ANALOG DEVICES AD8628, AD8630 Service Manual

Zero-Drift, Single-Supply, Rail-to-Rail

O

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: 130 dB Very low input bias current: 100 pA maximum Low supply current: 1.0 mA Overload recovery time: 50 μs No external components required

APPLICATIONS

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

GENERAL DESCRIPTION

This amplifier has ultralow offset, drift, and bias current. The AD8628/AD8629/AD8630 are wide bandwidth auto-zero amplifiers featuring rail-to-rail input and output swing 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/AD8630 provide benefits previously found only in expensive auto-zeroing or chopper-stabilized amplifiers. Using Analog Devices, Inc., topology, these zerodrift amplifiers combine low cost with high accuracy and low noise. No external capacitor is required. In addition, the AD8628/ AD8629/AD8630 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 V/°C, and noise of only 0.5 µV p-p (0 Hz to 10 Hz), the AD8628/ AD8629/AD8630 are suited for applications where 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/AD8630 to reduce input biasing complexity and maximize SNR.

Input/Output Operational Amplifier

AD8628/AD8629/AD8630

PIN CONFIGURATIONS

UT

1

AD8628

TOP VIEW

V–

2

(Not to Scale)

+IN

3

Figure 1. 5-Lead TSOT (UJ-5) and 5-Lead SOT-23 (RJ-5)

NC

1

AD8628

–IN

2

+IN

3

TOP VIEW

(Not to Scal e)

4

V–

NC = NO CONNECT

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

OUT A

1

V–

AD8629

2

TOP VIEW

3

(Not to Scale)

4

–IN A

+IN A

Figure 3. 8-Lead SOIC_N (R-8) and 8-Lead MSOP (RM-8)

1

OUT A

–IN A

2

3

+IN A

+IN B

–IN B

OUT B

V+

AD8630

TOP VIEW

4

(Not to Scale)

5

6

7

Figure 4. 14-Lead SOIC_N (R-14) and 14-Lead TSSOP (RU-14)

The AD8628/AD8629/AD8630 are specified for the extended industrial temperature range (−40°C to +125°C). The AD8628 is available in tiny 5-lead TSOT, 5-lead SOT-23, and 8-lead narrow SOIC plastic packages. The AD8629 is available in the standard 8-lead narrow SOIC and MSOP plastic packages. The AD8630 quad amplifier is available in 14-lead narrow SOIC and 14-lead TSSOP plastic packages.

V+

5

–IN

4

02735-001

NC

8

V+

7

OUT

6

5

NC

02735-002

V+

8

OUT B

7

–IN B

6

5

+IN B

02735-063

OUT D

14

–IN D

13

12

+IN D

V–

11

10

+IN C

–IN C

9

OUT C

8

02735-066

Rev. G

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.

AD8628/AD8629/AD8630

REVISION HISTORY

6/08—Rev. F to Rev. G

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

Changes to Table 5 and Figure 42 Caption ................................. 12

Changes to 1/f Noise Section and Figure 49 ............................... 14

Changes to Figure 51 Caption and Figure 55 ............................. 15

Changes to Figure 57 Caption and Figure 58 Caption .............. 16

Changes to Figure 60 Caption and Figure 61 Caption .............. 17

Changes to Figure 64 ...................................................................... 18

2/08—Rev. E to Rev. F

Renamed TSOT-23 to TSOT ............................................ Universal

Deleted Figure 4 and Figure 6 ......................................................... 1

Changes to Figure 3 and Figure 4 Captions .................................. 1

Changes to Table 1 ............................................................................ 3

Changes to Table 2 ............................................................................ 4

Changes to Table 4 ............................................................................ 5

Updated Outline Dimensions ....................................................... 19

Changes to Ordering Guide .......................................................... 20

5/05—Rev. D to Rev. E

Changes to Ordering Guide .......................................................... 22

1/05—Rev. C to Rev. D

Added AD8630 ................................................................... Universal

Added Figure 5 and Figure 6 ........................................................... 1

Changes to Caption in Figure 8 and Figure 9 ............................... 7

Changes to Caption in Figure 14 .................................................... 8

Changes to Figure 17 ........................................................................ 8

Changes to Figure 23 and Figure 24 ............................................... 9

Changes to Figure 25 and Figure 26 ............................................. 10

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 Shunt Sensor ............................................... 18

Output Amplifier for High Precision DACs ........................... 18

Outline Dimensions ....................................................................... 19

Ordering Guide .......................................................................... 20

Changes to Figure 31 ...................................................................... 11

Changes to Figure 40, Figure 41, Figure 42 ................................. 12

Changes to Figure 43 and Figure 44............................................. 13

Changes to Figure 51 ...................................................................... 15

Updated Outline Dimensions ....................................................... 20

Changes to Ordering Guide .......................................................... 20

10/04—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 .......................................................... 22

10/03—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—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. G | Page 2 of 20

AD8628/AD8629/AD8630

SPECIFICATIONS

ELECTRICAL CHARACTERISTICS—VS = 5.0 V

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

Input Bias Current IB

AD8628/AD8629 AD8630

Input Offset Current IOS

Input Voltage Range Common-Mode Rejection Ratio CMRR VCM = 0 V to 5 V 120 140

Large Signal Voltage Gain AVO R

Offset Voltage Drift ∆VOS/∆T −40°C ≤ TA ≤ +125°C

OUTPUT CHARACTERISTICS

Output Voltage High VOH R

Output Voltage Low VOL R

Short-Circuit Limit ISC

Output Current IO

POWER SUPPLY

Power Supply Rejection Ratio PSRR VS = 2.7 V to 5.5 V, −40°C ≤ TA ≤ +125°C 115 130 Supply Current per Amplifier ISY V

INPUT CAPACITANCE CIN

Differential Common Mode

DYNAMIC PERFORMANCE

Slew Rate SR RL = 10 kΩ Overload Recovery Time Gain Bandwidth Product GBP

NOISE PERFORMANCE

Voltage Noise en p-p 0.1 Hz to 10 Hz

0.1 Hz to 1.0 Hz Voltage Noise Density en f = 1 kHz Current Noise Density in f = 10 Hz

−40°C ≤ TA ≤ +125°C

−40°C ≤ TA ≤ +125°C 115 130 = 10 kΩ, VO = 0.3 V to 4.7 V 125 145

L

−40°C ≤ TA ≤ +125°C 120 135

= 100 kΩ to ground 4.99 4.996

L

−40°C ≤ TA ≤ +125°C 4.99 4.995

RL = 10 kΩ to ground 4.95 4.98

−40°C ≤ TA ≤ +125°C 4.95 4.97 = 100 kΩ to V+

L

−40°C ≤ TA ≤ +125°C

RL = 10 kΩ to V+

−40°C ≤ TA ≤ +125°C

= VS/2 0.85 1.1 mA

O

−40°C ≤ TA ≤ +125°C

0

±25 ±50

1 5 μV

10 μV

30 100 pA 100 300 pA

1.5 nA

50 200 pA

250 pA

0.002 0.02 μV/°C

1 5 mV 2 5 mV 10 20 mV 15 20 mV

±40 ±30 ±15

1.0 1.2 mA

1.5

8.0

1.0

0.05

2.5

0.5

0.16 22 5

5 V

dB dB dB dB

V V V V

mA mA mA mA

dB

pF pF

V/μs ms MHz

μV p-p μV p-p nV/√Hz fA/√Hz

Rev. G | Page 3 of 20

AD8628/AD8629/AD8630

ELECTRICAL CHARACTERISTICS—VS = 2.7 V

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

AD8628/AD8629 30 100 pA AD8630 100 300 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 2.7 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 R

−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 R

−40°C ≤ TA ≤ +125°C 2.68 2.695 V R

−40°C ≤ TA ≤ +125°C 2.67 2.675 V Output Voltage Low VOL R

−40°C ≤ TA ≤ +125°C 2 5 mV R

−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 per Amplifier ISY V

−40°C ≤ TA ≤ +125°C 0.9 1.2 mA

INPUT CAPACITANCE CIN

Differential 1.5 pF Common Mode 8.0 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 en f = 1 kHz 22 nV/√Hz Current Noise Density in f = 10 Hz 5 fA/√Hz

= 10 kΩ, VO = 0.3 V to 2.4 V 110 140 dB

L

= 100 kΩ to ground 2.68 2.695 V

L

= 10 kΩ to ground 2.67 2.68 V

L

= 100 kΩ to V+ 1 5 mV

L

= 10 kΩ to V+ 10 20 mV

L

= VS/2 0.75 1.0 mA

O

Rev. G | Page 4 of 20

AD8628/AD8629/AD8630

ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

Supply Voltage 6 V Input Voltage GND − 0.3 V to VS + 0.3 V Differential Input Voltage 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

Differential input voltage is limited to ±5 V or the supply voltage, whichever

is less.

1

±5.0 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 CHARACTERISTICS

θJA is specified for worst-case conditions, that is, θJA is specified for the device soldered in a circuit board for surface-mount packages. This was measured using a standard two-layer board.

Table 4.

Package Type θJA θJC Unit

5-Lead TSOT (UJ-5) 207 61 °C/W 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) 190 44 °C/W 14-Lead SOIC_N (R-14) 105 43 °C/W 14-Lead TSSOP (RU-14) 148 23 °C/W

ESD CAUTION

Rev. G | Page 5 of 20

AD8628/AD8629/AD8630

TYPICAL PERFORMANCE CHARACTERISTICS

180

VS = 2.7V T

= 25°C

160

A

140

120

100

80

60

NUMBER OF AMPLIF IERS

40

20

0 –2.5 –1.5 –0. 5 0.5 1.5 2.5

INPUT OFFSET VOLTAGE (µV)

Figure 5. Input Offset Voltage Distribution

02735-003

100

VS = 5V

90

V

= 2.5V

CM

T

= 25°C

A

80

70

60

50

40

30

NUMBER OF AMPLIF IERS

20

10

0 –2.5 –1.5 –0.5 0.5 1.5 2.5

INPUT OFFSET VOLTAGE (µV)

Figure 8. Input Offset Voltage Distribution

02735-006

60

VS = 5V

50

40

30

20

INPUT BIAS CURRENT (pA)

10

0

012345

INPUT COMMON-MODE VOLTAGE (V)

+85°C

+25°C

–40°C

6

Figure 6. AD8628 Input Bias Current vs. Input Common-Mode Voltage

1500

VS = 5V

1000

500

0

–500

INPUT BIAS CURRENT (pA)

–1000

150°C

125°C

7

VS = 5V T

= –40°C TO +125° C

6

A

5

4

3

2

NUMBER OF AMPLIF IERS

1

0

02735-004

0

2

4

TCVOS (nV/°C)

68

10

02735-007

Figure 9. Input Offset Voltage Drift

1k

VS = 5V T

= 25°C

A

100

10

1

OUTPUT VOLTAGE (mV)

0.1

SOURCE

SINK

–1500

012345

INPUT COMMON-MODE VOLTAGE (V)

6

Figure 7. AD8628 Input Bias Current vs. Input Common-Mode Voltage

02735-005

Rev. G | Page 6 of 20

0.01

0.0001 0.001 0.10.01 1 10 LOAD CURRENT (mA)

Figure 10. Output Voltage to Supply Rail vs. Load Current

02735-008

AD8628/AD8629/AD8630

1k

VS = 2.7V

100

10

1

OUTPUT VOLTAGE (mV)

0.1

0.01

0.0001 0.001 0.10.01 1 10

SOURCE

SINK

LOAD CURRENT (mA)

Figure 11. Output Voltage to Supply Rail vs. Load Current

1500

VS = 5V

= 2.5V

V

CM

= –40°C TO + 150°C

T

A

1150

900

450

INPUT BIAS CURRENT (pA)

100

0

–50 0 25–25 50 75 100 125 150 175

TEMPERATURE (°C)

Figure 12. AD8628 Input Bias Current vs. Temperature

02735-009

02735-010

1000

TA = 25°C

800

600

400

SUPPLY CURRENT (µA)

200

0

012 4536

SUPPLY VOLTAGE (V)

02735-012

Figure 14. Supply Current vs. Supply Voltage

60

40

20

0

OPEN-LOOP GAIN (dB)

–20

10k 100k 1M 10M

GAIN

PHASE

FREQUENCY (Hz)

VS = 2.7V C

= 20pF

L

R

= ∞

L

Ф

= 45°

M

0

45

90

135

180

225

PHASE SHIFT (Degrees)

02735-013

Figure 15. Open-Loop Gain and Phase vs. Frequency

1250

TA = 25°C

1000

750

500

SUPPLY CURRENT (µA)

250

0

–50 0 50 150100 200

TEMPERATURE (°

5V

2.7V

C

)

Figure 13. Supply Current vs. Temperature

02735-011

Rev. G | Page 7 of 20

70

60

50

40

30

20

10

0

OPEN-LOOP GAIN (dB)

–10

–20

–30

10k 100k 1M 10M

GAIN

PHASE

FREQUENCY (Hz)

Figure 16. Open-Loop Gain and Phase vs. Frequency

VS = 5V C

= 20pF

L

R

= ∞

L

Φ

= 52.1°

M

0

45

90

135

180

225

PHASE SHIF T (Degrees)

02735-014

AD8628/AD8629/AD8630

70

60

50

AV = 100

40

30

AV = 10

20

10

AV = 1

0

CLOSED-LOOP GAIN (dB)

–10

–20

–30

1k 10k 100k 1M 10M

FREQUENCY ( Hz)

Figure 17. Closed-Loop Gain vs. Frequency

VS = 2.7V C

= 20pF

L

R

= 2kΩ

L

02735-015

300

VS = 5V

270

240

210

180

150

120

90

OUTPUT IMPEDANCE (Ω)

60

30

0

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

AV = 100

AV = 10

AV = 1

FREQUENCY ( Hz)

Figure 20. Output Impedance vs. Frequency

02735-018

70

60

50

40

30

20

10

CLOSED-LOOP GAIN (dB)

–10

–20

–30

= 100

A

V

AV = 10

AV = 1

0

1k 10k 100k 1M 10M

FREQUENCY ( Hz)

Figure 18. Closed-Loop Gain vs. Frequency

300

VS = 2.7V

270

240

210

180

150

120

90

OUTPUT IMPEDANCE (Ω)

60

30

0

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

AV = 100

= 10

A

V

FREQUENCY (Hz)

AV = 1

Figure 19. Output Impedance vs. Frequency

VS = 5V C

= 20pF

L

R

= 2kΩ

L

VS = ±1.35V C

= 300pF

L

R

= ∞

0V

VOLTAGE (500mV/DIV)

02735-016

L

A

V

= 1

TIME (4µs/DIV)

02735-019

Figure 21. Large Signal Transient Response

VS = ±2.5V C

= 300pF

L

R

= ∞

0V

VOLTAGE (1V/DIV)

02735-017

L

A

V

= 1

TIME (5µs/DIV)

02735-020

Figure 22. Large Signal Transient Response

Rev. G | Page 8 of 20

AD8628/AD8629/AD8630

T

80

VS = ±2.5V R

= 2kΩ

L

70

T

= 25°C

A

60

50

40

30

OVERSHOOT (%)

20

OS–

OS+

10

0

110100

CAPACITIVE LOAD ( pF)

Figure 26. Small Signal Overshoot vs. Load Capacitance

1k

02735-024

AGE (50mV/DI V)

VOL

VS = ±1.35V C

= 50pF

L

R

= ∞

L

A

= 1

V

0V

TIME (4µs/DIV)

Figure 23. Small Signal Transient Response

02735-021

VS = ±2.5V C

= 50pF

L

R

= ∞

L

A

= 1

V

0V

AGE (50mV/DIV)

VOL

TIME (4µs/DIV)

Figure 24. Small Signal Transient Response

100

= ±1.35V

V

S

R

= 2kΩ

90

L

T

= 25°C

A

80

70

60

50

40

OVERSHOOT (%)

30

OS–

20

10

0

110100

CAPACITIVE LOAD ( pF)

Figure 25. Small Signal Overshoot vs. Load Capacitance

OS+

02735-022

1k

02735-023

VS = ±2.5V A

= –50

V

IN

V

R

= 10kΩ

L

C

= 0pF

L

CH1 = 50mV/DIV CH2 = 1V/DIV

0V

VOLTAGE (V)

0V

V

OUT

TIME (2µs/DIV)

02735-025

Figure 27. Positive Overvoltage Recovery

0V

VS = ±2.5V A

= –50

V

R

= 10kΩ

V

IN

V

OUT

VOLTAGE (V)

L

C

= 0pF

L

CH1 = 50mV/DIV CH2 = 1V/DIV

0V

TIME (10µ s/DIV)

02735-026

Figure 28. Negative Overvoltage Recovery

Rev. G | Page 9 of 20

AD8628/AD8629/AD8630

VS = ±2.5V V

= 1kHz @ ±3V p-p

IN

C

= 0pF

L

R

= 10kΩ

L

A

= 1

V

0V

VOLTAGE (1V/DIV)

TIME (200µs/DIV)

02735-027

Figure 29. No Phase Reversal

140

VS = ±1.35V

120

100

80

60

40

PSRR (dB)

20

0

–20

–40

–60

100 1k 10k 100k 1M 10M

FREQUENCY (Hz)

+PSRR

–PSRR

Figure 32. PSRR vs. Frequency

02735-030

140

VS = 2.7V

120

100

80

60

40

CMRR (dB)

20

0

–20

–40

–60

100 1k 10k 100k 1M 10M

FREQUENCY (Hz)

Figure 30. CMRR vs. Frequency

140

VS = 5V

120

100

80

60

40

CMRR (dB)

20

0

–20

–40

–60

100 1k 10k 100k 1M 10M

FREQUENCY (Hz)

Figure 31. CMRR vs. Frequency

140

VS = ±2.5V

120

100

80

60

40

PSRR (dB)

20

0

–20

–40

–60

02735-028

100 1k 10k 100k 1M 10M

–PSRR

FREQUENCY (Hz)

+PSRR

02735-031

Figure 33. PSRR vs. Frequency

3.0

2.5

2.0

1.5

1.0

OUTPUT SWING (V p-p)

0.5

0

02735-029

100 1k 10k 100k 1M

FREQUENCY ( Hz)

VS = 2.7V R

= 10kΩ

L

T

= 25°C

A

= 1

V

02735-032

Figure 34. Maximum Output Swing vs. Frequency

Rev. G | Page 10 of 20

AD8628/AD8629/AD8630

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

OUTPUT SWING (V p-p)

1.5

1.0

0.5

0

100 1k 10k 100k 1M

FREQUENCY ( Hz)

Figure 35. Maximum Output Swing vs. Frequency

VS = 5V R

= 10kΩ

L

T

= 25°C

A

= 1

V

02735-033

120

VS = 2.7V NOISE AT 1kHz = 21.3nV

105

90

75

60

45

30

VOLTAGE NOISE DENSITY (nV/ √Hz)

15

0

0 0. 5 1.0 1.5 2.0 2.5

FREQUENCY ( kHz)

Figure 38. Voltage Noise Density at 2.7 V from 0 Hz to 2.5 kHz

02735-036

0.60 VS = 2.7V

0.45

0.30

0.15

0

VOLTAGE (µV)

–0.15

–0.30

–0.45

–0.60

01 2345 67 8910

TIME (µs)

Figure 36. 0.1 Hz to 10 Hz Noise

0.60 VS = 5V

0.45

0.30

0.15

0

120

VS = 2.7V NOISE AT 10kHz = 42.4nV

105

90

75

60

45

30

VOLTAGE NOISE DENSITY (nV/ √Hz)

15

0

02735-034

0 5 10 15 20 25

FREQUENCY (kHz)

02735-037

Figure 39. Voltage Noise Density at 2.7 V from 0 Hz to 25 kHz

120

VS = 5V NOISE AT 1kHz = 22.1nV

105

90

75

60

VOLTAGE (µV)

–0.15

–0.30

–0.45

–0.60

01 2345 67 8910

TIME (µs)

Figure 37. 0.1 Hz to 10 Hz Noise

02735-035

Rev. G | Page 11 of 20

45

30

VOLTAGE NOISE DENSITY (nV/ √Hz)

15

0

0 0. 5 1.0 1.5 2.0 2.5

FREQUENCY ( kHz)

Figure 40. Voltage Noise Density at 5 V from 0 Hz to 2.5 kHz

02735-038

AD8628/AD8629/AD8630

120

VS = 5V NOISE AT 10kHz = 36.4nV

105

90

150

100

VS = 2.7V T

= –40°C TO +150° C

A

75

60

45

30

VOLTAGE NOISE DENSITY (nV/ √Hz)

15

0

0 5 10 15 20 25

FREQUENCY (kHz)

Figure 41. Voltage Noise Density at 5 V from 0 Hz to 25 kHz

120

VS = 5V

105

90

75

60

45

30

VOLTAGE NOISE DENSITY (nV/ √Hz)

15

0

05

FREQUENCY (kHz)

Figure 42. Voltage Noise Density at 5 V from 0 Hz to 10 kHz

OUTPUT SHO RT-CIRCUIT CURRENT (mA)

02735-039

OUTPUT SHO RT-CIRCUIT CURRENT (mA)

10

02735-040

–100

50

ISC–

0

ISC+

–50

–100

–50 25 50 750–25 100 125 150 175

TEMPERATURE (°C)

Figure 44. Output Short-Circuit Current vs. Temperature

150

VS = 5V T

= –40°C TO +150°C

A

100

ISC–

50

0

–50

ISC+

–50 25 50 750–25 100 125 150 175

TEMPERATURE (°C)

Figure 45. Output Short-Circuit Current vs. Temperature

02735-042

02735-043

150

140

130

VS = 2.7V TO 5V

120

T

= –40°C TO +125° C

A

110

100

90

80

70

POWER SUPPLY REJECTION (dB)

60

50

–50 0 25–25 50 75 100 125

TEMPERATURE (°C)

Figure 43. Power Supply Rejection vs. Temperature

02735-041

Rev. G | Page 12 of 20

1k

VS = 5V

100

VOL– VEE@ 1kΩ

10

VCC– VOH@ 100kΩ

1

OUTPUT-TO-RAIL VOLTAGE (mV)

0.1 –50 25 50 750–25 100 125 150 175

VCC– VOH@ 1kΩ

VCC– VOH@ 10kΩ

VOL– VEE@ 10kΩ

VOL– VEE@ 100kΩ

TEMPERATURE (°C)

Figure 46. Output-to-Rail Voltage vs. Temperature

02735-044

AD8628/AD8629/AD8630

R A

1k

VS = 2.7V

100

10

1

OUTPUT-TO-RAIL VOLTAGE (mV)

0.1 –50 25 50 750–25 100 125 150 175

VCC– VOH@ 1kΩ

VCC– VOH@ 10kΩ

VCC– VOH@ 100kΩ

TEMPERATURE (°C)

VOL– VEE@ 1kΩ

VOL– VEE@ 10kΩ

VOL– VEE@ 100kΩ

02735-045

Figure 47. Output-to-Rail Voltage vs. Temperature

140

120

100

TION (dB)

80

60

40

CHANNEL SEPA

20

V

IN

28mV p-p

0

1k 10k 100k 1M 10M

+2.5V

V+

+

AB

–

V–

–2.5V

FREQUENCY (Hz)

R1

10kΩ

V–

V

OUT

V+

VS = ±2.5V

R2

100Ω

Figure 48. AD8629/AD8630 Channel Separation vs. Frequency

02735-062

Rev. G | Page 13 of 20

AD8628/AD8629/AD8630

FUNCTIONAL DESCRIPTION

The AD8628/AD8629/AD8630 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 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/AD8630 achieve a high degree of precision through a patented combination of auto-zeroing and chopping. This unique topology allows the AD8628/AD8629/AD8630 to maintain their low offset voltage over a wide temperature range and over their operating lifetime. The AD8628/AD8629/AD8630 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/AD8630 family uses 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 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 package. This provides a significant improvement over the ac parameters of the previous auto-zero amplifiers. The AD8628/AD8629/AD8630 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/AD8630 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 1000, its output has 5 mV of error due to the 1/f noise. However, the AD8628/AD8629/AD8630 eliminate 1/f noise internally, thereby greatly reducing output errors.

The internal elimination of 1/f noise is accomplished as follows. 1/f noise appears as a slowly varying offset to the AD8628/AD8629/ AD8630 inputs. Auto-zeroing corrects any dc or low frequency offset. Therefore, the 1/f noise component is essentially removed, leaving the AD8628/AD8629/AD8630 free of 1/f noise.

One advantage that the AD8628/AD8629/AD8630 bring to system 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 Competitor A and Competitor B. 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.

120

COMPETITOR A

105

(89.7nV/ √Hz)

90

75

60

COMPETITOR B

45

(31.1nV/ √Hz)

30

VOLTAGE NOISE DENSI TY (nV/ √Hz)

15

AD8628 (19.4nV/ √Hz)

0

042861012

Figure 49. Noise Spectral Density of AD8628 vs. Competition

MK AT 1kHz FOR ALL 3 GRAPHS

FREQUENCY (kHz)

02735-046

Rev. G | Page 14 of 20

AD8628/AD8629/AD8630

PEAK-TO-PEAK NOISE

Because of the ping-pong action between auto-zeroing and chopping, the peak-to-peak noise of the AD8628/AD8629/ AD8630 is much lower than the competition. Figure 50 and Figure 51 show this comparison.

en p-p = 0.5µV BW = 0.1Hz TO 10Hz

VOLTAGE (0.5µV/DIV)

TIME (1s/ DIV)

Figure 50. AD8628 Peak-to-Peak Noise

en p-p = 2.3µV BW = 0.1Hz TO 10Hz

VOLTAGE (0.5µV/DIV)

50

45

40

35

30

25

NOISE (dB)

20

15

10

5

0

0 30 60 10090807050402010

FREQUENCY ( kHz)

02735-050

Figure 53. Simulation Transfer Function of the Test Circuit in Figure 52

50

45

40

02735-047

35

30

25

NOISE (dB)

20

15

10

5

0

0 30 60 10090807050402010

FREQUENCY ( kHz)

02735-051

Figure 54. Actual Transfer Function of the Test Circuit in Figure 52

The measured noise spectrum of the test circuit charted in Figure 54 shows that noise between 5 kHz and 45 kHz is successfully rolled off by the first-order filter.

TIME (1s/ DIV)

02735-048

Figure 51. Competitor A Peak-to-Peak Noise

NOISE BEHAVIOR WITH FIRST-ORDER, LOW-PASS FILTER

The AD8628 was simulated as a low-pass filter (see Figure 53) 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. Figure 53 and Figure 54 show the difference between the simulated and actual transfer functions of the circuit shown in Figure 52.

IN

100kΩ

1kΩ

Figure 52. First-Order Low-Pass Filter Test Circuit,

×101 Gain and 3 kHz Corner Frequency

470pF

OUT

02735-049

Rev. G | Page 15 of 20

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 noise of Competitor A.

10

COMPETITOR A

AD8551

1

RMS NOISE (µ V)

0.1 10 100 10k1k

3dB FILT ER BANDWIDTH (Hz)

Figure 55. RMS Noise vs. 3 dB Filter Bandwidth in Hz

AD8628

02735-052

AD8628/AD8629/AD8630

INPUT OVERVOLTAGE PROTECTION

Although the AD8628/AD8629/AD8630 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 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 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 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/AD8630 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/AD8630 have been designed so that internal settling occurs within two clock cycles after output saturation occurs. 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/AD8630 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.

V

IN

0V

VOLTAGE (V)

0V

V

OUT

TIME (500µ s/DIV)

Figure 56. Positive Input Overload Recovery for the AD8628

V

IN

0V

VOLTAGE (V)

0V

V

OUT

TIME (500µ s/DIV)

Figure 57. Positive Input Overload Recovery for Competitor A

V

IN

0V

VOLTAGE (V)

V

OUT

TIME (500µ s/DIV)

Figure 58. Positive Input Overload Recovery for Competitor B

CH1 = 50mV/DIV CH2 = 1V/DIV A

= –50

V

CH1 = 50mV/DIV CH2 = 1V/DIV A

= –50

V

CH1 = 50mV/DIV CH2 = 1V/DIV A

= –50

V

02735-053

02735-054

02735-055

Rev. G | Page 16 of 20

AD8628/AD8629/AD8630

Ω

The results shown in Figure 56 to Figure 61 are summarized in

0V

V

IN

VOLTAGE (V)

V

OUT

CH1 = 50mV/DIV CH2 = 1V/DIV A

= –50

V

Table 5.

Table 5. Overload Recovery Time

Model

Positive Overload Recovery (μs)

Negative Overload Recovery (μs)

AD8628 6 9 Competitor A 650 25,000 Competitor B 40,000 35,000

0V

TIME (500µ s/DIV)

Figure 59. Negative Input Overload Recovery for the AD8628

0V

V

IN

V

OUT

VOLTAGE (V)

0V

TIME (500µ s/DIV)

Figure 60. Negative Input Overload Recovery for Competitor A

0V

V

IN

V

OUT

CH1 = 50mV/DIV CH2 = 1V/DIV A

= –50

V

CH1 = 50mV/DIV CH2 = 1V/DIV A

= –50

V

INFRARED SENSORS

Infrared (IR) sensors, particularly thermopiles, are increasingly

02735-056

02735-057

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, as in Figure 62, 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. As with pressure sensors, the very low amplifier drift with time and temperature eliminate additional errors once the temperature measurement is calibrated. The low 1/f noise improves SNR for dc measurements taken over periods often exceeding one-fifth of a second.

Figure 62 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 conversion.

100k

5V

1/2 AD8629

02735-059

≈ 1.6Hz

f

C

10kΩ

10µF

10kΩ

TO BIAS

VOLTAGE

100Ω

100µV TO 300µV

IR

DETECT OR

100kΩ

5V

1/2 AD8629

Figure 62. AD8629 Used as Preamplifier for Thermopile

VOLTAGE (V)

0V

TIME (500µ s/DIV)

02735-058

Figure 61. Negative Input Overload Recovery for Competitor B

Rev. G | Page 17 of 20

AD8628/AD8629/AD8630

V

PRECISION CURRENT SHUNT SENSOR OUTPUT AMPLIFIER FOR HIGH PRECISION DACS

A precision current shunt sensor benefits from the unique attributes of auto-zero amplifiers when used in a differencing configuration, as shown in Figure 63. 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.

SUPPLY

e = 1000 RSI

100mV/m A

S

0.1Ω

I

100Ω100kΩ

C

5V

R

L

R

AD8628

100Ω100kΩ

C

Figure 63. Low-Side Current Sensing

02735-060

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 might 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, so that injected bias current does not become a significant percentage of the measured current. High open-loop gain, CMRR, and PSRR 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.

The AD8628/AD8629/AD8360 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 a 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. The 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. The output impedance of the DAC is constant and code independent, but the high input impedance of the AD8628/ AD8629/AD8630 minimizes gain errors. The wide bandwidth of the amplifiers 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

()( )( )

AD8628

tDACtTOTALt +=

SSS

2.5

SERIAL

INTERFACE

*AD5542 ONLY

5

0.1µF

REF(REFF*) REFS*

V

DD

CS

DIN

AD5541/AD5542

SCLK

LDAC*

DGND

Figure 64. AD8628 Used as an Output Amplifier

0.1µF

10µF

AGND

V

AD8628

OUT

UNIPOLAR

OUTPUT

02735-061

Rev. G | Page 18 of 20

AD8628/AD8629/AD8630

OUTLINE DIMENSIONS

2.90 BSC

5.00 (0.1968)

4.80 (0.1890)

54

0.50

0.30

2.80 BSC

0.95 BSC

*

1.00 MAX

SEATING PLANE

0.20

0.08

8° 4° 0°

1.60 BSC

*

0.90

0.87

0.84

0.10 MAX

123

PIN 1

1.90

BSC

*

COMPLIANT TO JEDEC STANDARDS MO-193-AB WITH THE EXCEPTION OF PACKAGE HEIGHT AND THICKNESS.

Figure 65. 5-Lead Thin Small Outline Transistor Package [TSOT]

(UJ-5)

Dimensions shown in millimeters

2.90 BSC

1.60 BSC

1.30

1.15

0.90

0.15 MAX

5

123

PIN 1

COMPLIANT TO JEDEC STANDARDS MO-178-A A

1.90

BSC

0.50

0.30

4

0.95 BSC

2.80 BSC

1.45 MAX

SEATING PLANE

0.22

0.08

10°

5° 0°

Figure 66. 5-Lead Small Outline Transistor Package [SOT-23]

(RJ-5)

Dimensions shown in millimeters

0.60

0.45

0.30

0.60

0.45

0.30

4.00 (0.1574)

3.80 (0.1497)

0.25 (0.0098)

0.10 (0.0040)

COPLANARI TY

0.10

CONTROL LING DIMENSI ONS ARE IN MILL IMET ERS; INCH DI MENSIO NS (IN PARENTHESES ) ARE ROUNDED- OFF MI LLI METER EQ UIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRI ATE FOR USE I N DESIG N.

85

1

1.27 (0.0500)

SEATING

PLANE

COMPLI ANT TO JEDE C STANDARDS MS-012-A A

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)

0.50 (0.0196)

0.25 (0.0099)

1.27 (0.0500)

0.40 (0.0157)

45°

012407-A

Figure 67. 8-Lead Standard Small Outline Package [SOIC_N]

Narrow Body

(R-8)

Dimensions shown in millimeters and (inches)

3.20

3.00

2.80

8

5

4

SEATING PLANE

5.15

4.90

4.65

1.10 MAX

0.23

0.08

8° 0°

0.80

0.60

0.40

3.20

3.00

1

2.80

PIN 1

0.65 BSC

0.95

0.85

0.75

0.15

0.38

0.00

0.22

COPLANARITY

0.10

COMPLIANT TO JEDEC STANDARDS MO-187-AA

Figure 68. 8-Lead Mini Small Outline Package [MSOP]

(RM-8)

Dimensions shown in millimeters

Rev. G | Page 19 of 20

AD8628/AD8629/AD8630

5.10

8.75 (0.3445)

8.55 (0.3366)

BSC

8

7

6.20 (0.2441)

5.80 (0.2283)

1.75 (0.0689)

1.35 (0.0531)

SEATING PLANE

8° 0°

0.25 (0.0098)

0.17 (0.0067)

0.50 (0.0197)

0.25 (0.0098)

1.27 (0.0500)

0.40 (0.0157)

4.50

4.40

45°

4.30

PIN 1

1.05

1.00

0.80

060606-A

Figure 70. 14-Lead Thin Shrink Small Outline Package [TSSOP]

4.00 (0.1575)

3.80 (0.1496)

0.25 (0.0098)

0.10 (0.0039)

COPLANARIT Y

0.10

14

1

1.27 (0.0500)

0.51 (0.0201)

0.31 (0.0122)

CONTROLL ING DIMENS IONS ARE IN MILLIM ETERS; INCH DI MENSIONS (IN PARENTHESES) ARE ROUNDED- OFF MIL LIMET ER EQUIVALENTS FOR REFERENCE ON LY AND ARE NOT APPROPRI ATE FOR USE IN DES IGN.

COMPLIANT TO JEDEC STANDARDS MS-012-AB

Figure 69. 14-Lead Standard Small Outline Package [SOIC_N]

Narrow Body (R-14)

Dimensions shown in millimeters and (inches)

ORDERING GUIDE

Model Temperature Range Package Description Package Option Branding

AD8628AUJ-R2 −40°C to +125°C 5-Lead TSOT UJ-5 AYB AD8628AUJ-REEL −40°C to +125°C 5-Lead TSOT UJ-5 AYB AD8628AUJ-REEL7 −40°C to +125°C 5-Lead TSOT UJ-5 AYB AD8628AUJZ-R2 AD8628AUJZ-REEL AD8628AUJZ-REEL7 AD8628AR −40°C to +125°C 8-Lead SOIC_N R-8 AD8628AR-REEL −40°C to +125°C 8-Lead SOIC_N R-8 AD8628AR-REEL7 −40°C to +125°C 8-Lead SOIC_N R-8 AD8628ARZ AD8628ARZ-REEL AD8628ARZ-REEL7 AD8628ART-R2 −40°C to +125°C 5-Lead SOT-23 RJ-5 AYA AD8628ART-REEL7 −40°C to +125°C 5-Lead SOT-23 RJ-5 AYA AD8628ARTZ-R2 AD8628ARTZ-REEL7 AD8629ARZ AD8629ARZ-REEL AD8629ARZ-REEL7 AD8629ARMZ-R2 AD8629ARMZ-REEL AD8630ARUZ AD8630ARUZ-REEL AD8630ARZ AD8630ARZ-REEL AD8630ARZ-REEL7

1

Z = RoHS Compliant Part.

1

−40°C to +125°C 5-Lead TSOT UJ-5 A0L

1

−40°C to +125°C 5-Lead TSOT UJ-5 A0L

1

−40°C to +125°C 5-Lead TSOT UJ-5 A0L

1