AD8270: Precision, Dual-Channel Difference Amplifier Data Sheet (Rev. 0) PDF

Precision Dual-Channel,
Difference Amplifier
AD8270
Instrumentation amplifier building blocks
Level translators
Automatic test equipment
High performance audio
Sine/Cosine encoders
13 –VS
14 OUTB
_
_
+
+
10kΩ
20kΩ
20kΩ
10kΩ
10kΩ
10kΩ
AD8270
20kΩ
APPLICATIONS
10kΩ
12 –IN1B
11 –IN2B
10 +IN2B
9 +IN1B
20kΩ
06979-001
+IN1A 4
10kΩ
10kΩ
REF1B 8
+IN2A 3
10kΩ
10kΩ
REF2B 7
–IN2A 2
10kΩ
REF2A 6
–IN1A 1
15 OUTA
FUNCTIONAL BLOCK DIAGRAM
REF1A 5
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
High accuracy dc performance
0.08% maximum gain error
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
16 +VS
FEATURES
Figure 1.
GENERAL DESCRIPTION
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 singleended configurations, with gains ranging from −2 to +3.
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.
Table 1. Difference Amplifiers by Category
High
Speed
AD8270
AD8273
AMP03
High
Voltage
AD628
AD629
Single-Supply
Unidirectional
AD8202
AD8203
Single-Supply
Bidirectional
AD8205
AD8206
AD8216
The AD8270 operates on both single and dual supplies and
requires only 2.5 mA maximum supply current for each amplifier. 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 registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2008 Analog Devices, Inc. All rights reserved.
AD8270
TABLE OF CONTENTS
Features .............................................................................................. 1
Circuit Information.................................................................... 13
Applications....................................................................................... 1
Driving the AD8270................................................................... 13
General Description ......................................................................... 1
Package Considerations............................................................. 13
Functional Block Diagram .............................................................. 1
Power Supplies............................................................................ 13
Revision History ............................................................................... 2
Input Voltage Range................................................................... 14
Specifications..................................................................................... 3
Applications Information .............................................................. 15
Difference Amplifier Configurations ........................................ 3
Difference Amplifier Configurations ...................................... 15
Absolute Maximum Ratings............................................................ 5
Single-Ended Configurations ................................................... 15
Thermal Resistance ...................................................................... 5
Differential Output .................................................................... 17
Maximum Power Dissipation ..................................................... 5
Driving an ADC ......................................................................... 18
ESD Caution.................................................................................. 5
Driving Cabling .......................................................................... 18
Pin Configuration and Function Descriptions............................. 6
Outline Dimensions ....................................................................... 19
Typical Performance Characteristics ............................................. 7
Ordering Guide .......................................................................... 19
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.
Parameter
DYNAMIC PERFORMANCE
Bandwidth
Slew Rate
Settling Time to 0.01%
Settling Time to 0.001%
NOISE/DISTORTION
Harmonic Distortion
Voltage Noise 1
GAIN
Gain Error
Gain Drift
INPUT CHARACTERISTICS
Offset 2
Average Temperature Drift
Common-Mode Rejection
Ratio
Power Supply Rejection Ratio
Input Voltage Range 3
Common-Mode Resistance 4
Bias Current
OUTPUT CHARACTERISTICS
Output Swing
Short-Circuit Current Limit
Conditions
Min
G = 0.5
Typ Max
20
30
700
750
10 V step on output
10 V step on output
Min
G=1
Typ Max
15
30
700
750
800
900
Min
G=2
Typ Max
10
30
700
750
800
900
800
900
Unit
MHz
V/μs
ns
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
2
52
1.5
38
1
26
μV p-p
nV/√Hz
TA = −40°C to +85°C
1
450
3
86
1500
TA = −40°C to +85°C
DC to 1 kHz
2
10
+15.4
70
−15.4
0.08
10
1
76
300
2
92
1000
2
10
+15.4
−15.4
7.5
POWER SUPPLY
Supply Current
(per Amplifier)
−13.8
−13.7
+13.8
+13.7
100
60
2.3
TA = −40°C to +85°C
80
3
1
%
ppm/°C
225
1.5
98
750
μV
μV/°C
dB
2
10
+15.4
μV/V
V
kΩ
nA
−15.4
7.5
500
−13.8
−13.7
+13.8
+13.7
100
60
2.5
0.08
10
1
10
500
TA = −40°C to +85°C
Sourcing
Sinking
0.08
10
2.3
500
−13.8
−13.7
+13.8
+13.7
V
V
mA
mA
2.5
mA
3
mA
100
60
2.5
3
2.3
Includes amplifier voltage and current noise, as well as noise of internal resistors.
Includes input bias and offset errors.
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. Commonmode impedance at only one input is 2× the resistance listed.
2
3
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.
Parameter
DYNAMIC PERFORMANCE
Bandwidth
Slew Rate
Settling Time to 0.01%
Settling Time to 0.001%
NOISE/DISTORTION
Harmonic Distortion
Voltage Noise 1
GAIN
Gain Error
Gain Drift
INPUT CHARACTERISTICS
Offset 2
Average Temperature Drift
Common-Mode Rejection Ratio
Conditions
G = 0.5
Typ Max
20
30
550
600
5 V step on output
5 V step on output
Min
G=1
Typ Max
15
30
550
600
650
750
Min
650
750
G=2
Typ Max
Unit
10
30
550
600
MHz
V/μs
ns
ns
650
750
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
2
52
1.5
38
1
26
μV p-p
nV/√Hz
TA = −40°C to +85°C
1
450
3
86
1500
TA = −40°C to +85°C
DC to 1 kHz
2
10
+5.4
Power Supply Rejection Ratio
Input Voltage Range 3
Common-Mode Resistance 4
Bias Current
OUTPUT CHARACTERISTICS
Output Swing
Short-Circuit Current Limit
Min
70
−5.4
0.08
10
1
76
300
2
92
1000
2
10
+5.4
−5.4
7.5
POWER SUPPLY
Supply Current (per Amplifier)
−4
−3.9
+4
+3.9
100
60
2.3
TA = −40°C to +85°C
1
80
%
ppm/°C
225
1.5
98
750
μV
μV/°C
dB
2
10
+5.4
dB
V
kΩ
nA
−5.4
7.5
500
−4
−3.9
+4
+3.9
100
60
2.5
3
0.08
10
1
10
500
TA = −40°C to +85°C
Sourcing
Sinking
0.08
10
2.3
500
−4
−3.9
+4
+3.9
V
V
mA
mA
2.5
3
mA
mA
100
60
2.5
3
2.3
Includes amplifier voltage and current noise, as well as noise of internal resistors.
Includes input bias and offset errors.
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. Commonmode impedance at only one input is 2× the resistance listed.
2
3
Rev. 0 | Page 4 of 20
AD8270
ABSOLUTE MAXIMUM RATINGS
Table 4.
MAXIMUM POWER DISSIPATION
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)
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.
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.
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.
3.2
TJ MAXIMUM = 130°C
THERMAL RESISTANCE
Table 5. Thermal Resistance
Thermal Pad
16-Lead LFCSP with Thermal Pad
Soldered to Board
16-Lead LFCSP with Thermal Pad
Not Soldered to Board
θJA
57
Unit
°C/W
96
°C/W
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.
2.8
2.4
PAD SOLDERED
θJA = 57°C/W
2.0
1.6
1.2
0.8
PAD NOT SOLDERED
θJA = 96°C/W
0.4
0
–50
–25
0
25
50
75
AMBIENT TEMPERATURE (°C)
100
125
Figure 2. Maximum Power Dissipation vs. Ambient Temperature
ESD CAUTION
Rev. 0 | Page 5 of 20
06979-003
Rating
±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
0.1 kV
MAXIMUM POWER DISSIPATION (W)
Parameter
Supply Voltage
Output Short-Circuit Current
AD8270
11 –IN2B
10 +IN2B
9 +IN1B
06979-002
REF2B 7
12 –IN1B
REF1B 8
TOP VIEW
(Not to Scale)
REF1A 5
+IN1A 4
AD8270
REF2A 6
+IN2A 3
13 –VS
PIN 1
INDICATOR
–IN1A 1
–IN2A 2
14 OUTB
16 +VS
15 OUTA
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Figure 3. Pin Configuration
Table 6. Pin Function Descriptions
Pin No.
1
2
3
4
5
Mnemonic
−IN1A
−IN2A
+IN2A
+IN1A
REF1A
6
REF2A
7
REF2B
8
REF1B
9
10
11
12
13
14
15
16
+IN1B
+IN2B
−IN2B
−IN1B
−VS
OUTB
OUTA
+VS
Description
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.
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.
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.
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)
COMMON-MODE INPUT VOLTAGE (V)
140
NUMBER OF UNITS
120
100
80
60
40
20
15
10
(–7.5, +7.5)
(+7.5, +7.5)
(–7.5, –7.5)
(+7.5, –7.5)
5
0
–5
–10
–15
–0.3
0
0.3
0.6
SYSTEM OFFSET VOLTAGE (mV)
0.9
Figure 4. Typical Distribution of System Offset Voltage, G = 1
6
COMMON-MODE INPUT VOLTAGE (V)
120
90
60
30
–50
0
CMRR (µV/V)
50
100
150
2
(+2.5, +2.5)
(0, +2.5)
(–1.25, –1.25)
(+1.25, +1.25)
VS = ±2.5
VS = ±5
0
(–1.25, –1.25)
–2
–4
(+1.25, –1.25)
(0, –2.5)
(–2.5, –2.5)
(+2.5, –2.5)
(0, –5)
–2
–1
0
1
OUTPUT VOLTAGE (V)
2
3
COMMON-MODE INPUT VOLTAGE (V)
(0, +15)
300
250
200
150
100
50
15
10
(–14.3, +7.85)
(+14.3, +7.85)
(–14.3, –7.85)
(+14.3, –7.85)
5
0
–5
–10
–15
(0, –15)
0
–0.04
–0.02
0
GAIN ERROR (%)
0.02
0.04
–20
–20
06979-006
NUMBER OF UNITS
(–2.5, +2.5)
20
N: 1043
MEAN: –0.015
SD: 0.0068
350
4
Figure 8. Common-Mode Input Voltage vs. Output Voltage,
Gain = 0.5, ±5 V and ±2.5 V Supplies
Figure 5. Typical Distribution of CMRR, G = 1
400
10
(0, +5)
–6
–3
06979-005
–100
5
–15
–10
–5
0
5
OUTPUT VOLTAGE (V)
10
15
20
Figure 9. Common-Mode Input Voltage vs. Output Voltage,
Gain = 1, ±15 V Supplies
Figure 6. Typical Distribution of Gain Error, G = 1
Rev. 0 | Page 7 of 20
06979-009
NUMBER OF UNITS
150
0
–150
0
OUTPUT VOLTAGE (V)
Figure 7. Common-Mode Input Voltage vs. Output Voltage,
Gain = 0.5, ±15 V Supplies
N: 984
MEAN: –1.01
SD: 27
180
–5
06979-008
–0.6
06979-004
–0.9
–20
–10
06979-007
(0, –15)
0
AD8270
140
(0, +5)
GAIN = 2, 0.5
4 (–4.3, +2.85)
120
(+4.3, +2.85)
(–1.6, +1.7)
(+1.6, +1.7)
VS = ±2.5
VS = ±5
0
(–1.6, –1.7)
–2
(+1.6, –1.7)
(0, –2.5)
–2.85)
–4 (–4.3, +2.85)
(+4.3, –2.85)
–4
–3
–2
–1
0
1
2
OUTPUT VOLTAGE (V)
3
4
5
GAIN = 1
80
60
40
20
(0, –5)
–6
–5
100
0
10
Figure 10. Common-Mode Input Voltage vs. Output Voltage,
Gain = 1, ±5 V and ±2.5 V Supplies
100k
1M
140
(0, +15)
GAIN = 2, 0.5
15
120
(–14.3, +11.4)
(+14.3, +11.4)
10
NEGATIVE PSRR (dB)
COMMON-MODE INPUT VOLTAGE (V)
1k
10k
FREQUENCY (Hz)
Figure 13. Positive PSRR vs. Frequency
20
5
0
–5
–10
100
06979-015
2
POSITIVE PSRR (dB)
(0, +2.5)
06979-010
COMMON-MODE INPUT VOLTAGE (V)
6
(–14.3, –11.4)
100
GAIN = 1
80
60
40
(+14.3, –11.4)
20
–15
–15
–10
–5
0
5
OUTPUT VOLTAGE (V)
10
15
20
0
10
06979-011
100k
1M
32
6
(0, +5)
(–4, +4)
VS = ±15V
(+4, +4)
28
(–1.6, +2.1)
(0, +2.5)
OUTPUT VOLTAGE SWING (V p-p)
4
(+1.6, +2.1)
2
VS = ±2.5
VS = ±5
0
–2
(–1.6, –2.1)
(0, –2.5)
(+1.6, –2.1)
–4
(–4, –4)
(0, –5)
–4
–3
–2
–1
0
1
2
OUTPUT VOLTAGE (V)
3
4
24
20
16
12
8
VS = ±5V
4
(+4, –4)
5
Figure 12. Common-Mode Input Voltage vs. Output Voltage,
Gain = 2, ±5 V and ±2.5 V Supplies
0
100
06979-012
COMMON-MODE INPUT VOLTAGE (V)
1k
10k
FREQUENCY (Hz)
Figure 14. Negative PSRR vs. Frequency
Figure 11. Common-Mode Input Voltage vs. Output Voltage,
Gain = 2, ±15 V Supplies
–6
–5
100
1k
10k
100k
FREQUENCY (Hz)
1M
10M
06979-017
–20
–20
06979-016
(0, –15)
Figure 15. Output Voltage Swing vs. Large Signal Frequency Response
Rev. 0 | Page 8 of 20
AD8270
10
120
GAIN (dB)
SHORT-CIRCUIT CURRENT (mA)
5
GAIN = 1
0
GAIN = 0.5
–5
ISHORT+
100
GAIN = 2
–10
–15
80
60
40
20
0
–20
–40
ISHORT–
–60
–80
1k
10k
100k
1M
FREQUENCY (Hz)
10M
100M
–120
–40
06979-018
GAIN = 1
OUTPUT VOLTAGE SWING (V)
+VS
80
40
60
80
100
60
50
40
30
20
+125°C
+VS – 2
–40°C
+25°C
+85°C
+VS – 4
0
+125°C
+85°C
–VS + 2
+25°C
–VS + 4
10
–40°C
1k
10k
100k
FREQUENCY (Hz)
1M
10M
06979-019
100
–VS
200
1k
RLOAD (Ω)
10k
Figure 20. Output Voltage Swing vs. RLOAD
Figure 17. CMRR vs. Frequency
+VS
0
–40°C
+25°C
CROSSTALK (G = 1)
OUTPUT VOLTAGE SWING (V)
–40
–60
–80
–100
+VS – 3
+VS – 6
+125°C
+85°C
0
+125°C
–VS + 6
+85°C
+25°C
–VS + 3
–120
100
1k
FREQUENCY (Hz)
10k
100k
–VS
06979-013
CHANNEL SEPARATION (dB)
–20
–140
10
120
06979-022
CMRR (dB)
70
0
10
20
Figure 19. Short-Circuit Current vs. Temperature
100
GAIN = 2, 0.5
0
TEMPERATURE (°C)
Figure 16. Gain vs. Frequency
90
–20
–40°C
0
20
40
60
80
CURRENT (mA)
Figure 21. Output Voltage Swing vs. Current (IOUT)
Figure 18. Channel Separation vs. Frequency
Rev. 0 | Page 9 of 20
100
06979-023
–20
100
06979-021
–100
AD8270
160
VS = ±15V
140
100pF
120
VS = ±5V
VS = ±2.5V
100
80
60
VS = ±18V
40
VS = ±15V
06979-024
20
1µs/DIV
0
Figure 22. Small Signal Step Response, Gain = 0.5
0
10
20
30
40
50
60
70
CAPACITIVE LOAD (pF)
80
90
100
Figure 25. Small Signal Overshoot with Capacitive Load, Gain = 0.5
80
VS = ±15V
33pF
70
220pF
60
50mV/DIV
OVERSHOOT (%)
0pF
VS = ±10V
06979-030
50mV/DIV
OVERSHOOT (%)
0pF
18pF
VS = ±10V
VS = ±5V
50
VS = ±2.5V
40
30
VS = ±18V
20
VS = ±15V
0
0
50
100
150
CAPACITIVE LOAD (pF)
200
06979-031
1µs/DIV
06979-025
10
Figure 26. Small Signal Overshoot with Capacitive Load, Gain = 1
Figure 23. Small Signal Step Response, Gain = 1
80
VS = ±15V
70
470pF
0pF 100pF
50ms/DIV
OVERSHOOT (%)
60
50
VS = ±10V
40
VS = ±5V
30
VS = ±2.5V
20
VS = ±18V
10
0
Figure 24. Small Signal Step Response, Gain = 2
0
50
100
150
200
250 300
350
CAPACITIVE LOAD (pF)
400
450
06979-032
06979-026
1µs/DIV
VS = ±15V
Figure 27. Small Signal Overshoot with Capacitive Load, Gain = 2
Rev. 0 | Page 10 of 20
AD8270
45
VS = ±15V
VIN = ±5V
1V/DIV
OUTPUT SLEW RATE (V/µs)
40
35
+SR
30
–SR
25
20
15
10
0
–45 –35 –25 –15 –5 5 15 25 35 45 55 65 75 85 95 105 115 125
TEMPERATURE (°C)
06979-036
1µs/DIV
06979-033
5
Figure 31. Output Slew Rate vs. Temperature
Figure 28. Large Signal Pulse Response Gain = 0.5
1k
Figure 29. Large Signal Pulse Response Gain = 1
100
GAIN = 1
10
1
10
100
1k
FREQUENCY (Hz)
10k
100k
Figure 32. Voltage Noise Spectral Density vs. Frequency, Referred to Output
VS = ±15V
VIN = ±5V
GAIN = 2
5V/DIV
GAIN = 1
06979-035
1µV/DIV
Figure 30. Large Signal Pulse Response, Gain = 2
1s/DIV
06979-042
GAIN = 1/2
1µs/DIV
06979-041
1µs/DIV
GAIN = 2
GAIN = 0.5
06979-034
2V/DIV
VOLTAGE NOISE (nV/√Hz)
VS = ±15V
VIN = ±5V
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
OFFSET (10µV/DIV)
NUMBER OF UNITS
180
150
120
90
60
–600
–400
–200
0
VOSI (µV)
200
400
600
0
Figure 34. Typical Distribution of Op Amp Voltage Offset
100
1
2
3
4
5
6
TIME (s)
7
8
9
10
06979-044
0
06979-014
30
Figure 37. Change in Op Amp Offset Voltage vs. Warm-Up Time
N: 1043
MEAN: 321.6
SD: 6.9
NUMBER OF UNITS
80
60
40
310
315
320
325
330
335
1s/DIV
06979-020
50pA/DIV
0
340
IBIAS (nA)
06979-028
20
Figure 38. 0.1 Hz to 10 Hz Current Noise of Internal Op Amp
Figure 35. Typical Distribution of Op Amp Bias Current
10
N: 1043
MEAN: 0.31
SD: 2.59
160
CURRENT NOISE (pA/√Hz)
120
100
80
60
40
1
0
–9
–6
–3
0
3
IOFFSET (nA)
6
9
12
0.1
1
10
100
1k
FREQUENCY (Hz)
10k
100k
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
06979-029
20
06979-027
NUMBER OF UNITS
140
AD8270
Size
13 –VS
14 OUTB
15 OUTA
16 +VS
THEORY OF OPERATION
The AD8270 fits two op amps and 14 resistors in a 4 mm ×
4 mm package.
DRIVING THE AD8270
_
_
+
+
10kΩ
REF1A 5
20kΩ
20kΩ
10kΩ
10kΩ
AD8270
20kΩ
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.
12 –IN1B
11 –IN2B
10 +IN2B
9 +IN1B
PACKAGE CONSIDERATIONS
20kΩ
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.
06979-059
+IN1A 4
10kΩ
10kΩ
REF1B 8
+IN2A 3
10kΩ
10kΩ
REF2B 7
–IN2A 2
10kΩ
REF2A 6
–IN1A 1
10kΩ
Figure 40. Functional Block Diagram
CIRCUIT INFORMATION
The AD8270 has two channels, each consisting of a high precision,
low distortion op amp and seven trimmed resistors. These resistors 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.
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.
AC Performance
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.
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.
Space between the leads and thermal pad should be as wide as
possible to minimize the risk of contaminants affecting performance. A thorough washing of the board is recommended after the
soldering process, especially if high accuracy performance is
required at high temperatures.
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.
POWER SUPPLIES
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.
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.
Rev. 0 | Page 13 of 20
AD8270
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.
The internal op amp voltage range may be relevant in the
following applications, and calculating the voltage at the
internal op amp is advised.
•
•
•
R2 (V )
R1 + R2 +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
06979-061
R2
R2 (V )
R1 + R2 +IN
Difference amplifier configurations using supply voltages
of less than ±4.5 V
Difference amplifier configurations with a reference
voltage near the rail
Single-ended amplifier configurations
Figure 41. Voltage Division in the Difference Amplifier Configuration
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.
Rev. 0 | Page 14 of 20
AD8270
APPLICATIONS INFORMATION
DIFFERENCE AMPLIFIER CONFIGURATIONS
SINGLE-ENDED 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.
The AD8270 can be configured for a wide variety of singleended configurations with gains ranging from −2 to +3.
Table 8 shows a subset of the possible configurations.
+IN
3
4
–IN
10kΩ
=
10kΩ
+IN
10kΩ
10kΩ
1
10kΩ
6
1
NC
2
NC
3
GND
+IN
4
15
–IN
10kΩ
=
+IN
10kΩ
5
10kΩ
2
3
+IN
4
15
–IN
=
10kΩ
+IN
10kΩ
20kΩ 20kΩ
5
2
NC
3
6
+VS + –VS
2
4
15
10kΩ
10kΩ
–IN
10kΩ
=
10kΩ
+IN
10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ
6
+VS + –VS
2
–VS +VS
NC = NO CONNECT
Figure 46. Gain = 1 Difference Amplifier, Referenced to Midsupply
10kΩ
10kΩ
5kΩ
6
5
16
5kΩ
–IN
5kΩ
1
2
3
+IN
10kΩ
4
10kΩ
15
10kΩ
10kΩ
–IN
10kΩ
=
10kΩ
+IN
10kΩ
5kΩ
5kΩ
10kΩ
20kΩ 20kΩ
5
06979-055
–IN
1
1
10kΩ
GND
10kΩ
10kΩ
+VS
NC
+IN
Figure 43. Gain = 1 Difference Amplifier, Referenced to Ground
16
+IN
10kΩ
16
–IN
GND
NC = NO CONNECT
10kΩ
10kΩ
10kΩ
Figure 45. Gain = 0.5 Difference Amplifier, Referenced to Midsupply
10kΩ
6
–IN
=
–VS
10kΩ
20kΩ 20kΩ
5kΩ
10kΩ
10kΩ
10kΩ
10kΩ
3
15
10kΩ
5
06979-054
–IN
+IN
10kΩ
20kΩ 20kΩ
Figure 42. Gain = 0.5 Difference Amplifier, Referenced to Ground
16
2
4
GND
10kΩ
–IN
5kΩ
20kΩ 20kΩ
5
16
5kΩ
GND
GND
06979-057
2
15
10kΩ
6
+VS + –VS
–VS +VS
2
06979-058
–IN
10kΩ
06979-053
16
1
06979-056
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.
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.
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
Gain and Reference
Gain of 0.5, Referenced to Ground
Gain of 0.5, Referenced to Midsupply
Gain of 1, Referenced to Ground
Gain of 1, Referenced to Midsupply
Gain of 2, Referenced to Ground
Gain of 2, Referenced to Midsupply
Pin 1
OUT
OUT
−IN
−IN
−IN
−IN
Pin 2
−IN
−IN
NC
NC
−IN
−IN
Channel A
Pin 3 Pin 4
+IN
GND
+IN
−VS
NC
+IN
NC
+IN
+IN
+IN
+IN
+IN
Pin 5
GND
+VS
GND
−VS
GND
−VS
Rev. 0 | Page 15 of 20
Pin 6
GND
+VS
GND
+VS
GND
+VS
Pin 12
OUT
OUT
−IN
−IN
−IN
−IN
Pin 11
−IN
−IN
NC
NC
−IN
−IN
Channel B
Pin 10 Pin 9
+IN
GND
+IN
−VS
NC
+IN
NC
+IN
+IN
+IN
+IN
+IN
Pin 8
GND
+VS
GND
−VS
GND
−VS
Pin 7
GND
+VS
GND
+VS
GND
+VS
AD8270
Table 8. Selected Single-Ended Configurations
Electrical Performance
Signal Gain
−2
−1.5
−1.4
−1.25
−1
−0.8
−0.667
−0.6
−0.5
−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
+0.6
+0.6
+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
+2.25
+2.4
+2.5
+3
Op Amp
Closed-Loop Gain
3
3
3
3
3
3
2
2
2
2
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
2
3
2
3
3
3
3
Pin Connections
Input
Resistance
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
8 kΩ
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
25 kΩ
16.67 kΩ
16 kΩ
15 kΩ
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
24 kΩ
16.67 kΩ
>1 GΩ
26.67 kΩ
25 kΩ
24 kΩ
>1 GΩ
10 kΩ −
Pin 1
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
OUT
OUT
OUT
OUT
IN
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
Rev. 0 | Page 16 of 20
10 kΩ −
Pin 2
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
NC
IN
GND
GND
NC
GND
GND
IN
IN
GND
GND
GND
GND
NC
GND
GND
NC
NC
GND
NC
GND
GND
GND
GND
10 kΩ +
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
IN
IN
IN
GND
IN
IN
IN
GND
IN
NC
IN
IN
IN
10 kΩ +
Pin 4
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
IN
IN
IN
IN
IN
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
NC
GND
GND
NC
NC
GND
IN
IN
IN
NC
NC
IN
GND
GND
IN
NC
IN
NC
IN
IN
NC
IN
IN
20 kΩ +
Pin 6
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
IN
GND
GND
IN
IN
GND
GND
GND
IN
AD8270
+OUT
16
14
13
V+IN – V–IN = V+OUT – V–OUT
VOCM = V+OUT + V–OUT
1
–IN
2
+IN
3
4
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
_
10kΩ
+
+
5
10kΩ
10kΩ
AD8270
20kΩ 20kΩ
Closed-Loop Gain
1.5
2
3
10kΩ
_
10kΩ
Table 9. Closed-Loop Gain of the Difference Amplifiers
12
11
+IN
10
–IN
+IN
+OUT
=
VOCM
–OUT
–IN
9
20kΩ 20kΩ
8
7
6
OCM
OCM
Figure 48. Differential Output, G = 1, Common-Mode Output Voltage
Set with Reference Voltage
Gain of 1 Configuration
+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 configurations are listed in Table 8.
DIFFERENTIAL OUTPUT
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.
16
1
–IN
2
+IN
3
A
4
10kΩ
10kΩ
10kΩ
–OUT
14
15
10kΩ
13
10kΩ
10kΩ
_
_
10kΩ
+
+
10kΩ
10kΩ
AD8270
20kΩ 20kΩ
5
10kΩ
V+IN – V–IN = V+OUT – V–OUT
V + VB
V+OUT + V–OUT = A
2
12
11
+IN
10
–IN
9
A
+IN
+OUT
=
VOCM
–OUT
–IN
20kΩ 20kΩ
7
6
8
VA + VB
2
B
06979-063
Difference Amplifier Gain
0.5
1
2
–OUT
15
06979-062
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).
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)
+12V
–12V
16
13
10kΩ
06979-060
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
NOTE:
POWER SUPPLY DECOUPLING
NOT SHOWN.
1
10kΩ
2
+IN
3
4
5
6
5V_REF
0.1µF
7
8
9
–IN
10
+IN
11
15
10kΩ
33Ω
10kΩ
4
2.7nF
COG
20kΩ
+IN
AD7688
33Ω
20kΩ
20kΩ
3
2.7nF
COG
–IN
REF
1
AD8270
0.1µF
+12V
20kΩ
2
10kΩ
VIN
10kΩ
14
10kΩ
VOUT 5
ADR435
5V_REF
10µF
GND
10kΩ
4
10kΩ
12
Figure 51. Driving an ADC
Rev. 0 | Page 18 of 20
06979-037
–IN
10kΩ
AD8270
OUTLINE DIMENSIONS
4.00
BSC SQ
0.60 MAX
0.60 MAX
13
PIN 1
INDICATOR
12° MAX
12
PIN 1
INDICATOR
1
2.50
2.35 SQ
2.20
EXPOSED
PAD
3.75
BSC SQ
0.50
0.40
0.30
(BOTTOM VIEW)
9
8
5
4
0.25 MIN
1.95 BSC
0.80 MAX
0.65 TYP
0.05 MAX
0.02 NOM
SEATING
PLANE
0.35
0.30
0.25
0.20 REF
COPLANARITY
0.08
COMPLIANT TO JEDEC STANDARDS MO-220-VGGC
010606-0
1.00
0.85
0.80
0.65 BSC
TOP
VIEW
16
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-R7 1
AD8270ACPZ-RL1
AD8270ACPZ-WP1
1
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
Z = RoHS Compliant Part.
Rev. 0 | Page 19 of 20
Package Option
CP-16-10
CP-16-10
CP-16-10
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
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