail to protect the input transistors against an electrostatic
discharge event and are normally reverse-biased. However, if the
input voltage exceeds the supply voltage, these ESD diodes can
become forward-biased. Without current limiting, excessive
amounts of current could flow through these diodes, causing
permanent damage to the device. If inputs are subject to
overvoltage, appropriate series resistors should be inserted to
limit the diode current to less than 5 mA maximum.
0V
0V
02735-053
VOLTAGE (V)
Although the AD8628/AD8629 are rail-to-rail input amplifiers,
care should be taken to ensure that the potential difference
between the inputs does not exceed the supply voltage. Under
normal negative feedback operating conditions, the amplifier
corrects its output to ensure that the two inputs are at the same
voltage. However, if either input exceeds either supply rail by
more than 0.3 V, large currents begin to flow through the ESD
protection diodes in the amplifier.
CH1 = 50mV/DIV
CH2 = 1V/DIV
AV = –50
VIN
VOUT
TIME (500µs/DIV)
Figure 56. Positive Input Overload Recovery for the AD8628
CH1 = 50mV/DIV
CH2 = 1V/DIV
AV = –50
VIN
0V
0V
02735-054
Output phase reversal occurs in some amplifiers when the input
common-mode voltage range is exceeded. As common-mode
voltage is moved outside of the common-mode range, the
outputs of these amplifiers can suddenly jump in the opposite
direction to the supply rail. This is the result of the differential
input pair shutting down, causing a radical shifting of internal
voltages that results in the erratic output behavior.
VOLTAGE (V)
OUTPUT PHASE REVERSAL
VOUT
The AD8628/AD8629 amplifiers have been carefully designed
to prevent any output phase reversal, provided that both inputs
are maintained within the supply voltages. If one or both inputs
could exceed either supply voltage, a resistor should be placed in
series with the input to limit the current to less than 5 mA. This
ensures that the output does not reverse its phase.
TIME (500µs/DIV)
Figure 57. Positive Input Overload Recovery for LTC2050
CH1 = 50mV/DIV
CH2 = 1V/DIV
AV = –50
VIN
Rev. C | Page 16 of 20
0V
0V
02735-055
Many auto-zero amplifiers are plagued by a long overload
recovery time, often in ms, due to the complicated settling
behavior of the internal nulling loops after saturation of the
outputs. The AD8628/AD8629 have been designed so that
internal settling occurs within two clock cycles after output
saturation happens. This results in a much shorter recovery
time, less than 10 µs, when compared to other auto-zero
amplifiers. The wide bandwidth of the AD8628/AD8629
enhances performance when they are used to drive loads that
inject transients into the outputs. This is a common situation
when an amplifier is used to drive the input of switched
capacitor ADCs.
VOLTAGE (V)
OVERLOAD RECOVERY TIME
VOUT
TIME (500µs/DIV)
Figure 58. Positive Input Overload Recovery for LMC2001
AD8628/AD8629
The results shown in Figure 56 to Figure 61 are summarized in
Table 5.
0V
VOLTAGE (V)
CH1 = 50mV/DIV
CH2 = 1V/DIV
AV = –50
Table 5. Overload Recovery Time
VIN
VOUT
02735-056
0V
Negative Overload
Recovery (µs)
9
25,000
35,000
INFRARED SENSORS
Infrared (IR) sensors, particularly thermopiles, are increasingly
being used in temperature measurement for applications as
wide-ranging as automotive climate control, human ear
thermometers, home insulation analysis, and automotive repair
diagnostics. The relatively small output signal of the sensor
demands high gain with very low offset voltage and drift to
avoid dc errors.
TIME (500µs/DIV)
Figure 59. Negative Input Overload Recovery for the AD8628
0V
CH1 = 50mV/DIV
CH2 = 1V/DIV
AV = –50
VIN
VOUT
0V
02735-057
VOLTAGE (V)
Positive Overload
Recovery (µs)
6
650
40,000
Product
AD8628
LTC2050
LMC2001
If interstage ac coupling is used (Figure 62), low offset and drift
prevents the input amplifier’s output from drifting close to
saturation. The low input bias currents generate minimal errors
from the sensor’s output impedance. As with pressure sensors,
the very low amplifier drift with time and temperature eliminates additional errors once the temperature measurement has
been calibrated. The low 1/f noise improves SNR for dc
measurements taken over periods often exceeding 1/5 s.
Figure 64 (shows a circuit that can amplify ac signals from
100 µV to 300 µV up to the 1 V to 3 V level, with gain of
10,000 for accurate A/D conversion.
TIME (500µs/DIV)
Figure 60. Negative Input Overload Recovery for LTC2050
10kΩ
100Ω
100kΩ
100kΩ
5V
5V
100µV – 300µV
IR
DETECTOR
VIN
VOUT
10µF
1/2 AD8629
1/2 AD8629
10kΩ
fC ≈ 1.6Hz
TO BIAS
VOLTAGE
Figure 62. AD8629 Used as Preamplifier for Thermopile
0V
02735-058
VOLTAGE (V)
CH1 = 50mV/DIV
CH2 = 1V/DIV
AV = –50
TIME (500µs/DIV)
Figure 61. Negative Input Overload Recovery for LMC2001
Rev. C | Page 17 of 20
02735-059
0V
AD8628/AD8629
PRECISION CURRENT SHUNTS
OUTPUT AMPLIFIER FOR HIGH PRECISION DACs
A precision shunt current sensor benefits from the unique
attributes of auto-zero amplifiers when used in a differencing
configuration (Figure 63). Shunt current sensors are used in
precision current sources for feedback control systems. They are
also used in a variety of other applications, including battery
fuel gauging, laser diode power measurement and control,
torque feedback controls in electric power steering, and
precision power metering.
The AD8628/AD8629 are used as output amplifiers for a 16-bit
high precision DAC in a unipolar configuration. In this case, the
selected op amp needs to have very low offset voltage (the DAC
LSB is 38 µV when operated with a 2.5 V reference) to eliminate
the need for output offset trims. Input bias current (typically a
few tens of picoamperes) must also be very low, because it
generates an additional zero code error when multiplied by the
DAC output impedance (approximately 6 kΩ).
SUPPLY
I
100kΩ
e = 1,000 RS I
100mV/mA
RS
0.1Ω
Rail-to-rail input and output provide full-scale output with very
little error. Output impedance of the DAC is constant and codeindependent, but the high input impedance of the AD8628/
AD8629 minimizes gain errors. The amplifiers’ wide bandwidth
also serves well in this case. The amplifiers, with settling time of
1 µs, add another time constant to the system, increasing the
settling time of the output. The settling time of the AD5541 is
1 µs. The combined settling time is approximately 1.4 µs, as can
be derived from the following equation:
RL
100Ω
C
5V
AD8628
100Ω
C
02735-060
100kΩ
t S (TOTAL ) =
(t S DAC )2 + (t S AD8628 )2
Figure 63. Low-Side Current Sensing
5V
2.5V
0.1µF
0.1µF
SERIAL
INTERFACE
Rev. C | Page 18 of 20
VDD
10µF
REF(REF*)
REFS*
CS
DIN
SCLK
AD5541/AD5542
LDAC*
UNIPOLAR
OUTPUT
OUT
AD8628
DGND
AGND
*AD5542 ONLY
Figure 64. AD8628 Used as an Output Amplifier
03023-061
In such applications, it is desirable to use a shunt with very low
resistance to minimize the series voltage drop; this minimizes
wasted power and allows the measurement of high currents
without saving power. A typical shunt might be 0.1 Ω. At
measured current values of 1 A, the shunt’s output signal is
hundreds of mV, or even V, and amplifier error sources are not
critical. However, at low measured current values in the 1 mA
range, the 100 µV output voltage of the shunt demands a very
low offset voltage and drift to maintain absolute accuracy. Low
input bias currents are also needed, so that injected bias current
does not become a significant percentage of the measured
current. High open-loop gain, CMRR, and PSRR all help to
maintain the overall circuit accuracy. As long as the rate of
change of the current is not too fast, an auto-zero amplifier can
be used with excellent results.
AD8628/AD8629
OUTLINE DIMENSIONS
2.90 BSC
5
5.00 (0.1968)
4.80 (0.1890)
4
2.80 BSC
1.60 BSC
8
1
2
5
4.00 (0.1574)
3.80 (0.1497) 1
3
6.20 (0.2440)
4 5.80 (0.2284)
PIN 1
0.95 BSC
1.27 (0.0500)
BSC
1.90
BSC
0.90
0.87
0.84
0.25 (0.0098)
0.10 (0.0040)
1.00 MAX
0.10 MAX
0.50
0.30
8°
4°
SEATING
PLANE
0.20
0.08
0.51 (0.0201)
COPLANARITY
SEATING 0.31 (0.0122)
0.10
PLANE
0.60
0.45
0.30
0.50 (0.0196)
× 45°
0.25 (0.0099)
1.75 (0.0688)
1.35 (0.0532)
8°
0.25 (0.0098) 0° 1.27 (0.0500)
0.40 (0.0157)
0.17 (0.0067)
COMPLIANT TO JEDEC STANDARDS MO-193AB
COMPLIANT TO JEDEC STANDARDS MS-012AA
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 65. 5-Lead Thin Small Outline Transistor Package [TSOT]
(UJ-5)
Dimensions shown in millimeters
Figure 67. 8-Lead Standard Small Outline Package [SOIC]
Narrow Body (R-8)
Dimensions shown in millimeters and (inches)
2.90 BSC
3.00
BSC
5
4
2.80 BSC
1.60 BSC
8
1
2
3
5
4.90
BSC
3.00
BSC
PIN 1
4
0.95 BSC
1.90
BSC
1.30
1.15
0.90
PIN 1
0.65 BSC
1.45 MAX
0.15 MAX
0.50
0.30
SEATING
PLANE
1.10 MAX
0.15
0.00
0.22
0.08
10°
5°
0°
0.60
0.45
0.30
0.38
0.22
COPLANARITY
0.10
0.23
0.08
8°
0°
0.80
0.60
0.40
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS MO-178AA
COMPLIANT TO JEDEC STANDARDS MO-187AA
Figure 66. 5-Lead Small Outline Transistor Package [SOT-23]
(RT-5)
Dimensions shown in millimeters
Figure 65. 8-Lead Standard Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
Rev. C | Page 19 of 20
AD8628/AD8629
ORDERING GUIDE
Model
AD8628AUJ-R2
AD8628AUJ-REEL
AD8628AUJ-REEL7
AD8628AUJZ-R21
AD8628AUJZ-REEL1
AD8628AUJZ-REEL71
AD8628AR
AD8628AR-REEL
AD8628AR-REEL7
AD8628ARZ1
AD8628ARZ-REEL1
AD8628ARZ-REEL71
AD8628ART-R2
AD8628ART-REEL7
AD8628ARTZ-R21
AD8628ARTZ-REEL71
AD8629ARZ1
AD8629ARZ-REEL1
AD8629ARZ-REEL71
AD8629ARMZ-R21
AD8629ARMZ-REEL1
1
Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Package Description
5-Lead TSOT-23
5-Lead TSOT-23
5-Lead TSOT-23
5-Lead TSOT-23
5-Lead TSOT-23
5-Lead TSOT-23
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
5-Lead SOT-23
5-Lead SOT-23
5-Lead SOT-23
5-Lead SOT-23
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead MSOP
8-Lead MSOP
Z = Pb-free part.
© 2004 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
C02735–0–10/04(C)
Rev. C | Page 20 of 20
Package Option
UJ-5
UJ-5
UJ-5
UJ-5
UJ-5
UJ-5
R-8
R-8
R-8
R-8
R-8
R-8
RT-5
RT-5
RT-5
RT-5
R-8
R-8
R-8
RM-8
RM-8
Branding
AYB
AYB
AYB
AYB
AYB
AYB
AYA
AYA
AYA
AYA
A06
A06