AD8270ACPZ-WP [ADI]
Precision Dual-Channel, Difference Amplifier; 精密双通道差分放大器型号: | AD8270ACPZ-WP |
厂家: | ADI |
描述: | Precision Dual-Channel, Difference Amplifier |
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 |
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
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
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
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
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
©2008 Analog Devices, Inc. All rights reserved.
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
VS = 15 V, VREF = 0 V, TA = 25°C, RLOAD = 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
10 V step on output
700 800
750 900
700 800
750 900
700 800
750 900
ns
f = 1 kHz, VOUT = 10 V p-p,
RLOAD = 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
0.08
0.08
%
Gain Drift
TA = −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 TA = −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
+15.4 −15.4
7.5
10
7.5
500
500
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
V
mA
mA
TA = −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
mA
TA = −40°C to +85°C
1 Includes amplifier voltage and current noise, as well as noise of internal resistors.
2 Includes input bias and offset errors.
3 At 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).
4 Internal 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
VS = 5 V, VREF = 0 V, TA = 25°C, RLOAD = 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
5 V step on output
550 650
600 750
550 650
600 750
550 650
600 750
ns
f = 1 kHz, VOUT = 5 V p-p,
RLOAD = 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
0.08
0.08
%
Gain Drift
TA = −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
TA = −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
−5.4
−5.4
7.5
10
7.5
500
500
500
OUTPUT CHARACTERISTICS
Output Swing
−4
+4
−4
+4
−4
+4
V
TA = −40°C to +85°C
Sourcing
Sinking
−3.9
+3.9 −3.9
+3.9 −3.9
+3.9
V
mA
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
mA
TA = −40°C to +85°C
1 Includes amplifier voltage and current noise, as well as noise of internal resistors.
2 Includes input bias and offset errors.
3 At 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).
4 Internal 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 (TJ) 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
VS
−65°C to +130°C
−40°C to +85°C
130°C
1 kV
1 kV
Input Voltage Range
Storage Temperature Range
Specified Temperature Range
Package Glass Transition Temperature (TG)
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
θJA
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 θJA values 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. θJC at 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 Negative Terminal of Op Amp A.
10 kΩ Resistor Connected to Positive 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
−VS
OUTB
OUTA
+VS
10 kΩ Resistor Connected to Positive Terminal of Op Amp B.
10 kΩ Resistor Connected to Positive Terminal of Op Amp B.
10 kΩ Resistor Connected to Negative 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
VS = 15 V, TA = 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
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
–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
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
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
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
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. RLOAD
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 (IOUT)
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
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
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
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
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
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
10kΩ
AD8270
9
+IN1B
20kΩ 20kΩ
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 −VS. 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, −VS = 0 V, +VS = 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
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
5kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
1
2
3
4
1
2
3
4
10kΩ
10kΩ
10kΩ
10kΩ
–IN
+IN
–IN
+IN
–IN
+IN
–IN
+IN
=
=
10kΩ
10kΩ
10kΩ
10kΩ
5kΩ
+V + –V
5kΩ
GND
20kΩ 20kΩ
20kΩ 20kΩ
5
6
5
6
S
S
2
GND
–V
+V
S
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
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
1
2
3
4
1
2
3
4
–IN
NC
NC
+IN
–IN
NC
NC
+IN
10kΩ
10kΩ
10kΩ
10kΩ
–IN
+IN
–IN
+IN
=
=
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
GND
10kΩ
+V + –V
20kΩ 20kΩ
20kΩ 20kΩ
5
6
5
6
S
S
2
–V +V
S
GND
S
NC = NO CONNECT
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
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
1
2
3
4
1
2
3
4
5kΩ
5kΩ
5kΩ
5kΩ
–IN
+IN
–IN
+IN
–IN
+IN
–IN
+IN
=
=
10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ
10kΩ
GND
20kΩ 20kΩ
10kΩ
+V + –V
5
6
5
6
S
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
−IN
NC
+IN
+IN
NC
GND
−VS
+IN
+IN
+IN
+IN
GND
+VS
GND
+VS
OUT
OUT
−IN
−IN
−IN
−IN
−IN
−IN
NC
+IN
+IN
NC
GND GND GND
Gain of 0.5, Referenced to Midsupply OUT
−VS
+IN
+IN
+IN
+IN
+VS
GND GND
−VS +VS
GND GND
−VS +VS
+VS
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
−IN
−IN
−IN
GND
−VS
GND
+VS
NC
NC
NC
NC
−IN
−IN
+IN
+IN
GND
−VS
GND
+VS
−IN
−IN
+IN
+IN
Rev. 0 | Page 15 of 20
AD8270
Table 8. Selected Single-Ended Configurations
Electrical Performance
Pin Connections
20 kΩ +
Pin 5
GND
GND
NC
GND
IN
NC
GND
NC
GND
IN
GND
NC
GND
NC
NC
GND
NC
GND
GND
NC
GND
IN
NC
NC
IN
IN
Op Amp
Closed-Loop Gain
Input
Resistance
10 kΩ −
Pin 1
10 kΩ −
Pin 2
10 kΩ +
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
GND
GND
GND
GND
IN
GND
GND
GND
GND
GND
GND
GND
IN
GND
GND
GND
GND
GND
GND
GND
GND
GND
IN
NC
GND
IN
GND
GND
IN
GND
IN
IN
IN
NC
IN
3
3
3
3
3
3
2
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
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
NC
NC
NC
NC
IN
IN
IN
IN
NC
GND
GND
NC
GND
NC
GND
GND
GND
GND
IN
GND
GND
GND
NC
GND
GND
GND
GND
NC
GND
GND
GND
NC
GND
IN
GND
GND
GND
NC
GND
GND
GND
GND
GND
IN
GND
IN
NC
IN
GND
IN
IN
IN
IN
IN
GND
IN
IN
IN
IN
IN
IN
IN
IN
GND
IN
IN
IN
IN
GND
IN
IN
IN
IN
IN
IN
IN
GND
IN
IN
IN
IN
IN
IN
IN
IN
IN
GND
GND
IN
GND
IN
IN
GND
IN
GND
IN
IN
GND
GND
GND
GND
GND
IN
−0.5
2
2
IN
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
+0.5
1.5
1.5
1.5
1.5
2
1.5
1.5
2
1.5
2
3
1.5
3
1.5
1.5
2
1.5
3
1.5
2
1.5
1.5
1.5
3
1.5
3
1.5
1.5
2
3
1.5
2
8 kΩ
OUT
OUT
OUT
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
OUT
GND
OUT
GND
GND
OUT
GND
OUT
OUT
GND
OUT
GND
OUT
GND
OUT
OUT
OUT
IN
OUT
GND
OUT
OUT
GND
GND
OUT
GND
GND
GND
GND
GND
GND
GND
GND
+0.6
+0.6
25 kΩ
16.67 kΩ
16 kΩ
+0.625
+0.667
+0.7
+0.75
+0.75
+0.8
+0.9
+1
+1
+1
+1.125
+1.2
+1.2
+1.25
+1.333
+1.5
+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
16.67 kΩ
15 kΩ
>1 GΩ
>1 GΩ
26.67 kΩ
16.67 kΩ
25 kΩ
24 kΩ
15 kΩ
13.33 kΩ
>1 GΩ
25 kΩ
NC
GND
GND
NC
GND
GND
IN
GND
GND
NC
NC
GND
IN
IN
IN
NC
NC
IN
GND
GND
GND
GND
NC
GND
GND
NC
NC
GND
NC
GND
GND
GND
GND
IN
IN
IN
GND
IN
IN
IN
GND
IN
NC
IN
GND
GND
IN
NC
IN
NC
IN
IN
NC
IN
GND
GND
IN
2
3
2
3
3
3
3
24 kΩ
16.67 kΩ
>1 GΩ
26.67 kΩ
25 kΩ
24 kΩ
>1 GΩ
IN
IN
IN
IN
IN
+2.25
+2.4
+2.5
GND
GND
GND
IN
IN
IN
IN
IN
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
– V
–IN
= V
– V
–OUT
+IN
+OUT
+ V
–OUT
= V
OCM
+OUT
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
1
2
3
4
12
11
_
_
+
–IN
+IN
+IN
–IN
+IN
–IN
+OUT
10kΩ
10kΩ
=
V
OCM
10
9
+
–OUT
AD8270
Table 9. Closed-Loop Gain of the Difference Amplifiers
20kΩ 20kΩ
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
– V
–IN
= V
– V
+IN
+OUT –OUT
V
+ V
B
A
+ V
=
+OUT
–OUT
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
2
1
2
3
4
12
11
_
_
+
–IN
+IN
A
+IN
–IN
A
+IN
–IN
+OUT
10kΩ
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
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
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
20kΩ
AD8270
5V_REF
0.1µF
0.1µF
+12V
20kΩ
10kΩ
10kΩ
10kΩ
8
9
2
V
IN
V
5
5V_REF
OUT
10
11
–IN
+IN
10µF
ADR435
14
12
GND
4
10kΩ
10kΩ
Figure 51. Driving an ADC
Rev. 0 | Page 18 of 20
AD8270
OUTLINE DIMENSIONS
4.00
BSC SQ
0.60 MAX
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
−40°C to +85°C
−40°C to +85°C
Package Description
16-Lead LFCSP_VQ
16-Lead LFCSP_VQ
16-Lead LFCSP_VQ
Package Option
CP-16-10
CP-16-10
CP-16-10
1 Z = RoHS Compliant Part.
Rev. 0 | Page 19 of 20
AD8270
NOTES
©2008 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D06979-0-1/08(0)
Rev. 0 | Page 20 of 20
相关型号:
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INSTRUMENTATION AMPLIFIER, 1500 uV OFFSET-MAX, PDSO10, ROHS COMPLIANT, MO-187BA, MSOP-10
ROCHESTER
AD8271BRMZ
INSTRUMENTATION AMPLIFIER, 1000 uV OFFSET-MAX, PDSO10, ROHS COMPLIANT, MO-187BA, MSOP-10
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