Zero-Drift, Single-Supply, Rail-to-Rail
Input/Output Operational Amplifier
AD8628/AD8629
Rev. C
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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
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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.
FEATURES
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
APPLICATIONS
Automotive sensors
Pressure and position sensors
Strain gage amplifiers
Medical instrumentation
Thermocouple amplifiers
Precision current sensing
Photodiode amplifier
PIN CONFIGURATIONS
OUT
1
V–
2
+IN
3
V+
5
–IN
4
AD8628
TOP VIEW
(Not to Scale)
02735-001
Figure 1. 5-Lead TSOT (UJ-5)
and 5-Lead SOT-23 (RT-5)
NC
1
–IN
2
+IN
3
V–
4
NC
8
V+
7
OUT
6
NC
5
NC = NO CONNECT
AD8628
TOP VIEW
(Not to Scale)
02735-002
Figure 2. 8-Lead SOIC (R-8)
OUT A
1
–IN A
2
+IN A
3
V–
4
V+
8
OUT B
7
–IN B
6
+IN B
5
AD8629
TOP VIEW
(Not to Scale)
02735-063
Figure 3. 8-Lead SOIC (R-8)
O
UT
A
1
–IN A
2
+IN A
3
V–
4
V+
8
OUT B
7
–IN B
6
+IN B
5
AD8629
TOP VIEW
(Not to Scale)
02735-064
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 exter-
nal 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.
AD8628/AD8629
Rev. C | Page 2 of 20
TABLE OF CONTENTS
Specifications..................................................................................... 3
Electrical Characteristics............................................................. 3
Absolute Maximum Ratings............................................................ 5
ESD Caution.................................................................................. 5
Typical Performance Characteristics ............................................. 6
Functional Description .................................................................. 14
1/f Noise....................................................................................... 14
Peak-to-Peak Noise .................................................................... 15
Noise Behavior with First-Order Low-Pass Filter.................. 15
Total Integrated Input-Referred Noise for First-Order Filter15
Input Overvoltage Protection................................................... 16
Output Phase Reversal............................................................... 16
Overload Recovery Time .......................................................... 16
Infrared Sensors.......................................................................... 17
Precision Current Shunts .......................................................... 18
Output Amplifier for High Precision DACs........................... 18
Outline Dimensions....................................................................... 19
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
AD8628/AD8629
Rev. C | Page 3 of 20
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
VS = 5.0 V, VCM = 2.5 V, TA = 25°C, unless otherwise noted.
Table 1.
Parameter Symbol Conditions Min Typ Max Unit
INPUT CHARACTERISTICS
Offset Voltage VOS 1 5 µV
−40°C ≤ TA ≤ +125°C 10 µV
Input Bias Current IB 30 100 pA
−40°C ≤ TA ≤ +125°C 1.5 nA
Input Offset Current IOS 50 200 pA
−40°C ≤ TA ≤ +125°C 250 pA
Input Voltage Range 0 5 V
Common-Mode Rejection Ratio CMRR VCM = 0 V to 5 V 120 140 dB
−40°C ≤ TA ≤ +125°C 115 130 dB
Large Signal Voltage Gain1AVO RL = 10 kΩ, VO = 0.3 V to 4.7 V 125 145 dB
−40°C ≤ TA ≤ +125°C 120 135 dB
Offset Voltage Drift ∆VOS/∆T −40°C ≤ TA ≤ +125°C 0.002 0.02 µV/°C
OUTPUT CHARACTERISTICS
Output Voltage High VOH RL = 100 kΩ to ground 4.99 4.996 V
−40°C ≤ TA ≤ +125°C 4.99 4.995 V
R
L = 10 kΩ to ground 4.95 4.98 V
−40°C ≤ TA ≤ +125°C 4.95 4.97 V
Output Voltage Low VOL RL = 100 kΩ to V+ 1 5 mV
−40°C ≤ TA ≤ +125°C 2 5 mV
R
L = 10 kΩ to V+ 10 20 mV
−40°C ≤ TA ≤ +125°C 15 20 mV
Short-Circuit Limit ISC ±25 ±50 mA
−40°C ≤ TA ≤ +125°C ±40 mA
Output Current IO ±30 mA
−40°C ≤ TA ≤ +125°C ±15 mA
POWER SUPPLY
Power Supply Rejection Ratio PSRR VS = 2.7 V to 5.5 V
−40°C ≤ TA ≤ +125°C 115 130 dB
Supply Current/Amplifier ISY VO = 0 V 0.85 1.1 mA
−40°C ≤ TA ≤ +125°C 1.0 1.2 mA
INPUT CAPACITANCE
Differential CIN 1.5 pF
Common-Mode 10 pF
DYNAMIC PERFORMANCE
Slew Rate SR RL = 10 kΩ 1.0 V/µs
Overload Recovery Time 0.05 ms
Gain Bandwidth Product GBP 2.5 MHz
NOISE PERFORMANCE
Voltage Noise en p-p 0.1 Hz to 10 Hz 0.5 µV p-p
e
n p-p 0.1 Hz to 1.0 Hz 0.16 mV p-p
Voltage Noise Density enf = 1 kHz 22 nV/√Hz
Current Noise Density inf = 10 Hz 5 fA/√Hz
1 Gain testing is highly dependent upon test bandwidth.
AD8628/AD8629
Rev. C | Page 4 of 20
VS = 2.7 V, VCM = 1.35 V, VO = 1.4 V, TA = 25°C, unless otherwise noted.
Table 2.
Parameter Symbol Conditions Min Typ Max Unit
INPUT CHARACTERISTICS
Offset Voltage VOS 1 5 µV
−40°C ≤ TA ≤ +125°C 10 µV
Input Bias Current IB 30 100 pA
−40°C ≤ TA ≤ +125°C 1.0 1.5 nA
Input Offset Current IOS 50 200 pA
−40°C ≤ TA ≤ +125°C 250 pA
Input Voltage Range 0 5 V
Common-Mode Rejection Ratio CMRR VCM = 0 V to 2.7 V 115 130 dB
−40°C ≤ TA ≤ +125°C 110 120 dB
Large Signal Voltage Gain AVO RL = 10 kΩ , VO = 0.3 V to 2.4 V 110 140 dB
−40°C ≤ TA ≤ +125°C 105 130 dB
Offset Voltage Drift ∆VOS/∆T −40°C ≤ TA ≤ +125°C 0.002 0.02 µV/°C
OUTPUT CHARACTERISTICS
Output Voltage High VOH RL = 100 kΩ to ground 2.68 2.695 V
−40°C ≤ TA ≤ +125°C 2.68 2.695 V
R
L = 10 kΩ to ground 2.67 2.68 V
−40°C ≤ TA ≤ +125°C 2.67 2.675 V
Output Voltage Low VOL RL = 100 kΩ to V+ 1 5 mV
−40°C ≤ TA ≤ +125°C 2 5 mV
R
L = 10 kΩ to V+ 10 20 mV
−40°C ≤ TA ≤ +125°C 15 20 mV
Short-Circuit Limit ISC ±10 ±15 mA
−40°C ≤ TA ≤ +125°C ±10 mA
Output Current IO ±10 mA
−40°C ≤ TA ≤ +125°C ±5 mA
POWER SUPPLY
Power Supply Rejection Ratio PSRR VS = 2.7 V to 5.5 V
−40°C ≤ TA ≤ +125°C 115 130 dB
Supply Current/Amplifier ISY VO = 0 V 0.75 1.0 mA
−40°C ≤ TA ≤ +125°C 0.9 1.2 mA
INPUT CAPACITANCE
Differential CIN 1.5 pF
Common-Mode 10 pF
DYNAMIC PERFORMANCE
Slew Rate SR RL = 10 kΩ 1 V/µs
Overload Recovery Time 0.05 ms
Gain Bandwidth Product GBP 2 MHz
NOISE PERFORMANCE
Voltage Noise en p-p 0.1 Hz to 10 Hz 0.5 µV p-p
Voltage Noise Density enf = 1 kHz 22 nV/√Hz
Current Noise Density inf = 10 Hz 5 fA/√Hz
AD8628/AD8629
Rev. C | Page 5 of 20
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameters Ratings
Supply Voltage 6 V
Input Voltage GND − 0.3 V to VS− + 0.3 V
Differential Input Voltage1±5.0 V
Output Short-Circuit Duration to GND Indefinite
Storage Temperature Range
R, RM, RT, UJ Packages −65°C to +150°C
Operating Temperature Range −40°C to +125°C
Junction Temperature Range
R, RM, RT, UJ Packages −65°C to +150°C
Lead Temperature Range
(Soldering, 60 s)
300°C
1 Differential input voltage is limited to ±5 V or the supply voltage, whichever
is less.
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.
Table 4. Thermal Characteristics
Package Type θJA1θJC Unit
5-Lead TSOT-23 (UJ-5) 207 61 °C/W
5-Lead SOT-23 (RT-5) 230 146 °C/W
8-Lead SOIC (R-8) 158 43 °C/W
8-Lead MSOP (RM-8) 190 44 °C/W
1 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.
AD8628/AD8629
Rev. C | Page 6 of 20
TYPICAL PERFORMANCE CHARACTERISTICS
INPUT OFFSET VOLTAGE (µV)
NUMBER OF AMPLIFIERS
180
160
140
120
100
80
60
40
20
0
–2.5 –1.5 –0.5 0.5 1.5 2.5
02735-003
V
S
= 2.7V
T
A
= 25°C
Figure 5. Input Offset Voltage Distribution at 2.7 V
+85°C
+25°C
–40°C
V
S
= 5V
INPUT COMMON-MODE VOLTAGE (V)
INPUT BIAS CURRENT (pA)
60
40
50
30
10
20
0012345
02735-004
6
Figure 6. Input Bias Current vs. Input Common-Mode Voltage at 5 V
150°C
125°C
INPUT COMMON-MODE VOLTAGE (V)
INPUT BIAS CURRENT (pA)
1500
500
1000
0
–1000
–500
–1500 012345
02735-005
6
V
S
= 5V
Figure 7. Input Bias Current vs. Input Common-Mode Voltage at 5 V
INPUT OFFSET VOLTAGE (µV)
NUMBER OF AMPLIFIERS
100
80
90
60
70
40
50
10
20
30
0
–2.5 –1.5 –0.5 0.5 1.5 2.5
02735-006
V
S
= 5V
V
CM
= 2.5V
T
A
= 25°C
Figure 8. Input Offset Voltage Distribution at 5 V
V
S
= 5V
T
A
= –40°C TO +125°C
TCVOS (nV/°C)
NUMBER OF AMPLIFIERS
7
6
5
4
3
2
1
002468
10
02735-007
Figure 9. Input Offset Voltage Drift
V
S
= 5V
T
A
= 25°C
SOURCE SINK
LOAD CURRENT (mA)
OUTPUT VOLTAGE (mV)
1k
100
10
1
0.1
0.01
0.0001 0.001 0.10.01 1 10
02735-008
Figure 10. Output Voltage to Supply Rail vs. Load Current at 5 V
AD8628/AD8629
Rev. C | Page 7 of 20
V
S
= 2.7V
SOURCE SINK
LOAD CURRENT (mA)
OUTPUT VOLTAGE (mV)
1k
100
10
1
0.1
0.01
0.0001 0.001 0.10.01 1 10
02735-009
Figure 11. Output Voltage to Supply Rail vs. Load Current at 2.7 V
VS = 5V
VCM = 2.5V
TA = –40°C TO +150°C
TEMPERATURE (°C)
INPUT BIAS CURRENT (pA)
1500
1150
900
450
100
0
–50 0 25–25 50 75 100 125 150 175
02735-010
Figure 12. Input Bias Current vs. Temperature
T
A
= 25°C
5V
2.7V
TEMPERATURE (
°C
)
SUPPLY CURRENT (µA)
1250
1000
750
500
250
0
–50 0 50 150100 200
02735-011
Figure 13. Supply Current vs. Temperature
T
A
= 25°C
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (
µ
A)
1000
800
600
400
200
0012 4536
02735-012
Figure 14. Supply Current vs. Supply Voltage
V
S
= 2.7V
C
L
= 20pF
R
L
= ∞
φ
M
= 52.1°
FREQUENCY (Hz)
OPEN-LOOP GAIN (dB)
70
60
50
40
30
20
0
–10
–20
10
–30
10k 100k 1M 10M
02735-013
45
90
135
180
225
0
PHASE SHIFT (Degrees)
Figure 15. Open-Loop Gain and Phase vs. Frequency
V
S
= 5V
C
L
= 20pF
R
L
= ∞
φ
M
= 52.1°
FREQUENCY (Hz)
OPEN-LOOP GAIN (dB)
70
60
50
40
30
20
0
–10
–20
10
–30
10k 100k 1M 10M
02735-014
45
90
135
180
225
0
PHASE SHIFT (Degrees)
Figure 16. Open-Loop Gain and Phase vs. Frequency
AD8628/AD8629
Rev. C | Page 8 of 20
FREQUENCY (Hz)
CLOSED-LOOP GAIN (dB)
70
60
50
40
30
20
0
–10
–20
10
–301k 10k 100k 1M 10M
02735-015
V
S
= 2.7V
C
L
= 20pF
R
L
= 2kΩ
A
V
= 100
A
V
= 10
A
V
= 1
Figure 17. Closed-Loop Gain vs. Frequency at 2.7 V
FREQUENCY (Hz)
CLOSED-LOOP GAIN (dB)
70
60
50
40
30
20
0
–10
–20
10
–301k 10k 100k 1M 10M
02735-016
V
S
= 5V
C
L
= 20pF
R
L
= 2kΩ
A
V
= 100
A
V
= 10
A
V
= 1
Figure 18. Closed-Loop Gain vs. Frequency at 5 V
FREQUENCY (Hz)
OUTPUT IMPEDANCE (
Ω
)
300
270
240
210
180
150
90
60
30
120
0
100 1k 10k 100k 1M 10M 100M
02735-017
V
S
= 2.7V
A
V
= 100
A
V
= 10
A
V
= 1
Figure 19. Output Impedance vs. Frequency at 2.7 V
FREQUENCY (Hz)
OUTPUT IMPEDANCE (
Ω
)
300
270
240
210
180
150
90
60
30
120
0
100 1k 10k 100k 1M 10M 100M
02735-018
V
S
= 5V
A
V
= 100
A
V
= 10
A
V
= 1
Figure 20. Output Impedance vs. Frequency at 5 V
V
S
= ±1.35V
C
L
= 300pF
R
L
= ∞
A
V
= 1
TIME (4µs/DIV)
VOLTAGE (500mV/DIV)
02735-019
Figure 21. Large Signal Transient Response at 2.7 V
V
S
= ±2.5V
C
L
= 300pF
R
L
= ∞
A
V
= 1
TIME (5µs/DIV)
VOLTAGE (1V/DIV)
02735-020
Figure 22. Large Signal Transient Response at 5 V
AD8628/AD8629
Rev. C | Page 9 of 20
V
S
= ±1.35V
C
L
= 50pF
R
L
= ∞
A
V
= 1
TIME (4µs/DIV)
VOLTAGE (50mV/DIV)
02735-021
Figure 23. Small Signal Transient Response at 2.7 V
V
S
= ±2.5V
C
L
= 50pF
R
L
= ∞
A
V
= 1
TIME (4µs/DIV)
VOLTAGE (50mV/DIV)
02735-022
Figure 24. Small Signal Transient Response at 5 V
CAPACITIVE LOAD (pF)
OVERSHOOT (%)
100
90
80
70
60
50
30
20
10
40
01 10 100 1k
02735-023
V
S
= ±1.35V
R
L
= 2kΩ
T
A
= 25°C
OS–
OS+
Figure 25. Small Signal Overshoot vs. Load Capacitance at 2.7 V
CAPACITIVE LOAD (pF)
OVERSHOOT (%)
80
70
60
50
30
20
10
40
01 10 100 1k
02735-024
V
S
= ±2.5V
R
L
= 2kΩ
T
A
= 25°C
OS–
OS+
Figure 26. Small Signal Overshoot vs. Load Capacitance at 5 V
TIME (2µs/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-025
V
S
= ±2.5V
A
V
= –50
R
L
= 10kΩ
C
L
= 0
CH1 = 50mV/DIV
CH2 = 1V/DIV
Figure 27. Positive Overvoltage Recovery
TIME (10µs/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-026
V
S
= ±2.5V
A
V
= –50
R
L
= 10kΩ
C
L
= 0
CH1 = 50mV/DIV
CH2 = 1V/DIV
Figure 28. Negative Overvoltage Recovery
AD8628/AD8629
Rev. C | Page 10 of 20
TIME (200µs/DIV)
VOLTAGE (1V/DIV)
02735-027
V
S
= ±2.5V
V
IN
= 1kHz @ ±3V p-p
C
L
= 0pF
R
L
= 10kΩ
A
V
= 1
Figure 29. No Phase Reversal
FREQUENCY (Hz)
CMRR (dB)
140
120
100
80
60
40
0
–20
–40
20
–60
100 1k 10k 100k 1M 10M
02735-028
V
S
= 2.7V
Figure 30. CMRR vs. Frequency at 2.7 V
FREQUENCY (Hz)
CMRR (dB)
140
120
100
80
60
40
0
–20
–40
20
–60
100 1k 10k 100k 1M 10M
02735-029
V
S
= 5V
Figure 31. CMRR vs. Frequency at 5 V
FREQUENCY (Hz)
PSRR (dB)
140
120
100
80
60
40
0
–20
–40
20
–60
100 1k 10k 100k 1M 10M
02735-030
V
S
= ±1.35V
+PSRR
–PSRR
Figure 32. PSRR vs. Frequency
FREQUENCY (Hz)
PSRR (dB)
140
120
100
80
60
40
0
–20
–40
20
–60
100 1k 10k 100k 1M 10M
02735-031
V
S
= ±2.5V
+PSRR
–PSRR
Figure 33. PSRR vs. Frequency
FREQUENCY (Hz)
OUTPUT SWING (V p-p)
3.0
2.5
2.0
1.5
1.0
0.5
0
100 1k 10k 100k 1M
02735-032
V
S
= 2.7V
R
L
= 10kΩ
T
A
= 25°C
A
V
= 1
Figure 34. Maximum Output Swing vs. Frequency
AD8628/AD8629
Rev. C | Page 11 of 20
FREQUENCY (Hz)
OUTPUT SWING (V p-p)
5.5
2.5
3.0
3.5
4.0
4.5
5.0
2.0
1.5
1.0
0.5
0
100 1k 10k 100k 1M
02735-033
V
S
= 5V
R
L
= 10kΩ
T
A
= 25°C
A
V
= 1
Figure 35. Maximum Output Swing vs. Frequency at 5 V
TIME (µs)
VOLTAGE (
µ
V)
0.60
0.45
0.30
0.15
–0.15
–0.30
–0.45
0
–0.60 012345678910
02735-034
V
S
= 2.7V
Figure 36. 0.1 Hz to 10 Hz Noise at 2.7 V
TIME (µs)
VOLTAGE (
µ
V)
0.60
0.45
0.30
0.15
–0.15
–0.30
–0.45
0
–0.60 012345678910
02735-035
V
S
= 5V
Figure 37. 0.1 Hz to 10 Hz Noise at 5 V
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/
√
Hz)
120
105
90
75
45
30
15
60
00 0.5 1.0 1.5 2.0 2.5
02735-036
V
S
= 2.7V
NOISE AT 1kHz = 21.3nV
Figure 38. Voltage Noise Density at 2.7 V from 0 Hz to 2.5 kHz
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/
√
Hz)
120
105
90
75
45
30
15
60
00 5 10 15 20 25
02735-037
V
S
= 2.7V
NOISE AT 10kHz = 42.4nV
Figure 39. Voltage Noise Density at 2.7 V from 0 Hz to 25 kHz
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/
√
Hz)
120
105
90
75
45
30
15
60
00 0.5 1.0 1.5 2.0 2.5
02735-038
V
S
= 5V
NOISE AT 1kHz = 22.1nV
Figure 40. Voltage Noise Density at 5 V from 0 Hz to 2.5 kHz
AD8628/AD8629
Rev. C | Page 12 of 20
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/
√
Hz)
120
105
90
75
45
30
15
60
00 5 10 15 20 25
02735-039
V
S
= 5V
NOISE AT 10kHz = 36.4nV
Figure 41. Voltage Noise Density at 5 V from 0 Hz to 25 kHz
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/
√
Hz)
120
105
90
75
45
30
15
60
005
02735-040
10
V
S
= 5V
Figure 42. Voltage Noise
VS = 2.7V TO 5V
TA = –40°C TO +125°C
TEMPERATURE (°C)
POWER SUPPLY REJECTION (dB)
150
130
120
140
110
100
90
60
70
80
50
–50 0 25–25 50 75 100 125
02735-041
Figure 43. Power Supply Rejection vs. Temperature
TEMPERATURE (
°
C)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
150
100
50
0
–50
–100
–50 25 50 750–25 100 125 150 175
02735-042
V
S
= 2.7V
T
A
= –40
°
C TO +150
°
C
I
SC
–
I
SC
+
Figure 44. Output Short-Circuit Current vs. Temperature
TEMPERATURE (
°
C)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
150
100
50
0
–50
–100
–50 25 50 750–25 100 125 150 175
02735-043
V
S
= 5V
T
A
= –40
°
C TO +150
°
C
I
SC
–
I
SC
+
Figure 45. Output Short-Circuit Current vs. Temperature
TEMPERATURE (
°
C)
OUTPUT-TO-RAIL VOLTAGE (mV)
1k
100
10
1
0.10
–50 25 50 750–25 100 125 150 175
02735-044
V
S
= 5V
V
CC
– V
OH
@ 1k
Ω
V
CC
– V
OH
@ 10k
Ω
V
CC
– V
OH
@ 100k
Ω
V
OL
– V
EE
@ 1k
Ω
V
OL
– V
EE
@ 10k
Ω
V
OL
– V
EE
@ 100k
Ω
Figure 46. Output-to-Rail Voltage vs. Temperature
AD8628/AD8629
Rev. C | Page 13 of 20
TEMPERATURE (
°
C)
OUTPUT-TO-RAIL VOLTAGE (mV)
1k
100
10
1
0.10
–50 25 50 750–25 100 125 150 175
02735-045
V
S
= 2.7V
V
CC
– V
OH
@ 1k
Ω
V
CC
– V
OH
@ 10k
Ω
V
CC
– V
OH
@ 100k
Ω
V
OL
– V
EE
@ 1k
Ω
V
OL
– V
EE
@ 10k
Ω
V
OL
– V
EE
@ 100k
Ω
Figure 47. Output-to-Rail Voltage vs. Temperature
FREQUENCY (Hz)
CHANNEL SEPARATION (dB)
140
120
100
80
60
40
20
01k 10k 100k 1M 10M
02735-062
VOUT
VIN
28mV p-p
–2.5V
+2.5V R1
10kΩ
V–
V+
–
+
V+
V–
AB
R2
100Ω
VSY = ±2.5V
Figure 48. AD8629 Channel Separation
AD8628/AD8629
Rev. C | Page 14 of 20
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.
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%.
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 ping-
pong 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.
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.
1/F NOISE
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.
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.
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.
MK AT 1kHz FOR ALL 3 GRAPHS
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/
√
Hz)
120
105
90
75
60
45
30
15
0042861
02735-046
012
LTC2050
(89.7nV/√Hz)
LMC2001
(31.1nV/√Hz)
AD8628
(19.4nV/√Hz)
Figure 49. Noise Spectral Density of AD8628 vs. Competition
AD8628/AD8629
Rev. C | Page 15 of 20
PEAK-TO-PEAK NOISE
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.
e
n
p-p = 0.5µV
BW = 0.1Hz TO 10Hz
TIME (1s/DIV)
VOLTAGE (0.5µV/DIV)
02735-047
Figure 50. AD8628 Peak-to-Peak Noise
e
n
p-p = 2.3µV
BW = 0.1Hz TO 10Hz
TIME (1s/DIV)
VOLTAGE (0.5µV/DIV)
02735-048
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.
470pF
OUT
100kΩ
IN
1kΩ
02735-049
Figure 52. Test Circuit: First-Order Low-Pass Filter—×101 Gain
and 3 kHz Corner Frequency
FREQUENCY (Hz)
NOISE (dB)
50
45
40
35
30
25
15
10
5
20
00 30 60 10090807050402010
02735-050
Figure 53. Simulation Transfer Function of the Test Circuit
FREQUENCY (kHz)
NOISE (dB)
50
45
40
35
30
25
15
10
5
20
00 30 60 10090807050402010
02735-051
Figure 54. Actual Transfer Function of Test Circuit
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
For a first-order filter, the total integrated noise from the
AD8628 is lower than the LTC2050.
3dB FILTER BANDWIDTH (Hz)
RMS NOISE (
µ
V)
10
1
0.110 100 10k1k
02735-052
LTC2050
AD8551 AD8628
Figure 55. 3 dB Filter Bandwidth in Hz
AD8628/AD8629
Rev. C | Page 16 of 20
INPUT OVERVOLTAGE PROTECTION
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.
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.
OUTPUT PHASE REVERSAL
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.
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.
OVERLOAD RECOVERY TIME
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.
TIME (500
µ
s/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-053
CH1 = 50mV/DIV
CH2 = 1V/DIV
A
V
= –50
Figure 56. Positive Input Overload Recovery for the AD8628
TIME (500
µ
s/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-054
CH1 = 50mV/DIV
CH2 = 1V/DIV
A
V
= –50
Figure 57. Positive Input Overload Recovery for LTC2050
TIME (500
µ
s/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-055
CH1 = 50mV/DIV
CH2 = 1V/DIV
A
V
= –50
Figure 58. Positive Input Overload Recovery for LMC2001
AD8628/AD8629
Rev. C | Page 17 of 20
TIME (500
µ
s/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-056
CH1 = 50mV/DIV
CH2 = 1V/DIV
A
V
= –50
Figure 59. Negative Input Overload Recovery for the AD8628
TIME (500
µ
s/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-057
CH1 = 50mV/DIV
CH2 = 1V/DIV
A
V
= –50
Figure 60. Negative Input Overload Recovery for LTC2050
TIME (500
µ
s/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-058
CH1 = 50mV/DIV
CH2 = 1V/DIV
A
V
= –50
Figure 61. Negative Input Overload Recovery for LMC2001
The results shown in Figure 56 to Figure 61 are summarized in
Table 5.
Table 5. Overload Recovery Time
Product
Positive Overload
Recovery (µs)
Negative Overload
Recovery (µs)
AD8628 6 9
LTC2050 650 25,000
LMC2001 40,000 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.
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 elimi-
nates 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.
5V
100k
Ω
10kΩ
5V
100µV – 300µV
100Ω
TO BIAS
VOLTAGE
10kΩ
f
C
≈1.6Hz
IR
DETECTOR
100kΩ
10µF
1/2 AD8629
1/2 AD8629
02735-059
Figure 62. AD8629 Used as Preamplifier for Thermopile
AD8628/AD8629
Rev. C | Page 18 of 20
PRECISION CURRENT SHUNTS
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.
R
S
0.1Ω
SUPPLY IR
L
100Ω100kΩ
C
5V
100Ω100kΩ
C
e = 1,000 R
S
I
100mV/mA
AD8628
02735-060
Figure 63. Low-Side Current Sensing
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.
OUTPUT AMPLIFIER FOR HIGH PRECISION DACs
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).
Rail-to-rail input and output provide full-scale output with very
little error. Output impedance of the DAC is constant and code-
independent, 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:
()
(
)
()
22 8628ADtDACtTOTALt SSS +=
03023-061
AD5541/AD5542
AD8628
DGND
*AD5542 ONLY
V
DD
REF(REF*) REFS*
OUT
SCLK
DIN
CS
AGND
5V 2.5V
UNIPOLAR
OUTPUT
LDAC*
0.1
µ
F
10
µ
F
0.1
µ
F
SERIAL
INTERFACE
Figure 64. AD8628 Used as an Output Amplifier
AD8628/AD8629
Rev. C | Page 19 of 20
OUTLINE DIMENSIONS
PIN 1
1.60 BSC 2.80 BSC
1.90
BSC
0.95 BSC
13
45
2
0.20
0.08
0.60
0.45
0.30
8°
4°
0.50
0.30
0.10 MAX SEATING
PLANE
1.00 MAX
0.90
0.87
0.84
COMPLIANT TO JEDEC STANDARDS MO-193AB
2.90 BSC
Figure 65. 5-Lead Thin Small Outline Transistor Package [TSOT]
(UJ-5)
Dimensions shown in millimeters
PIN 1
1.60 BSC 2.80 BSC
1.90
BSC
0.95 BSC
1
3
4 5
2
0.22
0.08 10°
5°
0°
0.50
0.30
0.15 MAX SEATING
PLANE
1.45 MAX
1.30
1.15
0.90
2.90 BSC
0.60
0.45
0.30
COMPLIANT TO JEDEC STANDARDS MO-178AA
Figure 66. 5-Lead Small Outline Transistor Package [SOT-23]
(RT-5)
Dimensions shown in millimeters
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)
41
85
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2440)
5.80 (0.2284)
0.51 (0.0201)
0.31 (0.0122)
COPLANARIT
Y
0.10
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-012AA
Figure 67. 8-Lead Standard Small Outline Package [SOIC]
Narrow Body (R-8)
Dimensions shown in millimeters and (inches)
0.80
0.60
0.40
8°
0°
4
85
4.90
BSC
PIN 1 0.65 BSC
3.00
BSC
SEATING
PLANE
0.15
0.00
0.38
0.22
1.10 MAX
3.00
BSC
COPLANARITY
0.10
0.23
0.08
COMPLIANT TO JEDEC STANDARDS MO-187AA
Figure 65. 8-Lead Standard Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
AD8628/AD8629
Rev. C | Page 20 of 20
ORDERING GUIDE
Model Temperature Range Package Description Package Option Branding
AD8628AUJ-R2 −40°C to +125°C 5-Lead TSOT-23 UJ-5 AYB
AD8628AUJ-REEL −40°C to +125°C 5-Lead TSOT-23 UJ-5 AYB
AD8628AUJ-REEL7 −40°C to +125°C 5-Lead TSOT-23 UJ-5 AYB
AD8628AUJZ-R21−40°C to +125°C 5-Lead TSOT-23 UJ-5 AYB
AD8628AUJZ-REEL1 −40°C to +125°C 5-Lead TSOT-23 UJ-5 AYB
AD8628AUJZ-REEL71 −40°C to +125°C 5-Lead TSOT-23 UJ-5 AYB
AD8628AR −40°C to +125°C 8-Lead SOIC R-8
AD8628AR-REEL −40°C to +125°C 8-Lead SOIC R-8
AD8628AR-REEL7 −40°C to +125°C 8-Lead SOIC R-8
AD8628ARZ1 −40°C to +125°C 8-Lead SOIC R-8
AD8628ARZ-REEL1 −40°C to +125°C 8-Lead SOIC R-8
AD8628ARZ-REEL71 −40°C to +125°C 8-Lead SOIC R-8
AD8628ART-R2 −40°C to +125°C 5-Lead SOT-23 RT-5 AYA
AD8628ART-REEL7 −40°C to +125°C 5-Lead SOT-23 RT-5 AYA
AD8628ARTZ-R21 −40°C to +125°C 5-Lead SOT-23 RT-5 AYA
AD8628ARTZ-REEL71 −40°C to +125°C 5-Lead SOT-23 RT-5 AYA
AD8629ARZ1 −40°C to +125°C 8-Lead SOIC R-8
AD8629ARZ-REEL1 −40°C to +125°C 8-Lead SOIC R-8
AD8629ARZ-REEL71 −40°C to +125°C 8-Lead SOIC R-8
AD8629ARMZ-R21 −40°C to +125°C 8-Lead MSOP RM-8 A06
AD8629ARMZ-REEL1 −40°C to +125°C 8-Lead MSOP RM-8 A06
1 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)
