AD8270ACPZ-R7_技术文档

Precision Dual-Channel,

Difference Amplifier

AD8270

FUNCTIONAL BLOCK DIAGRAM

FEATURES

With no external resistors

Difference amplifier: gains of 0.5, 1, or 2

Single ended amplifiers: over 40 different gains

Set reference voltage at midsupply

Excellent ac specifications

15 MHz bandwidth

30 V/μs slew rate

10kΩ

–IN1A 1

–IN2A 2

+IN2A 3

+IN1A 4

12 –IN1B

11 –IN2B

10 +IN2B

_

+

_

+

High accuracy dc performance

0.08% maximum gain error

10kΩ

10 ppm/°C maximum gain drift

80 dB minimum CMRR (G = 2)

Two channels in small 4 mm × 4 mm LFCSP

Supply current: 2.5 mA per channel

Supply range: 2.5 V to 18 V

AD8270

9

+IN1B

20kΩ 20kΩ

APPLICATIONS

Instrumentation amplifier building blocks

Level translators

Figure 1.

Automatic test equipment

High performance audio

Sine/Cosine encoders

GENERAL DESCRIPTION

Table 1. Difference Amplifiers by Category

The AD8270 is a low distortion, dual-channel amplifier with

internal gain setting resistors. With no external components,

it can be configured as a high performance difference amplifier

with gains of 0.5, 1, or 2. It can also be configured in over 40 single-

ended configurations, with gains ranging from −2 to +3.

High

Speed

High

Voltage

Single-Supply

Unidirectional

Single-Supply

Bidirectional

AD8270

AD8273

AMP03

AD628

AD629

AD8202

AD8203

AD8205

AD8206

AD8216

The AD8270 is the first dual-difference amplifier in the small

4 mm × 4 mm LFCSP. It requires the same board area as a typical

single-difference amplifier. The smaller package allows a 2×

increase in channel density and a lower cost per channel, all

with no compromise in performance.

The AD8270 operates on both single and dual supplies and

requires only 2.5 mA maximum supply current for each ampli-

fier. It is specified over the industrial temperature range of

−40°C to +85°C and is fully RoHS compliant.

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarks and registeredtrademarks arethe property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700

Fax: 781.461.3113

www.analog.com

AD8270

TABLE OF CONTENTS

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

Circuit Information.................................................................... 13

Driving the AD8270................................................................... 13

Package Considerations............................................................. 13

Power Supplies............................................................................ 13

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

Applications Information.............................................................. 15

Difference Amplifier Configurations ...................................... 15

Single-Ended Configurations ................................................... 15

Differential Output .................................................................... 17

Driving an ADC ......................................................................... 18

Driving Cabling.......................................................................... 18

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

Ordering Guide .......................................................................... 19

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

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

Functional Block Diagram .............................................................. 1

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

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

Difference Amplifier Configurations ........................................ 3

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

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

Maximum Power Dissipation ..................................................... 5

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

Pin Configuration and Function Descriptions............................. 6

Typical Performance Characteristics ............................................. 7

Theory of Operation ...................................................................... 13

REVISION HISTORY

1/08—Revision 0: Initial Version

Rev. 0 | Page 2 of 20

AD8270

SPECIFICATIONS

DIFFERENCE AMPLIFIER CONFIGURATIONS

V_S= 15 V, V_REF= 0 V, T_A= 25°C, R_LOAD= 2 kΩ, specifications referred to input, unless otherwise noted.

Table 2.

G = 0.5

G = 1

G = 2

Parameter

Conditions

Min

Typ Max

Min

Typ Max

Min

Typ Max

Unit

DYNAMIC PERFORMANCE

Bandwidth

Slew Rate

Settling Time to 0.01%

Settling Time to 0.001%

NOISE/DISTORTION

Harmonic Distortion

20

30

15

30

10

30

MHz

V/μs

ns

10 V step on output

700 800

750 900

700 800

750 900

700 800

750 900

ns

f = 1 kHz, V_OUT= 10 V p-p,

R_LOAD= 600 Ω

f = 0.1 Hz to 10 Hz

f = 1 kHz

84

145

95

dB

Voltage Noise¹

2

1.5

38

1

μV p-p

52

26

nV/√Hz

GAIN

Gain Error

0.08

%

Gain Drift

T_A= −40°C to +85°C

1

10

1

10

1

10

ppm/°C

INPUT CHARACTERISTICS

Offset²

450 1500

300 1000

225 750

μV

Average Temperature Drift T_A= −40°C to +85°C

3

86

2

92

1.5

98

μV/°C

dB

Common-Mode Rejection

Ratio

DC to 1 kHz

70

76

80

Power Supply Rejection Ratio

Input Voltage Range³

Common-Mode Resistance⁴

Bias Current

2

10

2

10

2

10

+15.4

μV/V

V

kΩ

nA

−15.4

+15.4 −15.4

7.5

10

7.5

500

OUTPUT CHARACTERISTICS

Output Swing

−13.8

−13.7

+13.8 −13.8

+13.7 −13.7

+13.8 −13.8

+13.7 −13.7

+13.8

+13.7

V

mA

T_A= −40°C to +85°C

Sourcing

Sinking

Short-Circuit Current Limit

100

60

100

60

100

60

POWER SUPPLY

Supply Current

(per Amplifier)

2.3

2.5

3

2.3

2.5

3

2.3

2.5

3

mA

T_A= −40°C to +85°C

¹Includes amplifier voltage and current noise, as well as noise of internal resistors.

²Includes input bias and offset errors.

³At voltages beyond the rails, internal ESD diodes begin to turn on. In some configurations, the input voltage range may be limited by the internal op amp (see the

Input Voltage Range section for details).

⁴Internal resistors are trimmed to be ratio matched but have 20% absolute accuracy. Common-mode resistance was calculated with both inputs in parallel. Common-

mode impedance at only one input is 2× the resistance listed.

Rev. 0 | Page 3 of 20

AD8270

V_S= 5 V, V_REF= 0 V, T_A= 25°C, R_LOAD= 2 kΩ, specifications referred to input, unless otherwise noted.

Table 3.

G = 0.5

G = 1

G = 2

Parameter

Conditions

Min Typ Max Min Typ Max Min Typ Max Unit

DYNAMIC PERFORMANCE

Bandwidth

Slew Rate

Settling Time to 0.01%

Settling Time to 0.001%

NOISE/DISTORTION

Harmonic Distortion

20

30

15

30

10

30

MHz

V/μs

ns

5 V step on output

550 650

600 750

550 650

600 750

550 650

600 750

ns

f = 1 kHz, V_OUT= 5 V p-p,

R_LOAD= 600 Ω

f = 0.1 Hz to 10 Hz

f = 1 kHz

101

141

112

dB

Voltage Noise¹

2

1.5

38

1

μV p-p

nV/√Hz

52

26

GAIN

Gain Error

0.08

%

Gain Drift

T_A= −40°C to +85°C

1

10

1

10

1

10

ppm/°C

INPUT CHARACTERISTICS

Offset²

450 1500

300 1000

225 750

μV

Average Temperature Drift

Common-Mode Rejection Ratio

T_A= −40°C to +85°C

DC to 1 kHz

3

86

2

92

1.5

98

μV/°C

dB

70

76

80

Power Supply Rejection Ratio

Input Voltage Range³

Common-Mode Resistance⁴

Bias Current

2

10

+5.4

2

10

+5.4

2

10

+5.4

dB

V

kΩ

nA

−5.4

7.5

10

7.5

500

OUTPUT CHARACTERISTICS

Output Swing

−4

+4

−4

+4

−4

+4

V

T_A= −40°C to +85°C

Sourcing

Sinking

−3.9

+3.9 −3.9

+3.9

V

mA

Short-Circuit Current Limit

100

60

100

60

100

60

POWER SUPPLY

Supply Current (per Amplifier)

2.3

2.5

3

2.3

2.5

3

2.3

2.5

3

mA

T_A= −40°C to +85°C

¹Includes amplifier voltage and current noise, as well as noise of internal resistors.

²Includes input bias and offset errors.

³At voltages beyond the rails, internal ESD diodes begin to turn on. In some configurations, the input voltage range may be limited by the internal op amp (see the

Input Voltage Range section for details).

⁴Internal resistors are trimmed to be ratio matched but have 20% absolute accuracy. Common-mode resistance was calculated with both inputs in parallel. Common-

mode impedance at only one input is 2× the resistance listed.

Rev. 0 | Page 4 of 20

AD8270

ABSOLUTE MAXIMUM RATINGS

Table 4.

Parameter

MAXIMUM POWER DISSIPATION

Rating

The maximum safe power dissipation for the AD8270 is limited

by the associated rise in junction temperature (T_J) on the die. At

approximately 130°C, which is the glass transition temperature,

the plastic changes its properties. Even temporarily exceeding

this temperature limit may change the stresses that the package

exerts on the die, permanently shifting the parametric performance

of the amplifiers. Exceeding a temperature of 130°C for an

extended period of time can result in a loss of functionality.

Supply Voltage

Output Short-Circuit Current

18 V

See derating

curve in Figure 2

V_S

−65°C to +130°C

−40°C to +85°C

130°C

1 kV

Input Voltage Range

Storage Temperature Range

Specified Temperature Range

Package Glass Transition Temperature (T_G)

ESD (Human Body Model)

ESD (Charge Device Model)

ESD (Machine Model)

The AD8270 has built-in, short-circuit protection that limits the

output current to approximately 100 mA (see Figure 19 for

more information). While the short-circuit condition itself does

not damage the part, the heat generated by the condition can

cause the part to exceed its maximum junction temperature,

with corresponding negative effects on reliability.

0.1 kV

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.

3.2

T

MAXIMUM = 130°C

J

2.8

2.4

2.0

1.6

PAD SOLDERED

= 57°C/W

θ

JA

THERMAL RESISTANCE

Table 5. Thermal Resistance

Thermal Pad

1.2

0.8

0.4

0

θ_JA

Unit

PAD NOT SOLDERED

= 96°C/W

θ

JA

16-Lead LFCSP with Thermal Pad

Soldered to Board

16-Lead LFCSP with Thermal Pad

Not Soldered to Board

57

°C/W

96

°C/W

–50

–25

0

25

50

75

100

125

AMBIENT TEMPERATURE (°C)

The θ_JAvalues in Table 5 assume a 4-layer JEDEC standard

board with zero airflow. If the thermal pad is soldered to the

board, it is also assumed it is connected to a plane. θ_JCat the

exposed pad is 9.7°C/W.

Figure 2. Maximum Power Dissipation vs. Ambient Temperature

ESD CAUTION

Rev. 0 | Page 5 of 20

AD8270

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

PIN 1

INDICATOR

12 –IN1B

11 –IN2B

10 +IN2B

–IN1A 1

–IN2A 2

+IN2A 3

+IN1A 4

AD8270

TOP VIEW

(Not to Scale)

9

+IN1B

Figure 3. Pin Configuration

Table 6. Pin Function Descriptions

Pin No.

Mnemonic

Description

1

2

3

4

5

−IN1A

−IN2A

+IN2A

+IN1A

10 kΩ Resistor Connected to Negative Terminal of Op Amp A.

10 kΩ Resistor Connected to Positive Terminal of Op Amp A.

20 kΩ Resistor Connected to Positive Terminal of Op Amp A. Most configurations use this pin as a reference

voltage input.

REF1A

6

7

8

REF2A

REF2B

REF1B

20 kΩ Resistor Connected to Positive Terminal of Op Amp A. Most configurations use this pin as a reference

voltage input.

20 kΩ Resistor Connected to Positive Terminal of Op Amp B. Most configurations use this pin as a reference

voltage input.

20 kΩ Resistor Connected to Positive Terminal of Op Amp B. Most configurations use this pin as a reference

voltage input.

9

+IN1B

+IN2B

−IN2B

−IN1B

−V_S

OUTB

OUTA

+V_S

10 kΩ Resistor Connected to Positive Terminal of Op Amp B.

10 kΩ Resistor Connected to Negative Terminal of Op Amp B.

Negative Supply.

Op Amp B Output.

Op Amp A Output.

Positive Supply.

10

11

12

13

14

15

16

Rev. 0 | Page 6 of 20

AD8270

TYPICAL PERFORMANCE CHARACTERISTICS

V_S= 15 V, T_A= 25°C, difference amplifier configuration, unless otherwise noted.

160

20

N: 1043

MEAN: –0.003

SD: 0.28

(0, +15)

140

120

100

80

15

10

5

(–7.5, +7.5)

(+7.5, +7.5)

0

60

40

20

0

–5

–10

–15

–20

(–7.5, –7.5)

(+7.5, –7.5)

(0, –15)

–0.9

–0.6

–0.3

0

0.3

0.6

0.9

–10

–5

0

5

10

SYSTEM OFFSET VOLTAGE (mV)

OUTPUT VOLTAGE (V)

Figure 4. Typical Distribution of System Offset Voltage, G = 1

Figure 7. Common-Mode Input Voltage vs. Output Voltage,

Gain = 0.5, 15 V Supplies

6

N: 984

MEAN: –1.01

(0, +5)

180

SD: 27

4

(–2.5, +2.5)

(+2.5, +2.5)

(0, +2.5)

150

120

90

60

30

0

2

0

(–1.25, –1.25)

(+1.25, +1.25)

= ±5

V

= ±2.5

V

S

(–1.25, –1.25)

(+1.25, –1.25)

–2

–4

–6

(0, –2.5)

(–2.5, –2.5)

(+2.5, –2.5)

(0, –5)

0

–150

–100

–50

0

50

100

150

–3

–2

–1

1

2

3

CMRR (µV/V)

OUTPUT VOLTAGE (V)

Figure 5. Typical Distribution of CMRR, G = 1

Figure 8. Common-Mode Input Voltage vs. Output Voltage,

Gain = 0.5, 5 V and 2.5 V Supplies

20

400

350

300

N: 1043

MEAN: –0.015

SD: 0.0068

(0, +15)

15

(–14.3, +7.85)

(+14.3, +7.85)

10

5

250

200

150

100

50

0

–5

–10

–15

–20

(–14.3, –7.85)

(+14.3, –7.85)

(0, –15)

0

–0.04

–0.02

0

0.02

0.04

–20

–15

–10

–5

5

10

15

20

GAIN ERROR (%)

OUTPUT VOLTAGE (V)

Figure 6. Typical Distribution of Gain Error, G = 1

Figure 9. Common-Mode Input Voltage vs. Output Voltage,

Gain = 1, 15 V Supplies

Rev. 0 | Page 7 of 20

AD8270

6

140

120

100

80

(0, +5)

GAIN = 2, 0.5

4

2

0

(–4.3, +2.85)

(+4.3, +2.85)

(0, +2.5)

GAIN = 1

(–1.6, +1.7)

(+1.6, +1.7)

= ±5

V

= ±2.5

V

S

60

40

20

(–1.6, –1.7)

(+1.6, –1.7)

–2

–4

–6

(0, –2.5)

(–4.3, +–2.85)

(+4.3, –2.85)

(0, –5)

0

10

–5

–4

–3

–2

–1

1

2

3

4

5

100

1k

10k

100k

1M

OUTPUT VOLTAGE (V)

FREQUENCY (Hz)

Figure 10. Common-Mode Input Voltage vs. Output Voltage,

Gain = 1, 5 V and 2.5 V Supplies

Figure 13. Positive PSRR vs. Frequency

20

140

120

100

80

(0, +15)

GAIN = 2, 0.5

15

(–14.3, +11.4)

(+14.3, +11.4)

10

5

GAIN = 1

0

60

40

20

0

–5

–10

–15

–20

(–14.3, –11.4)

(+14.3, –11.4)

(0, –15)

0

–20

–15

–10

–5

5

10

15

20

10

100

1k

10k

100k

1M

OUTPUT VOLTAGE (V)

FREQUENCY (Hz)

Figure 14. Negative PSRR vs. Frequency

Figure 11. Common-Mode Input Voltage vs. Output Voltage,

Gain = 2, 15 V Supplies

32

6

(0, +5)

V

= ±15V

S

(–4, +4)

(+4, +4)

28

24

20

16

4

2

0

(0, +2.5)

(–1.6, +2.1)

(+1.6, +2.1)

V

= ±2.5

V = ±5

S

12

8

–2

–4

–6

V

= ±5V

S

(–1.6, –2.1)

(+1.6, –2.1)

(0, –2.5)

4

(–4, –4)

–4

(+4, –4)

(0, –5)

0

100

1k

10k

100k

1M

10M

–5

–3

–2

–1

1

2

3

4

5

FREQUENCY (Hz)

OUTPUT VOLTAGE (V)

Figure 12. Common-Mode Input Voltage vs. Output Voltage,

Gain = 2, 5 V and 2.5 V Supplies

Figure 15. Output Voltage Swing vs. Large Signal Frequency Response

Rev. 0 | Page 8 of 20

AD8270

10

5

120

100

80

I

SHORT+

GAIN = 2

60

GAIN = 1

0

40

20

GAIN = 0.5

–5

0

–20

–40

–60

–80

–100

–120

–10

–15

–20

I

SHORT–

–40

–20

0

20

40

60

80

100

120

100

1k

10k

100k

1M

10M

100M

TEMPERATURE (°C)

FREQUENCY (Hz)

Figure 16. Gain vs. Frequency

Figure 19. Short-Circuit Current vs. Temperature

100

90

80

70

60

50

40

30

20

10

0

+V

S

+125°C

GAIN = 2, 0.5

GAIN = 1

+V – 2

S

+85°C

–40°C

+25°C

+V – 4

S

0

+125°C

+85°C

+25°C

–V + 2

S

–V + 4

S

–40°C

–V

S

200

1k

10k

10

100

1k

10k

100k

1M

10M

R

(Ω)

FREQUENCY (Hz)

LOAD

Figure 20. Output Voltage Swing vs. R_LOAD

Figure 17. CMRR vs. Frequency

+V

0

S

–40°C

+25°C

CROSSTALK (G = 1)

–20

–40

–60

+V – 3

S

+V – 6

S

+125°C

+85°C

0

–80

–100

–120

+125°C

+85°C

+25°C

–V + 6

S

–V + 3

S

–40°C

–V

–140

S

0

20

40

60

80

100

10

100

1k

10k

100k

FREQUENCY (Hz)

CURRENT (mA)

Figure 18. Channel Separation vs. Frequency

Figure 21. Output Voltage Swing vs. Current (I_OUT)

Rev. 0 | Page 9 of 20

AD8270

160

V

= ±15V

0pF

S

140

120

100

80

100pF

V

= ±10V

S

18pF

V

= ±5V

S

V

= ±2.5V

S

60

40

20

0

V

= ±18V

S

V

= ±15V

50

S

1µs/DIV

0

10

20

30

40

60

70

80

90

100

CAPACITIVE LOAD (pF)

Figure 22. Small Signal Step Response, Gain = 0.5

Figure 25. Small Signal Overshoot with Capacitive Load, Gain = 0.5

80

70

V

= ±15V

0pF

S

220pF

33pF

60

50

40

V

= ±10V

S

V

= ±5V

S

V

= ±2.5V

S

30

20

10

0

V

= ±18V

S

V

= ±15V

S

1µs/DIV

0

50

100

150

200

CAPACITIVE LOAD (pF)

Figure 26. Small Signal Overshoot with Capacitive Load, Gain = 1

Figure 23. Small Signal Step Response, Gain = 1

80

V

= ±15V

S

70

60

50

470pF

100pF

0pF

V

= ±10V

S

40

30

20

10

0

V

= ±5V

S

V

= ±2.5V

S

V

= ±18V

350

S

V

= ±15V

S

1µs/DIV

0

50

100

150

200

250 300

400

450

CAPACITIVE LOAD (pF)

Figure 24. Small Signal Step Response, Gain = 2

Figure 27. Small Signal Overshoot with Capacitive Load, Gain = 2

Rev. 0 | Page 10 of 20

AD8270

45

40

35

30

25

20

15

10

5

V

= ±15V

= ±5V

S

IN

+SR

–SR

0

1µs/DIV

–45–35–25–15 –5

5

15 25 35 45 55 65 75 85 95 105 115 125

TEMPERATURE (°C)

Figure 28. Large Signal Pulse Response Gain = 0.5

Figure 31. Output Slew Rate vs. Temperature

1k

V

= ±15V

= ±5V

S

IN

GAIN = 2

100

GAIN = 1

GAIN = 0.5

10

1µs/DIV

1

10

100

1k

10k

100k

FREQUENCY (Hz)

Figure 29. Large Signal Pulse Response Gain = 1

Figure 32. Voltage Noise Spectral Density vs. Frequency, Referred to Output

V

= ±15V

S

GAIN = 2

= ±5V

IN

GAIN = 1

GAIN = 1/2

1µV/DIV

1s/DIV

1µs/DIV

Figure 30. Large Signal Pulse Response, Gain = 2

Figure 33. 0.1 Hz to 10 Hz Voltage Noise, Referred to Output

Rev. 0 | Page 11 of 20

AD8270

N: 1043

MEAN: 4.6

SD: 134.5

210

180

150

120

90

60

30

0

–600

–400

–200

0

200

400

600

0

1

2

3

4

5

6

7

8

9

10

V

(µV)

TIME (s)

OSI

Figure 34. Typical Distribution of Op Amp Voltage Offset

Figure 37. Change in Op Amp Offset Voltage vs. Warm-Up Time

100

N: 1043

MEAN: 321.6

SD: 6.9

80

60

40

20

0

50pA/DIV

1s/DIV

310

315

320

325

330

335

340

I

(nA)

BIAS

Figure 38. 0.1 Hz to 10 Hz Current Noise of Internal Op Amp

Figure 35. Typical Distribution of Op Amp Bias Current

10

160

140

120

100

N: 1043

MEAN: 0.31

SD: 2.59

1

80

60

40

20

0

0.1

–9

–6

–3

0

3

6

9

12

1

10

100

1k

10k

100k

I

(nA)

OFFSET

FREQUENCY (Hz)

Figure 39. Current Noise Spectral Density of Internal Op Amp

Figure 36. Typical Distribution of Op Amp Offset Current

Rev. 0 | Page 12 of 20

AD8270

THEORY OF OPERATION

Size

The AD8270 fits two op amps and 14 resistors in a 4 mm ×

4 mm package.

DRIVING THE AD8270

10kΩ

The AD8270 is easy to drive, with all configurations presenting

at least several kilohms (kΩ) of input resistance. The AD8270

should be driven with a low impedance source: for example,

another amplifier. The gain accuracy and common-mode rejection

of the AD8270 depend on the matching of its resistors. Even

source resistance of a few ohms can have a substantial effect on

these specifications.

–IN1A 1

–IN2A 2

+IN2A 3

+IN1A 4

12 –IN1B

11 –IN2B

10 +IN2B

_

+

_

+

10kΩ

AD8270

9

+IN1B

20kΩ 20kΩ

PACKAGE CONSIDERATIONS

The AD8270 is packaged in a 4 mm × 4 mm LFCSP. Beware of

blindly copying the footprint from another 4 mm × 4 mm LFCSP

part; it may not have the same thermal pad size and leads. Refer

to the Outline Dimensions section to verify that the PCB symbol

has the correct dimensions.

Figure 40. Functional Block Diagram

CIRCUIT INFORMATION

The 4 mm × 4 mm LFCSP of the AD8270 comes with a thermal

pad. This pad is connected internally to −V_S. Connecting to this

pad is not necessary for electrical performance; the pad can be

left unconnected or can be connected to the negative supply rail.

The AD8270 has two channels, each consisting of a high precision,

low distortion op amp and seven trimmed resistors. These resis-

tors can be connected to make a wide variety of amplifier

configurations: difference, noninverting, inverting, and more.

The resistors on the chip can be connected in parallel for a wider

range of options. Using the on-chip resistors of the AD8270

provides the designer several advantages over a discrete design.

Connecting the pad to the negative supply rail is recommended

in high vibration applications or when good heat dissipation is

required (for example, with high ambient temperatures or when

driving heavy loads). For best heat dissipation performance, the

negative supply rail should be a plane in the board. See the

Absolute Maximum Ratings section for thermal coefficients

with and without the pad soldered.

DC Performance

Much of the dc performance of op amp circuits depends on the

accuracy of the surrounding resistors. The resistors on the AD8270

are laid out to be tightly matched. The resistors of each part are

laser trimmed and tested for their matching accuracy. Because

of this trimming and testing, the AD8270 can guarantee high

accuracy for specifications such as gain drift, common-mode

rejection, and gain error.

Space between the leads and thermal pad should be as wide as

possible to minimize the risk of contaminants affecting perform-

ance. A thorough washing of the board is recommended after the

soldering process, especially if high accuracy performance is

required at high temperatures.

AC Performance

POWER SUPPLIES

Because feature size is much smaller in an integrated circuit than

on a PCB board, the corresponding parasitics are smaller, as well.

The smaller feature size helps the ac performance of the AD8270.

For example, the positive and negative input terminals of the

AD8270 op amp are not pinned out intentionally. By not

connecting these nodes to the traces on the PCB board, the

capacitance remains low, resulting in both improved loop

stability and common-mode rejection over frequency.

A stable dc voltage should be used to power the AD8270. Noise

on the supply pins can adversely affect performance. A bypass

capacitor of 0.1 μF should be placed between each supply pin

and ground, as close as possible to each supply pin. A tantalum

capacitor of 10 μF should also be used between each supply and

ground. It can be farther away from the supply pins and, typically,

it can be shared by other precision integrated circuits.

Production Costs

The AD8270 is specified at 15 V and 5 V, but it can be used with

unbalanced supplies, as well. For example, −V_S= 0 V, +V_S= 20 V.

The difference between the two supplies must be kept below 36 V.

Because one part, rather than several, is placed on the PCB

board, the board can be built more quickly.

Rev. 0 | Page 13 of 20

AD8270

The internal op amp voltage range may be relevant in the

following applications, and calculating the voltage at the

internal op amp is advised.

INPUT VOLTAGE RANGE

The AD8270 has a true rail-to-rail input range for the majority

of applications. Because most AD8270 configurations divide down

the voltage before they reach the internal op amp, the op amp sees

only a fraction of the input voltage. Figure 41 shows an example

of how the voltage division works in the difference amplifier

configuration.

•

Difference amplifier configurations using supply voltages

of less than 4.5 V

Difference amplifier configurations with a reference

voltage near the rail

R2

R1 + R2

Single-ended amplifier configurations

(V

)

+IN

R4

For correct operation, the input voltages at the internal op amp

must stay within 1.5 V of either supply rail.

R3

R1

Voltages beyond the supply rails should not be applied to the

part. The part contains ESD diodes at the input pins, which

conduct if voltages beyond the rails are applied. Currents greater

than 5 mA can damage these diodes and the part. For a similar

part that can operate with voltages beyond the rails, see the

AD8273 data sheet.

R2

R1 + R2

(V

)

+IN

Figure 41. Voltage Division in the Difference Amplifier Configuration

Rev. 0 | Page 14 of 20

AD8270

APPLICATIONS INFORMATION

DIFFERENCE AMPLIFIER CONFIGURATIONS

SINGLE-ENDED CONFIGURATIONS

The AD8270 can be configured for a wide variety of single-

ended configurations with gains ranging from −2 to +3.

Table 8 shows a subset of the possible configurations.

The AD8270 can be placed in difference amplifier configurations

with gains of 0.5, 1, and 2. Figure 42 through Figure 44 show the

difference amplifier configurations, referenced to ground. The

AD8270 can also be referred to a combination of reference voltages.

For example, the reference could be set at 2.5 V, using just 5 V

and GND. Some of the possible configurations are shown in

Figure 45 through Figure 47.

Many signal gains have more than one configuration choice,

which allows freedom in choosing the op amp closed-loop gain.

In general, for designs that need to be stable with a large capacitive

load on the output, choose a configuration with high loop gain.

Otherwise, choose a configuration with low loop gain, because

these configurations typically have lower noise, lower offset,

and higher bandwidth.

The layout for Channel A is shown in Figure 42 through Figure 47.

The layout for Channel B is symmetrical. Table 7 shows the pin

connections for Channel A and Channel B.

16

15

16

15

5kΩ

10kΩ

1

2

3

4

1

2

3

4

10kΩ

–IN

+IN

–IN

+IN

–IN

+IN

–IN

+IN

=

10kΩ

5kΩ

+V + –V

5kΩ

GND

20kΩ 20kΩ

5

6

5

6

S

2

GND

–V

+V

S

Figure 42. Gain = 0.5 Difference Amplifier, Referenced to Ground

Figure 45. Gain = 0.5 Difference Amplifier, Referenced to Midsupply

16

15

16

15

10kΩ

1

2

3

4

1

2

3

4

–IN

NC

+IN

–IN

NC

+IN

10kΩ

–IN

+IN

–IN

+IN

=

10kΩ

GND

10kΩ

+V + –V

20kΩ 20kΩ

5

6

5

6

S

2

–V +V

S

GND

S

NC = NO CONNECT

Figure 43. Gain = 1 Difference Amplifier, Referenced to Ground

Figure 46. Gain = 1 Difference Amplifier, Referenced to Midsupply

16

15

16

15

10kΩ

1

2

3

4

1

2

3

4

5kΩ

–IN

+IN

–IN

+IN

–IN

+IN

–IN

+IN

=

10kΩ

20kΩ 20kΩ

10kΩ

GND

20kΩ 20kΩ

10kΩ

+V + –V

5

6

5

6

S

2

–V +V

S

GND

S

Figure 47. Gain = 2 Difference Amplifier, Referenced to Midsupply

Figure 44. Gain = 2 Difference Amplifier, Referenced to Ground

Table 7. Pin Connections for Difference Amplifier Configurations

Channel A

Channel B

Gain and Reference

Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 6 Pin 12 Pin 11 Pin 10 Pin 9 Pin 8 Pin 7

Gain of 0.5, Referenced to Ground

OUT

−IN

NC

+IN

NC

GND

−V_S

+IN

GND

+V_S

GND

+V_S

OUT

−IN

NC

+IN

NC

GND GND GND

Gain of 0.5, Referenced to Midsupply OUT

−V_S

+IN

+V_S

GND GND

−V_S+V_S

GND GND

−V_S+V_S

+V_S

Gain of 1, Referenced to Ground

Gain of 1, Referenced to Midsupply

Gain of 2, Referenced to Ground

Gain of 2, Referenced to Midsupply

−IN

GND

−V_S

GND

+V_S

NC

−IN

+IN

GND

−V_S

GND

+V_S

−IN

+IN

Rev. 0 | Page 15 of 20

AD8270

Table 8. Selected Single-Ended Configurations

Electrical Performance

Pin Connections

20 kΩ +

Pin 5

GND

NC

GND

IN

NC

GND

NC

GND

IN

GND

NC

GND

NC

GND

NC

GND

NC

GND

IN

NC

IN

Op Amp

Closed-Loop Gain

Input

Resistance

10 kΩ −

Pin 1

10 kΩ −

Pin 2

10 kΩ +

Pin 4

20 kΩ +

Pin 6

Signal Gain

−2

−1.5

−1.4

−1.25

−1

−0.8

−0.667

−0.6

Pin 3

GND

IN

GND

IN

GND

IN

NC

GND

IN

GND

IN

GND

IN

NC

IN

3

2

5 kΩ

4.8 kΩ

5 kΩ

5.333 kΩ

5 kΩ

5.556 kΩ

8 kΩ

8.333 kΩ

8.889 kΩ

7.5 kΩ

IN

NC

IN

NC

GND

NC

GND

NC

GND

IN

GND

NC

GND

NC

GND

NC

GND

IN

GND

NC

GND

IN

GND

IN

NC

IN

GND

IN

GND

IN

GND

IN

GND

IN

GND

IN

GND

IN

GND

IN

GND

IN

GND

IN

GND

IN

−0.5

2

IN

−0.333

−0.25

−0.2

−0.125

+0.1

+0.2

+0.25

+0.3

+0.333

+0.375

+0.4

+0.5

1.5

2

1.5

2

1.5

2

3

1.5

3

1.5

2

1.5

3

1.5

2

1.5

3

1.5

3

1.5

2

3

1.5

2

8 kΩ

OUT

IN

8.333 kΩ

8.889 kΩ

8.333 kΩ

10 kΩ

24 kΩ

25 kΩ

24 kΩ

26.67 kΩ

25 kΩ

24 kΩ

15 kΩ

OUT

GND

OUT

GND

OUT

GND

OUT

GND

OUT

GND

OUT

GND

OUT

IN

OUT

GND

OUT

GND

OUT

GND

+0.6

25 kΩ

16.67 kΩ

16 kΩ

+0.625

+0.667

+0.7

+0.75

+0.8

+0.9

+1

+1.125

+1.2

+1.25

+1.333

+1.5

+1.6

+1.667

+1.8

+2

15 kΩ

NC

IN

16.67 kΩ

26.67 kΩ

13.33 kΩ

16.67 kΩ

15 kΩ

>1 GΩ

26.67 kΩ

16.67 kΩ

25 kΩ

24 kΩ

15 kΩ

13.33 kΩ

>1 GΩ

25 kΩ

NC

GND

NC

GND

IN

GND

NC

GND

IN

NC

IN

GND

NC

GND

NC

GND

NC

GND

IN

GND

IN

GND

IN

NC

IN

GND

IN

NC

IN

NC

IN

NC

IN

GND

IN

2

3

2

3

24 kΩ

16.67 kΩ

>1 GΩ

26.67 kΩ

25 kΩ

24 kΩ

>1 GΩ

IN

+2.25

+2.4

+2.5

GND

IN

+3

IN

Rev. 0 | Page 16 of 20

AD8270

+OUT –OUT

The AD8270 Specifications section and Typical Performance

Characteristics section show the performance of the part primarily

when it is in the difference amplifier configuration. To get a good

estimate of the performance of the part in a single-ended

configuration, refer to the difference amplifier configuration

with the corresponding closed-loop gain (see Table 9).

16

15

14

13

V

– V

–IN

= V

– V

–OUT

+IN

+OUT

+ V

–OUT

= V

OCM

+OUT

10kΩ

1

2

3

4

12

11

_

+

–IN

+IN

–IN

+IN

–IN

+OUT

10kΩ

=

V

OCM

10

9

+

–OUT

AD8270

Table 9. Closed-Loop Gain of the Difference Amplifiers

20kΩ 20kΩ

5

6

7

8

Difference Amplifier Gain

Closed-Loop Gain

OCM

0.5

1

2

1.5

2

3

OCM

Figure 48. Differential Output, G = 1, Common-Mode Output Voltage

Set with Reference Voltage

Gain of 1 Configuration

+OUT –OUT

The AD8270 is designed to be stable for loop gains of 1.5 and

greater. Because a typical voltage follower configuration has

a loop gain of 1, it may be unstable. Several stable G = 1 configu-

rations are listed in Table 8.

16

15

14

13

V

– V

–IN

= V

– V

+IN

+OUT –OUT

V

+ V

B

A

+ V

=

+OUT

–OUT

10kΩ

2

1

2

3

4

12

11

_

+

–IN

+IN

A

+IN

–IN

A

+IN

–IN

+OUT

10kΩ

=

V

OCM

10

9

+

DIFFERENTIAL OUTPUT

–OUT

AD8270

The AD8270 can easily be configured for differential output.

Figure 48 shows the configuration for a G = 1 differential output

amplifier. The OCM node in the figure sets the common-mode

output voltage. Figure 49 shows the configuration for a G = 1

differential output amplifier, where the average of two voltages

sets the common-mode output voltage. For example, this

configuration can be used to set the common mode at 2.5 V,

using just a 5 V reference and GND.

20kΩ 20kΩ

5

6

7

8

V

+ V

B

2

A

B

Figure 49. Differential Output, G = 1, Common-Mode Output Voltage

Set as the Average of Two Voltages

Note that these two configurations are based on the G = 0.5

difference amplifier configurations shown in Figure 42 and

Figure 45. A similar technique can be used to create differential

output with a gain of 2 or 4, using the G = 1 and G = 2 difference

amplifier configurations, respectively.

Rev. 0 | Page 17 of 20

AD8270

To reduce the peaking, use a resistor between the AD8270 and the

cable. Because cable capacitance and desired output response vary

widely, this resistor is best determined empirically. A good starting

point is 20 Ω.

DRIVING AN ADC

The AD270 high slew rate and drive capability, combined with

its dc accuracy, make it a good ADC driver. The AD8270 can

drive both single-ended and differential input ADCs. Many

converters require the output to be buffered with a small value

resistor combined with a high quality ceramic capacitor. See the

converter data sheet for more details. Figure 51 shows the AD8270

in differential configuration, driving the AD7688 ADC. The

AD8270 divides down the 5 V reference voltage from the ADR435,

so that the common-mode output voltage is 2.5 V, which is

precisely where the AD7688 needs it.

AD8270

(DIFF OUT)

DRIVING CABLING

AD8270

(SINGLE OUT)

All cables have a certain capacitance per unit length, which varies

widely with cable type. The capacitive load from the cable may

cause peaking or instability in output response, especially when the

AD8270 is operating in a gain of 0.5.

Figure 50. Driving Cabling

+12V –12V

16

13

NOTE:

10kΩ

POWER SUPPLY DECOUPLING

NOT SHOWN.

1

10kΩ

2

3

4

5

6

7

–IN

+IN

33Ω

15

3

4

+IN

AD7688

10kΩ

2.7nF

COG

10kΩ

20kΩ

33Ω

REF

1

–IN

2.7nF

COG

20kΩ

AD8270

5V_REF

0.1µF

+12V

20kΩ

10kΩ

8

9

2

V

IN

V

5

5V_REF

OUT

10

11

–IN

+IN

10µF

ADR435

14

12

GND

4

10kΩ

Figure 51. Driving an ADC

Rev. 0 | Page 18 of 20

AD8270

OUTLINE DIMENSIONS

4.00

BSC SQ

0.60 MAX

0.65 BSC

PIN 1

INDICATOR

13

16

1

12

9

PIN 1

INDICATOR

2.50

2.35 SQ

2.20

TOP

VIEW

EXPOSED

3.75

BSC SQ

PAD

(BOTTOM VIEW)

0.50

0.40

0.30

4

8

5

0.25 MIN

1.95 BSC

0.80 MAX

0.65 TYP

12° MAX

0.05 MAX

0.02 NOM

1.00

0.85

0.80

0.35

0.30

0.25

0.20 REF

COPLANARITY

0.08

SEATING

PLANE

COMPLIANT TO JEDEC STANDARDS MO-220-VGGC

Figure 52. 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ]

4 mm × 4 mm Body, Very Thin Quad

(CP-16-10)

Dimensions are shown in millimeters

ORDERING GUIDE

Model

AD8270ACPZ-R7¹

AD8270ACPZ-RL¹

AD8270ACPZ-WP¹

Temperature Range

−40°C to +85°C

Package Description

16-Lead LFCSP_VQ

Package Option

CP-16-10

¹Z = RoHS Compliant Part.

Rev. 0 | Page 19 of 20

AD8270

NOTES

registered trademarks are the property of their respective owners.

D06979-0-1/08(0)

Rev. 0 | Page 20 of 20


型号：	AD8270ACPZ-R7
厂家：	ADI
描述：	Precision Dual-Channel, Difference Amplifier 精密双通道差分放大器放大器
文件：	总20页 (文件大小：606K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

AD8270ACPZ-R7 [ADI]

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