Datasheet AD8638 Datasheet (ANALOG DEVICES)

16 V Auto-Zero, Rail-to-Rail Output

O

FEATURES

Low offset voltage: 9 μV maximum
Offset drift: 0.04 μV/°C maximum
Rail-to-rail output swing
5 V to 16 V single-supply or ±2.5 V to ±8 V dual-supply

operation
High gain: 136 dB typical
High CMRR: 133 dB typical
High PSRR: 143 dB typical
Very low input bias current: 40 pA maximum
Low supply current: 1.3 mA maximum
AD8639: qualified for automotive applications

APPLICATIONS

Pressure and position sensors
Strain gage amplifiers
Medical instrumentation
Thermocouple amplifiers
Automotive sensors
Precision references
Precision current sensing

GENERAL DESCRIPTION

The AD8638/AD8639 are single and dual wide bandwidth,
auto-zero amplifiers featuring rail-to-rail output swing and low
noise. These amplifiers have very low offset, drift, and bias
current. Operation is fully specified from 5 V to 16 V single
supply (±2.5 V to ±8 V dual supply).

The AD8638/AD8639 provide benefits previously found only
in expensive zero-drift or chopper-stabilized amplifiers. Using
the Analog Devices, Inc., topology, these auto-zero amplifiers
combine low cost with high accuracy and low noise. No exter­nal capacitors are required. In addition, the AD8638/AD8639
greatly reduce the digital switching noise found in most chopper­stabilized amplifiers.

With a typical offset voltage of only 3 μV, drift of 0.01 μV/°C,
and noise of 1.2 μV p-p (0.1 Hz to 10 Hz), the AD8638/AD8639
are 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 ranges. Many systems can take
advantage of the rail-to-rail output swing provided by the
AD8638/AD8639 to maximize signal-to-noise ratio (SNR).

Operational Amplifiers

AD8638/AD8639

PIN CONFIGURATIONS

UT

1

AD8638

TOP VIEW

V–

2

(Not to S cale)

+IN

3

Figure 1. 5-Lead SOT-23 (RJ-5)

NC

1

AD8638

–IN

2

+IN

3

TOP VIEW

(Not to Scale)

4

V–

NC = NO CONNECT

Figure 2. 8-Lead SOIC_N (R-8)

OUT A

1

AD8639

2

–IN A
+IN A

V–

TOP VIEW

3

(Not to Scale)

4

Figure 3. 8-Lead MSOP (RM-8)

8-Lead SOIC_N (R-8)

PIN 1

1OUT A

INDICATOR

2–IN A

AD8639

3+IN A

TOP VIEW

(Not to S cal e)

4v–

NOTES

1. PIN 4AND THE EXPOSED PAD
MUST BE CONNECTEDTO V–.

Figure 4. 8-Lead LFCSP_WD (CP-8-5)

The AD8638/AD8639 are specified for the extended industrial
temperature range (−40°C to +125°C). The single AD8638 is
available in tiny 5-lead SOT-23 and 8-lead SOIC packages.
The dual AD8639 is available in 8-lead MSOP, 8-lead SOIC, and
8-lead LFCSP packages. See the Ordering Guide for automotive
grades.

The AD8638/AD8639 are members of a growing series of auto­zero op amps offered by Analog Devices (see Ta b l e 1 ).

Table 1. Auto-Zero Op Amps

Supply 2.7 V to 5 V 2.7 V to 5 V Low Power 5 V to 16 V

Single AD8628 AD8538 AD8638
Dual AD8629 AD8539 AD8639
Quad AD8630

V+

5

–IN

4

NC

8

V+

7

OUT

6
5

NC

V+

8
7

OUT B

6

–IN B
+IN B

5

8V+
7OUT B
6 –IN B
5 +IN B

06895-001

06895-002

06895-203

06895-204

Rev. F

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: [phone] www.analog.com
Fax: [phone] ©2007–2010 Analog Devices, Inc. All rights reserved.

AD8638/AD8639

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

General Description ......................................................................... 1

Pin Configurations ........................................................................... 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

Electrical Characteristics—5 V Operation................................ 3

Electrical Characteristics—16 V Operation ............................. 4

Absolute Maximum Ratings ............................................................ 5

Thermal Resistance ...................................................................... 5

ESD Caution .................................................................................. 5

Typical Performance Characteristics ............................................. 6

REVISION HISTORY

6/10—Rev. E to Rev. F

Changes to Features Section and General Description Section . 1

Updated Outline Dimensions ....................................................... 16

Changes to Ordering Guide .......................................................... 18

Added Automotive Products Section .......................................... 18

6/09—Rev. D to Rev. E

Changes to Figure 4 .......................................................................... 1

Changes to Endnote 1 and Endnote 2, Table 4 ............................. 5

Changes to Input Voltage Range Section .................................... 14

Updated Outline Dimensions ....................................................... 16

Changes to Ordering Guide .......................................................... 18

12/08—Rev. C to Rev. D

Changes to Endnote 1, Table 4 ........................................................ 5

Changes to Ordering Guide .......................................................... 28

5/08—Rev. B to Rev. C

Added LFCSP_WD Package ............................................. Universal

Inserted Figure 4; Renumbered Sequentially ................................ 1

Changes to Layout ............................................................................ 1

Changes to General Description .................................................... 1

Changes to Offset Voltage Drift for All Packages Except SOT-23

Parameter in Table 2 ......................................................................... 3

Changes to Table 5 ............................................................................ 5

Updated Outline Dimensions ....................................................... 16

Changes to Ordering Guide .......................................................... 17

Theory of Operation ...................................................................... 14

1/f Noise ....................................................................................... 14

Input Voltage Range ................................................................... 14

Output Phase Reversal ............................................................... 14

Overload Recovery Time .......................................................... 14

Infrared Sensors .......................................................................... 15

Precision Current Shunt Sensor ............................................... 15

Output Amplifier for High Precision DACs ........................... 15

Outline Dimensions ....................................................................... 16

Ordering Guide .......................................................................... 18

Automotive Products ................................................................. 18

4/08—Rev. A to Rev. B

Added AD8639 ................................................................... Universal

Added 8-lead MSOP Package ........................................... Universal

Changes to Features .......................................................................... 1

Changes to General Description ..................................................... 1

Changes Table 2 ................................................................................. 3

Changes to Table 3 ............................................................................. 4

Changes to Table 4, Added Endnote 1 and Endnote 2 ................. 5

Changes to Figure 4 through Figure 9 ............................................ 6

Changes to Figure 11, Figure 12, Figure 14, and Figure 15.......... 7

Changes to Figure 16 through Figure 27 ........................................ 8

Changes to Figure 28 through Figure 33 ..................................... 10

Changes to Figure 34 through Figure 39 ..................................... 11

Changes to Figure 41 and Figure 44............................................. 12

Inserted Figure 46, Figure 47, Figure 49, and Figure 50;

Renumbered Sequentially ............................................................. 13

Changes to Figure 51, Figure 52, and Figure 53 ......................... 15

Updated Outline Dimensions ....................................................... 16

Changes to Ordering Guide .......................................................... 17

11/07—Rev. 0 to Rev. A

Change to Large Signal Voltage Gain Specification ...................... 4

11/07—Revision 0: Initial Version

Rev. F | Page 2 of 20

AD8638/AD8639

SPECIFICATIONS

ELECTRICAL CHARACTERISTICS—5 V OPERATION

VSY = 5 V, VCM = VSY/2, TA = 25°C, unless otherwise noted.

Table 2.

Parameter Symbol Conditions Min Typ Max Unit

INPUT CHARACTERISTICS

Offset Voltage VOS 3 9 μV

−40°C ≤ TA ≤ +125°C 23 μV

−0.1 V ≤ VCM ≤ +3.0 V 3 9 μV

−40°C ≤ TA ≤ +125°C 23 μV

Input Bias Current IB 1.5 40 pA

−40°C ≤ TA ≤ +85°C 7 40 pA

−40°C ≤ TA ≤ +125°C 45 105 pA

Input Offset Current IOS 7 40 pA

−40°C ≤ TA ≤ +85°C 7 40 pA

−40°C ≤ TA ≤ +125°C 16.5 60 pA

Input Voltage Range −40°C ≤ TA ≤ +125°C −0.1 +3 V

Common-Mode Rejection Ratio CMRR VCM = 0 V to 3 V 118 133 dB

−40°C ≤ TA ≤ +125°C 118 dB

Large Signal Voltage Gain AVO R

−40°C ≤ TA ≤ +125°C 119 dB
∆V

Offset Voltage Drift for All Packages

/∆T −40°C ≤ TA ≤ +125°C 0.01 0.06 μV/°C

OS

Except SOT-23
Offset Voltage Drift for SOT-23 ∆VOS/∆T −40°C ≤ TA ≤ +125°C 0.04 0.15 μV/°C
Input Resistance RIN 22.5 TΩ
Input Capacitance, Differential Mode C
Input Capacitance, Common Mode C

4 pF

INDM

1.7 pF

INCM

OUTPUT CHARACTERISTICS

Output Voltage High VOH R

−40°C ≤ TA ≤ +125°C 4.97 V
R

−40°C ≤ TA ≤ +125°C 4.86 V
Output Voltage Low VOL R

−40°C ≤ TA ≤ +125°C 15 mV
R

−40°C ≤ TA ≤ +125°C 55 mV
Short-Circuit Current ISC T
Closed-Loop Output Impedance Z

f = 100 kHz, AV = 1 4.2 Ω

OUT

POWER SUPPLY

Power Supply Rejection Ratio PSRR VSY = 4.5 V to 16 V 127 143 dB

−40°C ≤ TA ≤ +125°C 125 dB
Supply Current per Amplifier ISY I

−40°C ≤ TA ≤ +125°C 1.5 mA

DYNAMIC PERFORMANCE

Slew Rate SR RL = 10 kΩ, CL = 20 pF, AV = 1 2.5 V/μs
Settling Time to 0.1% tS V
Overload Recovery Time 50 μs
Gain Bandwidth Product GBP RL = 2 kΩ, CL = 20 pF, AV = 1 1.35 MHz
Phase Margin ΦM R

NOISE PERFORMANCE

Voltage Noise en p-p 0.1 Hz to 10 Hz 1.2 μV p-p
Voltage Noise Density en f = 1 kHz 60 nV/√Hz

= 10 kΩ, VO = 0.5 V to 4.5 V 120 136 dB

L

= 10 kΩ to VCM 4.97 4.985 V

L

= 2 kΩ to VCM 4.90 4.93 V

L

= 10 kΩ to VCM 7.5 10 mV

L

= 2 kΩ to VCM 32 40 mV

L

= 25°C ±19 mA

A

= 0 mA 1.0 1.3 mA

O

= 2 V step, CL = 20 pF, RL = 1 kΩ, AV = 1 3 μs

IN

= 2 kΩ, CL = 20 pF, AV = 1 70 Degrees

L

Rev. F | Page 3 of 20

AD8638/AD8639

ELECTRICAL CHARACTERISTICS—16 V OPERATION

VSY = 16 V, VCM = VSY/2, TA = 25°C, unless otherwise noted.

Table 3.

Parameter Symbol Conditions Min Typ Max Unit

INPUT CHARACTERISTICS

Offset Voltage VOS 3 9 μV

−40°C ≤ TA ≤ +125°C 23 μV

Input Bias Current IB 1 75 pA

Input Offset Current IOS 20 70 pA

Input Voltage Range −40°C ≤ TA ≤ +125°C −0.1 +14 V
Common-Mode Rejection Ratio CMRR VCM = 0 V to 14 V 127 142 dB

−40°C ≤ TA ≤ +125°C 127 dB
Large Signal Voltage Gain AVO R

−40°C ≤ TA ≤ +125°C 130 dB
Offset Voltage Drift for All Packages

∆V

OS

Except SOT-23
Offset Voltage Drift for SOT-23 ∆VOS/∆T −40°C ≤ TA ≤ +125°C 0.04 0.15 μV/°C
Input Resistance RIN 22.5 TΩ
Input Capacitance, Differential Mode C
Input Capacitance, Common Mode C

INDM

INCM

OUTPUT CHARACTERISTICS

Output Voltage High VOH R

−40°C ≤ TA ≤ +125°C 15.93 V
R

−40°C ≤ TA ≤ +125°C 15.70 V
Output Voltage Low VOL R

−40°C ≤ TA ≤ +125°C 60 mV
R

−40°C ≤ TA ≤ +125°C 200 mV
Short-Circuit Current ISC T
Closed-Loop Output Impedance Z

OUT

POWER SUPPLY

Power Supply Rejection Ratio PSRR VSY = 4.5 V to 16 V 127 143 dB

−40°C ≤ TA ≤ +125°C 125 dB
Supply Current per Amplifier ISY I

−40°C ≤ TA ≤ +125°C 1.7 mA
DYNAMIC PERFORMANCE

Slew Rate SR RL = 10 kΩ, CL = 20 pF, AV = 1 2 V/μs
Settling Time to 0.1% tS V
Overload Recovery Time 50 μs
Gain Bandwidth Product GBP RL = 2 kΩ, CL = 20 pF, AV = 1 1.5 MHz
Phase Margin ΦM R

NOISE PERFORMANCE

Voltage Noise en p-p 0.1 Hz to 10 Hz 1.2 μV p-p
Voltage Noise Density en f = 1 kHz 60 nV/√Hz

−0.1 V ≤ VCM ≤ +14 V

−40°C ≤ TA ≤ +125°C

−40°C ≤ TA ≤ +85°C

−40°C ≤ TA ≤ +125°C

−40°C ≤ TA ≤ +85°C

−40°C ≤ T

= 10 kΩ, VO = 0.5 V to 15.5 V 130 147 dB

L

≤ +125°C

A

3 9 μV
23 μV

4 75 pA
85 250 pA

20 75 pA
50 150 pA

/∆T −40°C ≤ TA ≤ +125°C 0.03 0.06 μV/°C

4 pF

1.7 pF

= 10 kΩ to VCM 15.94 15.96 V

L

= 2 kΩ to VCM 15.77 15.82 V

L

= 10 kΩ to VCM 30 40 mV

L

= 2 kΩ to VCM 120 140 mV

L

= 25°C ±37 mA

A

f = 100 kHz, AV = 1 3.0 Ω

= 0 mA 1.25 1.5 mA

O

= 4 V step, CL = 20 pF, RL = 1 kΩ, AV = 1 4 μs

IN

= 2 kΩ, CL = 20 pF, AV = 1 74 Degrees

L

Rev. F | Page 4 of 20

AD8638/AD8639

ABSOLUTE MAXIMUM RATINGS

Table 4.

Parameter Rating

Supply Voltage 16 V

Input Voltage GND − 0.3 V to V

+ 0.3 V

SY+

Input Current1 ±10 mA

Differential Input Voltage2 ±VSY

Output Short-Circuit Duration to GND Indefinite

Storage Temperature Range −65°C to +150°C

Operating Temperature Range −40°C to +125°C

Junction Temperature Range −65°C to +150°C

Lead Temperature (Soldering, 60 sec) 300°C

1

Input pins have clamp diodes to the supply pins. Input current should be

limited to 10 mA or less whenever input signals exceed either power supply
rail by 0.3 V.

2

Inputs are protected against high differential voltages by internal 1 kΩ series

resistors and back-to-back diode-connected N-MOSFETs (with a typical VT of

1.25 V for VCM of 0 V).

Stresses above those listed under Absolute Maximum Ratings

may cause permanent damage to the device. This is a stress

rating only; functional operation of the device at these or any

other conditions above those indicated in the operational

section of this specification is not implied. Exposure to absolute

maximum rating conditions for extended periods may affect

device reliability.

THERMAL RESISTANCE

Table 5. Thermal Resistance

Package Type θ

5-Lead SOT-23 (RJ-5) 230 146 °C/W
8-Lead SOIC_N (R-8) 158 43 °C/W
8-Lead MSOP (RM-8) 206 44 °C/W
8-Lead LFCSP_WD (CP-8-5)2 75 18 °C/W

1

θJA is specified for the worst-case conditions, that is, a device soldered in a

circuit board for surface-mount packages. This was measured using a
standard two-layer board.

2

Exposed pad is soldered to t

he application board.

1

θ

JA

JC

Unit

ESD CAUTION

Rev. F | Page 5 of 20

AD8638/AD8639

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C, unless otherwise noted.

1400

1200

VSY = 5V
0V  V

CM

 +3V

6000

5000

VSY = 16V
0V  V

CM

 +14V

1000

800

600

400

NUMBER OF AMPL IFIERS

200

0

–10 10

–5 50

VOS (µV)

06895-003

Figure 5. Input Offset Voltage Distribution

NUMBER OF AMPLIFIERS

25

20

15

10

5

VSY = ±2.5V
–40°C  T
SOIC PACKAGE

 +125°C

A

4000

3000

2000

NUMBER OF AMPLIFIERS

1000

0

–10 –5 0 5 10

VOS (µV)

06895-006

Figure 8. Input Offset Voltage Distribution

12

10

8

6

4

NUMBER OF AMPLIFIERS

2

VSY = ±8V
–40°C  T
SOIC PACKAGE

 +125°C

A

0

0

4 8 12 16 20 24 28 32 36 40

TCVOS (nV/°C)

06895-004

Figure 6. Input Offset Voltage Drift Distribution

10.0
VSY = 5V

–0.5V  V

7.5

5.0

2.5

(µV)

0

OS

V

–2.5

–5.0

–7.5

–10.0

–0.5 4

 +3.9V

CM

0 0.5 1 1.5 2.0 2.5 3.0 3.5

VCM (V)

06895-005

Figure 7. Input Offset Voltage vs. Common-Mode Voltage

0

0 4 8 1216202428323640

TCVOS (nV/°C)

Figure 9. Input Offset Voltage Drift Distribution

10.0

7.5

5.0

2.5

(µV)

0

OS

V

–2.5

–5.0

–7.5

–10.0

–0.5

VCM (V)

VSY = 16V
–0.5V  V

Figure 10. Input Offset Voltage vs. Common-Mode Voltage

 +14.5V

CM

06895-007

14.513.011.510.08.57.05.54.02.51.0

06895-008

Rev. F | Page 6 of 20

AD8638/AD8639

TA = 25°C, unless otherwise noted.

100

VSY = ±2.5V

10

100

10

VSY = ±8V

(pA)

B

I

1

0.1
25 1251007550

TEMPERATURE (°C)

06895-117

Figure 11. Input Bias Current vs. Temperature

10k

VSY = ±2.5V

1k

100

10

1

OUTPUT VOLTAGE TO SUPPLY RAIL (mV)

0.1

0.001 0.10.01 1 10010

VDD – V

OH

LOAD CURRENT (mA)

VOL – V

SS

6895-009

Figure 12. Output Voltage to Supply Rail vs. Load Current

120

VSY = 5V

= 2k

R

L

100

VDD – V

OH

1

(pA)

B

I

0.1

0.01
25 1251007550

TEMPERATURE (°C)

Figure 14. Input Bias Current vs. Temperature

10k

VSY = ±8V

1k

VDD – V

OH

100

10

OUTPUT VOLTAGE TO SUPPLY RAIL (mV)

1

0.001 0.10.01 1 10010
LOAD CURRENT (mA)

VOL – V

Figure 15. Output Voltage to Supply Rail vs. Load Current

250

VSY = 16V

= 2k

R

L

200

06895-118

SS

6895-012

80

60

40

20

OUTPUT VO LTAGE TO SUPPLY RAI L (mV)

0

–40 0 25–25 50 75 100 125

TEMPERATURE (°C)

V

OL

Figure 13. Output Voltage to Supply Rail vs. Temperature

6895-010

Rev. F | Page 7 of 20

VDD– V

150

100

50

OUTPUT VO LTAGE TO SUPPLY RAIL (mV)

0

–40 0 25–25 50 75 100 125

TEMPERATURE (°C)

OH

V

OL

Figure 16. Output Voltage to Supply Rail vs. Temperature

6895-013

AD8638/AD8639

TA = 25°C, unless otherwise noted.

120
100

80
60
40
20

–20

GAIN (dB)

–40
–60

–80
–100
–120

GAIN

0

VSY = ±2.5V

= 2k

R

L

1k 10k 100k 1M 10M

PHASE

CL = 20pF

CL = 200pF

FREQUENCY (Hz)

Figure 17. Open-Loop Gain and Phase vs. Frequency

60

AV = +100

40

VSY = ±2.5V
R

L

C

L

= 2k
= 20pF

120
100
80
60
40
20
0
–20
–40
–60
–80
–100
–120

120
100

80
60
40
20

–20

GAIN (dB)

PHASE (Degrees)

06895-016

–40
–60

–80
–100
–120

GAIN

00

VSY = ±8V

= 2k

R

L

1k 10k 100k 1M 10M

PHASE

CL = 20pF

CL = 200pF

FREQUENCY (Hz)

120
100
80
60
40
20

–20
–40
–60
–80
–100
–120

PHASE (Degrees)

06895-017

Figure 20. Open-Loop Gain and Phase vs. Frequency

60

40

AV = +100

VSY = ±8V
R

= 2k

L

C

= 20pF

L

AV = +10

20

AV = +1

0

CLOSED-LOOP GAIN (dB)

–20

–40

1k 10M

10k 100k 1M

FREQUENCY (Hz)

Figure 18. Closed-Loop Gain vs. Frequency

1k

VSY = ±2.5V

100

A

= –10

V

()

10

OUT

Z

1

0.1

AV = –100

= +1

A

V

100 1k 10M

10k 100k 1M

FREQUENCY (Hz)

Figure 19. Output Impedance vs. Frequency

AV = +10

20

AV = +1

0

CLOSED-LOOP GAIN (dB)

–20

–40

6895-018

1k 10M

10k 100k 1M

FREQUENCY (Hz)

06895-019

Figure 21. Closed-Loop Gain vs. Frequency

1k

VSY = ±8V

100

AV = –10

()

10

OUT

Z

0.1

06895-100

AV = –100

1

100 10M1M100k10k1k

FREQUENCY (Hz)

AV = +1

06895-119

Figure 22. Output Impedance vs. Frequency

Rev. F | Page 8 of 20

AD8638/AD8639

TA = 25°C, unless otherwise noted.

140

VSY = ±2.5V

120

140

VSY = ±8V

120

100

80

60

CMRR (dB)

40

20

0

100 1k 10k 100k 1M 10M

FREQUENCY (Hz)

06895-113

Figure 23. CMRR vs. Frequency

120

100

80

60

40

PSRR (dB)

20

PSRR–

VSY = ±2.5V

PSRR+

100

80

60

CMRR (dB)

40

20

0

100 10M1M100k10k1k

FREQUENCY (Hz)

06895-120

Figure 26. CMRR vs. Frequency

120

100

80

60

40

PSRR (dB)

20

PSRR–

PSRR+

VSY = ±8V

0

–20

10 100 1k 10k 100k 1M 10M

FREQUENCY (Hz)

06895-111

Figure 24. PSRR vs. Frequency

80

= ±2.5V

V

SY

R

= 10k

L

70

60

50

40

30

OVERSHOOT (%)

20

10

0

10

LOAD CAPACITANCE (pF)

100 1k

OS+
OS–

06895-126

Figure 25. Small Signal Overshoot vs. Load Capacitance

0

–20

10 100 1k 10k 100k 1M 10M

FREQUENCY (Hz)

Figure 27. PSRR vs. Frequency

80

VSY = ±8V
R

= 10k

L

70

60

50

40

30

OVERSHOOT (%)

20

10

0

10

LOAD CAPACITANCE (pF)

100 1k

Figure 28. Small Signal Overshoot vs. Load Capacitance

06895-112

OS+
OS–

06895-127

Rev. F | Page 9 of 20

AD8638/AD8639

TA = 25°C, unless otherwise noted.

VSY = ±2.5V
A

= +1

V

C

= 200pF

L

R

= 10k

L

VOLTAGE (500mV/DI V )

TIME (2µs/DIV)

06895-101

Figure 29. Large Signal Transient Response

VSY = ±2.5V
A

= +1

V

C

= 200pF

L

R

= 10k

L

VOLTAGE (50mV/DIV)

VSY = ±8V
A

= +1

V

C

= 200pF

L

R

= 10k

L

VOLTAGE (2V/DIV)

TIME (2µs/DIV)

Figure 32. Large Signal Transient Response

VSY = ±8V
A

= +1

V

C

= 200pF

L

R

= 10k

L

VOLTAGE (50mV/DIV)

06895-102

TIME (2µs/DIV)

Figure 30. Small Signal Transient Response

0.05

0

–0.05

–0.10

–0.15

INPUT VOLTAGE (50mV/DIV)

TIME (10µs/DIV)

Figure 31. Negative Overload Recovery

INPUT VOLTAGE

= ±2.5V

V

SY

A

= –100

V

OUTPUT VOLTAGE

06895-103

Figure 33. Small Signal Transient Response

0.05

0

–0.05

–0.10

3

2

1

OUTPUT VOLTAGE (1V/DIV)

0

06895-132

–1

–0.15

INPUT VOLTAGE (50mV/DIV)

Figure 34. Negative Overload Recovery

TIME (2µs/DIV)

INPUT VOLTAGE

VSY = ±8V
A

OUTPUT VOLTAGE

TIME (10µ s /DIV)

= –100

V

06895-104

10

5

OUTPUT VOLTAGE (5V/DIV)

0

06895-133

–5

Rev. F | Page 10 of 20

AD8638/AD8639

V

V

V

V

TA = 25°C, unless otherwise noted.

0.15

0.10

0.05

V

= ±2.5V

SY

= –100

A

V

0

INPUT VOLTAGE

0.15

0.10

0.05

= ±8V

V

SY

= –100

A

V

0

INPUT VOLTAGE

–0.05

OUT PU T VOLTA G E

INPUT VOLTAGE (50mV/DIV)

TIME (1 0µ s/DIV)

1

0

–1

OUTPUT VOLTAGE (1V/DIV)

–2

06895-134

–3

Figure 35. Positive Overload Recovery

INPUT

1V/DI

ERROR BAND

OUTPUT

VSY = ±2.5V

TIME (4µs/DIV)

+2mV

0

–2mV

06895-136

Figure 36. Positive Settling Time to 0.1%

–0.05

OUTPUT VOLTAGE

INPUT VOLTAGE (50mV/DIV)

TIME (10µs/DIV)

5

0

–5

–10

–15

OUTPUT VOLTAGE (5V/DIV)

06895-135

Figure 38. Positive Overload Recovery

INPUT

2V/DI

ERROR BAND

TIME (4µs/DIV)

OUTPUT

V

= ±8V

SY

+2mV
0

–2mV

06895-137

Figure 39. Positive Settling Time to 0.1%

INPUT

1V/DI

OUTPUT

ERROR BAND

VSY = ±2.5V

TIME (4µs/DIV)

+2mV

0

–2mV

06895-138

Figure 37. Negative Settling Time to 0.1%

2V/DI

ERROR BAND

TIME (4µs/DIV)

Figure 40. Negative Settling Time to 0.1%

INPUT

OUTPUT

VSY = ±8V

+2mV
0

–2mV

06895-139

Rev. F | Page 11 of 20

AD8638/AD8639

T

TA = 25°C, unless otherwise noted.

1k

VSY = ±2.5V

1k

VSY = ±8V

100

VOLTAGE NOISE DENSITY (nV/ Hz)

10

1 10010 1k 10k 25k

FREQUENCY (Hz)

06895-114

Figure 41. Voltage Noise Density vs. Frequency

1.5
VSY = ±2.5V

1.0

0.5

AGE (0.5µV/DIV)

0

–0.5

–1.0

INPUT NOISE VOL

–1.5

012345678910

TIME (Seconds)

06895-043

Figure 42. 0.1 Hz to 10 Hz Noise

1250

1000

750

500

SUPPLY CURRENT (µA)

250

+125°C

+85°C

+25°C

–40°C

100

VOLTAGE NOISE DENSITY (nV/ Hz)

10

1 10010 1k 10k 25k

FREQUENCY (Hz)

06895-115

Figure 44. Voltage Noise Density vs. Frequency

1.5
VSY = ±8V

1.0

0.5

0

–0.5

INPUT NOISE VOLTAGE (µV)

–1.0

–1.5

012345678910

TIME (Seconds)

06895-044

Figure 45. 0.1 Hz to 10 Hz Noise

1400

1200

1000

800

600

400

SUPPLY CURRENT (µA)

200

VSY = ±8V

V

SY

= ±2.5V

0

0123 564 7 8 9 10 11 12 13 14 15 16

VSY (V)

Figure 43. Supply Current vs. Supply Voltage

06895-014

0

–40 5 20 35 50 65 80 95 110–25 –10 125

TEMPERATURE (°C)

Figure 46. Supply Current vs. Temperature

06895-125

Rev. F | Page 12 of 20

AD8638/AD8639

TA = 25°C, unless otherwise noted.

–20

0

= ±8V

V

SY

A

= –10

V

–20

0

VSY = ±8V

= –100

A

V

–40

–60

–80

–100

CHANNEL SEPARATION (dB)

–120

–140

100 1k 10k 100k

FREQUENCY (Hz)

RL = 2k

RL = 10k

06895-147

Figure 47. Channel Separation vs. Frequency

0.1
VSY = ±8V

A

= +1

V

R

= 2k

L

0.01

VIN = 1V rms

0.001

THD + NOISE ( %)

VIN = 3V rms

–40

–60

–80

–100

CHANNEL SEPARATION (dB)

–120

–140

100 1k 10k 100k

FREQUENCY (Hz)

= 2k

R

L

RL = 10k

06895-148

Figure 50. Channel Separation vs. Frequency

0.1
VS = ±8V

= +1

A

V

= 10k

R

L

0.01

VIN = 1V rms

0.001

THD + NOISE ( %)

V

= 3V rms

IN

0.0001
10

100

1k 10k

FREQUENCY (Hz)

Figure 48. THD + Noise vs. Frequency

300

VSY = 16V

= 125°C

T

A

250

200

150

(pA)

B

I

100

50

0

–50

0123456789 1610 11 12 13 14 15

VCM (V)

Figure 49. Input Bias Current vs. Input Common-Mode Voltage

100k

0.0001

06895-149

10

100

1k 10k

FREQUENCY (Hz)

100k

06895-150

Figure 51. THD + Noise vs. Frequency

06895-034

Rev. F | Page 13 of 20

AD8638/AD8639

THEORY OF OPERATION

The AD8638/AD8639 are single-supply and dual-supply, ultrahigh
precision, rail-to-rail output operational amplifiers. The typical
offset voltage of 3 μV allows the amplifiers to be easily configured
for high gains without risk of excessive output voltage errors. The
extremely small temperature drift of 30 nV/°C ensures a minimum
offset voltage error over the entire temperature range of −40°C
to +125°C, making the amplifiers ideal for a variety of sensitive
measurement applications in harsh operating environments.

The AD8638/AD8639 achieve a high degree of precision
through a patented auto-zeroing topology. This unique
topology allows the AD8638/AD8639 to maintain low offset
voltage over a wide temperature range and over the operating
lifetime. The AD8638/AD8639 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 AD8638/AD8639
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 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 AD8638 is among the few auto-zero amplifiers offered in
the 5-lead SOT-23 package. This provides significant improve­ment over the ac parameters of previous auto-zero amplifiers. The
AD8638/AD8639 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 ranging from 5 kHz
to 10 kHz, the AD8638/AD8639 provide true 16-bit accuracy,
making this device 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 microvolts or more and, when
amplified by the closed-loop gain of the circuit, can show up
as a large output signal. For example, when an amplifier with
5 μV p-p 1/f noise is configured for a gain of 1000, its output has
5 mV of error due to the 1/f noise. However, the AD8638/AD8639
eliminate 1/f noise internally and thus significantly reduce
output errors.

The internal elimination of 1/f noise is accomplished as follows:
1/f noise appears as a slowly varying offset to AD8638/AD8639
inputs. Auto-zeroing corrects any dc or low frequency offset.
Therefore, the 1/f noise component is essentially removed,
leaving the AD8638/AD8639 free of 1/f noise.

INPUT VOLTAGE RANGE

The AD8638/AD8639 are not rail-to-rail input amplifiers;
therefore, care is required to ensure that both inputs do not
exceed the input voltage range. 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 the input voltage range, the loop opens and 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 they 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 may flow through these diodes, causing
permanent damage to the device. If inputs are subject to over­voltage, insert appropriate series resistors to limit the diode
current to less than 10 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 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 AD8638/AD8639 amplifiers have been carefully designed
to prevent any output phase reversal if both inputs are main­tained within the specified input voltage range. If one or both
inputs exceed the input voltage range but remain within the
supply rails, an internal loop opens and the output varies.
Therefore, the inputs should always be less than at least 2 V
below the positive supply.

OVERLOAD RECOVERY TIME

Many auto-zero amplifiers are plagued by a long overload recovery
time, often in milliseconds, due to the complicated settling
behavior of the internal nulling loops after saturation of the
outputs. The AD8638/AD8639 are designed so that internal
settling occurs within two clock cycles after output saturation
happens. This results in a much shorter recovery time, less than
50 μs, when compared to other auto-zero amplifiers. The wide
bandwidth of the AD8638/AD8639 enhances performance when
the parts 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.

Rev. F | Page 14 of 20

AD8638/AD8639

(

V

INFRARED SENSORS

Infrared (IR) sensors, particularly thermopiles, are increasingly
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, as shown in Figure 52, low
offset and drift prevent the output of the input amplifier from
drifting close to saturation. The low input bias currents generate
minimal errors from the output impedance of the sensor.
Similar to pressure sensors, the very low amplifier drift with
time and temperature eliminates additional errors once the
system is calibrated at room temperature. The low 1/f noise
improves SNR for dc measurements taken over periods often
exceeding one-fifth of a second.

Figure 52 shows a circuit that can amplify ac signals from
100 μV to 300 μV up to the 1 V to 3 V levels, with a gain of
10,000 for accurate analog-to-digital conversions.

100

100µV TO 300µ V

IR

DETECTOR

100k

5V TO 16V

1/2 AD8639

f

 1.6Hz

C

10µF

10k

TO BIAS

VOLTAGE

Figure 52. AD8639 Used as a Preamplifier for Thermopile

100k10k

5V TO 16V

1/2 AD8639

06895-065

PRECISION CURRENT SHUNT SENSOR

A precision current shunt sensor benefits from the unique
attributes of auto-zero amplifiers when used in a differencing
configuration, as shown in Figure 53. Current shunt 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

SUPPLY

e = 1000 RSI =
100mV/mA

S

0.1

I

100100k

C

5V TO 16V

AD8638

100100k

C

Figure 53. Low-Side Current Sensing

R

L

06895-066

Rev. F | Page 15 of 20

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
while saving power. A typical shunt may be 0.1 Ω. At measured
current values of 1 A, the output signal of the shunt is hundreds
of millivolts, or even volts, 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 to prevent injected bias current
from becoming a significant percentage of the measured current.
High open-loop gain, CMRR, and PSRR help to maintain the
overall circuit accuracy. With the extremely high CMRR of the
AD8638/AD8639, the CMRR is limited by the resistor ratio
matching. 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 AD8638/AD8639 can be 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 operating 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 offset error when multiplied
by the DAC output impedance (approximately 6 kΩ).

Rail-to-rail output provides full-scale output with very little
error. Output impedance of the DAC is constant and code­independent, but the high input impedance of the AD8638/
AD8639 minimizes gain errors. The wide bandwidth of the
amplifier also serves well in this case. The amplifier, with a
settling time of 4 μs, adds another time constant to the system,
increasing the settling time of the output. For example, see
Figure 54. The settling time of the AD5541 is 1 μs. The
combined settling time is approximately 4.1 μs, as can be
derived from the following equation:

22

()

0.1µF

SERIAL

INTERFACE

*AD5542 ONLY

)

()

+=

SSS

5V

REF(REFF*) REFS*

V

DD

CS
DIN

AD5541/AD5542

SCLK
LDAC*

DGND

2.5

0.1µF

AGND

Figure 54. AD8638 Used as an Output Amplifier

8638ADtDACtTOTALt

62

ADR421

4

0.1µF

5V TO 16V

AD8638

V

OUT

5V TO 16V

UNIPOLAR

OUTPUT

06895-067

AD8638/AD8639

0

0

OUTLINE DIMENSIONS

3.00

2.90

2.80

1.70

1.60

1.50

1.30

1.15

0.90

.15 MAX
.05 MIN

COPLANARITY

5

123

4

1.90

BSC

0.50 MAX

0.35 MIN

COMPLIANT TO JEDEC STANDARDS MO-178-AA

0.95 BSC

1.45 MAX

0.95 MIN

3.00

2.80

2.60

SEATING
PLANE

0.20 MAX

0.08 MIN

Figure 55. 5-Lead Small Outline Transistor Package [SOT-23]

(RJ-5)

Dimensions shown in millimeters

5.00(0.1968)

4.80(0.1890)

4.00 (0.1574)

3.80 (0.1497)

0.25 (0.0098)

0.10 (0.0040)

0.10
SEATING

PLANE

85

1

1.27 (0.0500)
BSC

6.20 (0.2441)

5.80 (0.2284)

4

1.75 (0.0688)

1.35 (0.0532)

0.51 (0.0201)

0.31 (0.0122)

8°
0°

0.25 (0.0098)

0.17 (0.0067)

10°

5°
0°

0.50 (0.0196)

0.25 (0.0099)

0.20

BSC

1.27 (0.0500)

0.40 (0.0157)

45°

0.55

0.45

0.35

121608-A

CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES)ARE ROUNDED-OFF MILLIMETER EQUIVALENTSFOR
REFERENCE ONLYAND ARE NOTAPPROPRIATE FOR USE IN DESIGN.

COMPLIANT TO JEDEC STANDARDS MS-012-AA

Figure 56. 8-Lead Standard Small Outline Package [SOIC_N]

Narrow Body

(R-8)

Dimensions shown in millimeters and (inches)

Rev. F | Page 16 of 20

012407-A

AD8638/AD8639

3.20

3.00

2.80

PIN 1

IDENTIFIER

0.95

0.85

0.75

0.15

0.05

COPLANARITY

0.10

3.20

3.00

2.80

8

5

5.15

4.90

4

0.40

0.25

4.65

1.10 MAX

15° MAX

6°
0°

0.23

0.09

1

0.65 BSC

COMPLIANT TO JEDEC STANDARDS MO-187-AA

0.80

0.55

0.40

100709-B

Figure 57. 8-Lead Mini Small Outline Package [MSOP]

(RM-8)

Dimensions shown in millimeters

2.48

2.38

2.23

5

EXPOSED

PAD

4

BOTTOM VIEW

0.08

8

1.74

1.64

1

FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFERTO
THE PIN CONFIGURATION
SECTIONOFTHISDATASHEET.

1.49

PIN 1
INDICATOR
(R 0.2)

112008-A

0.80

0.75

0.70

SEATING

PLANE

3.00

BSC SQ

0.50

0.40

INDEX

AREA

TOP VIEW

0.80 MAX

0.55 NOM

0.30

0.50 BSC

0.25

0.18

COMPLIANTTOJEDEC STANDARDS MO-229-WEED-4

0.30

0.05 MAX

0.02 NOM
COPLANARITY

0.20 REF

Figure 58. 8-Lead Lead Frame Chip Scale Package [LFCSP_WD]

3 mm × 3 mm Body, Very Very Thin, Dual Lead

(CP-8-5)

Dimensions shown in millimeters

Rev. F | Page 17 of 20

AD8638/AD8639

ORDERING GUIDE

1, 2

Model

AD8638ARJZ-R2 −40°C to +125°C 5-Lead SOT-23 RJ-5 A1T
AD8638ARJZ-REEL −40°C to +125°C 5-Lead SOT-23 RJ-5 A1T
AD8638ARJZ-REEL7 −40°C to +125°C 5-Lead SOT-23 RJ-5 A1T
AD8638ARZ −40°C to +125°C 8-Lead SOIC_N R-8
AD8638ARZ-REEL −40°C to +125°C 8-Lead SOIC_N R-8
AD8638ARZ-REEL7 −40°C to +125°C 8-Lead SOIC_N R-8
AD8639ACPZ-R2 −40°C to +125°C 8-Lead LFCSP_WD CP-8-5 A1Y
AD8639ACPZ-REEL −40°C to +125°C 8-Lead LFCSP_WD CP-8-5 A1Y
AD8639ACPZ-REEL7 −40°C to +125°C 8-Lead LFCSP_WD CP-8-5 A1Y
AD8639ARZ −40°C to +125°C 8-Lead SOIC_N R-8
AD8639ARZ-REEL −40°C to +125°C 8-Lead SOIC_N R-8
AD8639ARZ-REEL7 −40°C to +125°C 8-Lead SOIC_N R-8
AD8639ARMZ −40°C to +125°C 8-Lead MSOP RM-8 A1Y
AD8639ARMZ-REEL −40°C to +125°C 8-Lead MSOP RM-8 A1Y
AD8639ARMZ-R7 −40°C to +125°C 8-Lead MSOP RM-8 A1Y
AD8639WARZ −40°C to +125°C 8-Lead SOIC_N R-8
AD8639WARZ-RL −40°C to +125°C 8-Lead SOIC_N R-8
AD8639WARZ-R7 −40°C to +125°C 8-Lead SOIC_N R-8

1

Z = RoHS Compliant Part.

2

W = Qualified for Automotive Applications.

AUTOMOTIVE PRODUCTS

The AD8639W models are available with controlled manufacturing to support the quality and reliability requirements of automotive
applications. Note that these automotive models may have specifications that differ from the commercial models; therefore, designers
should review the Specifications section of this data sheet carefully. Only the automotive grade products shown are available for use in
automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to
obtain the specific Automotive Reliability reports for these models.

Temperature Range Package Description Package Option Branding

Rev. F | Page 18 of 20

AD8638/AD8639

NOTES

Rev. F | Page 19 of 20

AD8638/AD8639

NOTES

©2007–2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D06895-0-6/10(F)

Rev. F | Page 20 of 20