October 4, 2011
LM7131
Tiny High Speed Single Supply Operational Amplifier
General Description
Features
The LM7131 is a high speed bipolar operational amplifier
available in a tiny SOT23-5 package. This makes the LM7131
ideal for space and weight critical designs. Single supply voltages of 3V and 5V provides good video performance, wide
bandwidth, low distortion, and high PSRR and CMRR. This
makes the amplifier an excellent choice for desktop and
portable video and computing applications. The amplifier is
supplied in surface mount 8-pin and tiny SOT23-5 packages.
Tiny amplifiers are so small they can be placed anywhere on
a board close to the signal source or next to an A-to-D input.
Good high speed performance at low voltage makes the
LM7131 a preferred part for battery powered designs.
■ Tiny SOT23-5 package saves space-typical circuit layouts
■
■
■
■
■
■
■
■
■
take half the space of SO-8 designs.
Guaranteed specs at 3V, 5V, and ±5V supplies
Typical supply current 7.0 mA at 5V, 6.5 mA at 3V
4V output swing with +5V single supply
Typical total harmonic distortion of 0.1% at 4 MHz
70 MHz Gain-Bandwidth Product
90 MHz −3 dB bandwidth at 3V and 5V, Gain = +1
Designed to drive popular video A/D converters
40 mA output can drive 50Ω loads
Differential gain and phase 0.25% and 0.75° at AV = +2
Applications
■
■
■
■
■
Driving video A/D converters
Video output for portable computers and PDAs
Desktop teleconferencing
High fidelity digital audio
Video cards
Connection Diagrams
8-Pin SO-8
5-Pin SOT23-5
1231301
1231302
Top View
Top View
Ordering Information
THE FOLLOWING DEVICES WERE OBSOLETED IN MARCH 2003
Package
Ordering
Information
NSC Drawing
Number
Package
Marking
Supplied as
8-Pin SO-8
LM7131ACM
M08A
LM7131ACM
rails
8-Pin SO-8
LM7131BCM
M08A
LM7131BCM
rails
8-Pin SO-8
LM7131ACMX
M08A
LM7131ACM
2.5k units tape and reel
8-Pin SO-8
LM7131BCMX
M08A
LM7131BCM
2.5k units tape and reel
5-Pin SOT 23-5
LM7131ACM5
MA05A
A02A
1k units on tape and reel
5-Pin SOT 23-5
LM7131BCM5
MA05A
A02B
1k units on tape and reel
5-Pin SOT 23-5
LM7131ACM5X
MA05A
A02A
3k units tape and reel
5-Pin SOT 23-5
LM7131BCM5X
MA05A
A02B
3k units tape and reel
© 2011 National Semiconductor Corporation
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Print Date/Time: 2011/10/04 14:19:40
LM7131 Tiny High Speed Single Supply Operational Amplifier
OBSOLETE
LM7131
(soldering, 10 sec)
Storage Temperature Range
Junction Temperature (Note 4)
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Tolerance (Note 2)
Differential Input Voltage
Voltage at Input/Output Pin
Supply Voltage (V+ – V−)
Current at Input Pin
Current at Output Pin (Note 3)
Current at Power Supply Pin
Lead Temperature
260°C
− 65°C to +150°C
150°C
Operating Ratings
2000V
±2.0
(V+)+0.1V, (V−) − 0.3V
2.7V ≤ V ≤ 12V
Supply Voltage (V+ – V−)
Junction Temperature Range
LM7131AC, LM7131BC
12V
±5 mA
±80 mA
±80 mA
0°C ≤ TJ ≤ + 70°C
Thermal Resistance (θJA)
SO-8 Package, 8-Pin Surface Mount
M05A Package, 5-Pin Surface Mount
165°C/W
325°C/W
3V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for TJ = 25°C, V+ = 3V, V− = 0V, VCM = VO = V+/2 and RL = 150Ω. Boldface limits
apply at the temperature extremes.
Symbol
Parameter
Conditions
Typ
(Note 5)
LM7131AC
Limit
(Note 6)
LM7131BC
Limit
(Note 6)
Units
3.5
7
mV
4
10
VOS
Input Offset Voltage
0.02
TCVOS
Input Offset Voltage
10
max
μV/°C
Average Drift
IB
Input Bias Current
IOS
Input Offset Current
CMRR
Common Mode
0V ≤ VCM ≤ 0.85V
Rejection Ratio
(Video Levels)
Common Mode
0.85V ≤ VCM ≤ 1.7V
Rejection Ratio
(Mid-Range)
Positive Power Supply
V+ = 3V, V− = 0V
Rejection Ratio
V+ = 3V to 6.5V
Negative Power Supply
V− = −3V, V+ = 0V
Rejection Ratio
V− = −3V to −6.5V
Input Common-Mode
V+ = 3V
Voltage Range
For CMRR ≥ 50 dB
CMRR
+PSRR
−PSRR
VCM
AVOL
Voltage Gain
35
40
40
0.35
3.5
3.5
5
5
μA
max
75
60
60
dB
55
55
min
55
55
dB
50
50
min
65
65
dB
60
60
min
65
65
dB
60
60
min
70
75
75
0.0
0.0
V
0.00
0.00
min
2.0
1.70
1.60
1.70
1.60
V
max
60
55
55
dB
50
50
0.0
RL = 150Ω, VO = 0.250V
to 1.250V
CIN
Common-Mode
μA
max
35
20
2
pF
Input Capacitance
VO
Output Swing
V+ = 3V, RL = 150Ω
High
terminated at 0V
Low
V+ = 3V, RL = 150Ω
2.6
2.3
0.05
terminated at 0V
High
V+ = 3V, RL = 150Ω
2.6
terminated at 1.5V
Low
V+ = 3V, RL = 150Ω
0.5
terminated at 1.5V
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2.3
V
2.0
2.0
min
0.15
0.15
V
0.20
0.20
max
2.3
2.3
V
2.0
2.0
min
0.8
0.8
V
1.0
1.0
max
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VO
VO
ISC
Parameter
Output Swing
V+ = 3V, RL = 600Ω
High
terminated at 0V
Output Swing
V+ = 3V, RL = 600Ω
Low
terminated at 0V
Output Short Circuit
Sourcing, VO = 0V
LM7131AC
Limit
(Note 6)
Typ
(Note 5)
Conditions
max
V
0.06
max
65
Sinking, VO = 3V
Supply Current
Units
V
2.73
Current
IS
LM7131BC
Limit
(Note 6)
40
V+ = + 3V
6.5
45
45
mA
40
40
min
25
25
mA
20
20
min
9.0
9.0
mA
9.5
9.5
max
3V AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for TJ = 25°C, V+ = 3V, V− = 0V, VCM = VO = V+/2 and RL = 150Ω. Boldface limits
apply at the temperature extremes.
Symbol
T.H.D.
Parameter
Conditions
Total Harmonic Distortion
Typ
(Note 5)
F = 4 MHz, AV = + 2
LM7131AC
Limit
(Note 6)
LM7131BC
Limit
(Note 6)
Units
0.1
%
RL = 150Ω, VO = 1.0VPP
SR
Differential Gain
(Note 10)
0.45
%
Differential Phase
(Note 10)
0.6
°
Slew Rate
RL = 150Ω, CL = 5 pF
120
V/μS
100
V/μS
Gain-Bandwidth Product
70
MHz
Closed-Loop − 3 dB
Bandwidth
90
MHz
(Note 7)
SR
RL = 150Ω, CL = 20 pF
Slew Rate
(Note 7)
GBW
5V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for TJ = 25°C, V+ = 5V, V− = 0V, VCM = VO = V+/2 and RL = 150Ω. Boldface limits
apply at the temperature extremes.
Symbol
VOS
TCVOS
Parameter
Conditions
Input Offset Voltage
Input Offset Voltage
Typ
(Note 5)
LM7131AC
Limit
(Note 6)
LM7131BC
Limit
(Note 6)
0.02
3.5
7
mV
4
10
max
Units
μV/°C
10
Average Drift
IB
IOS
CMRR
CMRR
Input Bias Current
20
Input Offset Current
0.35
Common Mode
0V ≤ VCM ≤ 1.85V
Rejection Ratio
(Video Levels)
Common Mode
1.85V ≤ VCM ≤ 3.7V
Rejection Ratio
(Mid-Range)
75
70
35
40
40
3.5
3.5
5
5
μA
max
65
65
dB
60
60
min
55
55
dB
50
50
min
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μA
max
35
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LM7131
Symbol
LM7131
Symbol
Parameter
+ PSRR
− PSRR
VCM
AVOL
Conditions
Positive Power Supply
V+ = 5V, V− = 0V
Rejection Ratio
V+ = 5V to 10V
Negative Power Supply
V− = − 5V, V+ = 0V
Rejection Ratio
V− = − 5V to −10V
Input Common-Mode
V+ = 5V
Voltage Range
For CMRR ≥ 50 dB
Voltage Gain
Typ
(Note 5)
LM7131AC
Limit
(Note 6)
LM7131BC
Limit
(Note 6)
75
65
65
dB
60
60
min
65
65
dB
60
60
min
− 0.0
− 0.0
V
75
0.0
RL = 150Ω, VO =
0.00
0.00
min
4.0
3.70
3.60
3.70
3.60
V
max
70
60
60
dB
55
55
min
0.250V to 2.250V
CIN
Common-Mode
Units
2
pF
Input Capacitance
VO
Output Swing
V+ = 5V, RL = 150Ω
High
terminated at 0V
Low
V+ = 5V, RL = 150Ω
4.5
4.3
0.08
terminated at 0V
V+ = 5V, RL = 150Ω
High
4.5
terminated at 2.5V
V+ = 5V, RL = 150Ω
Low
0.5
terminated at 2.5V
VO
VO
ISC
Output Swing
V+ = 5V, RL = 600Ω
High
terminated at 0V
Ouptut Swing
V+ = 5V, RL = 600Ω
Low
terminated at 0V
Output Short Circuit
Sourcing, VO = 0V
65
Sinking, VO = 5V
40
Supply Current
V
4.0
4.0
min
0.15
0.15
V
0.20
0.20
max
4.3
4.3
V
4.0
4.0
min
0.8
0.8
V
1.0
1.0
max
V
4.70
max
V
0.07
max
Current
IS
4.3
V+ = +5V
7.0
45
45
mA
40
40
min
25
25
mA
20
20
min
9.5
9.5
mA
10.0
10.0
max
5V AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for TJ = 25°C, V+ = 5V, V− = 0V, VCM = VO = V+/2 and RL = 150Ω. Boldface limits
apply at the temperature extremes.
Symbol
T.H.D.
Parameter
Total Harmonic Distortion
Typ
(Note 5)
Conditions
F = 4 MHz, AV = +2
LM7131AC LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
0.1
%
RL = 150Ω, VO = 2.0VPP
SR
Differential Gain
(Note 10)
0.25
%
Differential Phase
(Note 10)
0.75
°
Slew Rate
RL = 150Ω, CL = 5 pF
150
V/μs
130
V/μs
70
MHz
(Note 8)
SR
Slew Rate
RL = 150Ω, CL = 20 pF
(Note 8)
GBW
Gain-Bandwidth Product
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Parameter
Typ
(Note 5)
Conditions
Closed-Loop −3 dB
Bandwidth
en
Input-Referred
LM7131AC LM7131BC
Limit
Limit
(Note 6)
(Note 6)
90
f = 1 kHz
11
f = 1 kHz
3.3
Units
MHz
Voltage Noise
in
Input-Referred
Current Noise
±5V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for TJ = 25°C, V+ = 5V, V− = 5V, VCM = VO = 0V and RL = 150Ω. Boldface limits
apply at the temperature extremes.
Symbol
Parameter
Conditions
Typ
(Note 5)
LM7131AC
Limit
(Note 6)
LM7131BC
Limit
(Note 6)
Units
3.5
7
mV
4
10
VOS
Input Offset Voltage
0.02
TCVOS
Input Offset Voltage
10
max
μV/°C
Average Drift
IB
IOS
CMRR
Input Bias Current
Input Offset Current
35
40
40
3.5
3.5
5
5
μA
max
65
65
dB
60
60
min
65
65
dB
60
60
min
65
65
dB
60
60
min
−5.0
−5.0
V
−5.0
−5.0
min
4.0
3.70
3.60
3.70
3.60
V
max
70
55
55
dB
50
50
0.35
−5V ≤ VCM ≤ 3.7V
75
Positive Power Supply
V+ = 5V, V− = 0V
75
Rejection Ratio
V+ = 5V to 10V
Negative Power Supply
V− = −5V, V+ = 0V
Rejection Ratio
V− = −5V to −10V
Input Common-Mode
V+ = 5V, V− = −5V
Voltage Range
For CMRR ≥ 60 dB
Common Mode
Rejection Ratio
+PSRR
−PSRR
VCM
AVOL
Voltage Gain
CIN
Common-Mode
75
−5.0
RL = 150Ω,
μA
max
35
20
VO = −2.0 to +2.0
2
pF
Input Capacitance
VO
ISC
Output Swing
V+ = 5V, V− = −5V
High
RL = 150Ω
Low
terminated at 0V
Output Short Circuit
Sourcing, VO = −5V
4.3
4.3
V
4.0
4.0
min
−4.5
−3.5
−2.5
−3.5
−2.5
V
max
65
45
45
mA
40
40
min
25
25
mA
20
20
min
10.5
10.5
mA
11.5
11.5
max
4.5
Current
Sinking, VO = 5V
IS
Supply Current
40
V+ = +5V, V− = −5V
7.5
5
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LM7131
Symbol
LM7131
±5V AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for TJ = 25°C, V+ = 5V, V− = 5V, VCM = VO = 0V and RL = 150Ω. Boldface limits
apply at the temperature extremes.
Symbol
T.H.D.
Parameter
Conditions
Total Harmonic Distortion
F = 4 MHz, AV = −2
Typ
(Note 5)
LM7131AC
Limit
(Note 6)
LM7131BC
Limit
(Note 6)
Units
1.5
%
RL = 150Ω, VO = 4.0VPP
SR
Differential Gain
(Note 10)
0.25
%
Differential Phase
(Note 10)
1.0
°
Slew Rate
RL = 150Ω, CL = 5 pF
150
V/μs
130
V/μs
Gain-Bandwidth Product
70
MHz
Closed-Loop −3 dB
Bandwidth
90
MHz
(Note 9)
SR
Slew Rate
RL = 150Ω, CL = 20 pF
(Note 9)
GBW
Note 1: Absolute maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical characteristics.
Note 2: Human body model, 1.5 kΩ in series with 100 pF.
Note 3: Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the
maximum allowed junction temperature of 150°C.
Note 4: The maximum power dissipation is a function of TJ(max), θJA, and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ
(max) - TA)/θJA. All numbers apply for packages soldered directly into a PC board.
Note 5: Typical values represent the most likely parametric norm.
Note 6: All limits are guaranteed by testing or statistical analysis.
Note 7: Connected as voltage follower with 1.5V step input. Number specified is the slower of the positive and negative slew rates. V+ = 3V and RL = 150Ω
connected to 1.5V. Amp excited with 1 kHz to produce VO = 1.5 VPP.
Note 8: Connected as Voltage Follower with 4.0V step input. Number specified is the slower of the positive and negative slew rates. V+ = 5V and RL = 150Ω
connected to 2.5V. Amp excited with 1 kHz to produce VO = 4 VPP.
Note 9: Connected as Voltage Follower with 4.0V step input. Number specified is the slower of the positive and negative slew rates. V+ = 5V, V− = −5V and
RL = 150Ω connected to 0V. Amp excited with 1 kHz to produce VO = 4 VPP.
Note 10: Differential gain and phase measured with a 4.5 MHz signal into a 150Ω load, Gain = +2.0, between 0.6V and 2.0V output.
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LM7131
Typical Performance Characteristics
LM7131 Supply Current vs
Supply Voltage
LM7131 Input Current vs
Temperature @ 3V
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LM7131 Input Current vs
Temperature @ 5V
LM7131 Input Current vs
Input Voltage @ 3V
1231329
1231330
LM7131 Input Current vs
Input Voltage @ 5V
LM7131 CMRR vs
Frequency @ 5V
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LM7131
LM7131 Voltage Noise vs
Frequency @ 3V
LM7131 Voltage Noise vs
Frequency @ 5V
1231333
1231334
LM7131 PSRR vs
Frequency @ 3V
LM7131 PSRR vs
Frequency @ 5V
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1231336
LM7131 Cable Driver
AV = +1 @ +3V
LM7131 Cable Driver
AV = +2 @ +3V
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LM7131
LM7131 Driving 5′
RG-59 AV = +2 @ +3V
LM7131 Driving 75′
RG-59 AV = +2 @ +3V
1231339
1231340
LM7131 Cable Driver
AV = +10 @ +3V
LM7131 Cable Driver
AV = +1 @ +5V
1231341
1231342
LM7131 Driving 5′ RG-59
AV = +2 @ +5V
LM7131 Cable Driver
AV = +2 @ +5V
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LM7131
LM7131 Driving 75′ RG-59
AV = +2 @ +5V
LM7131 Cable Driver
AV = +10 @ +5V
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LM7131 Driving Flash
A/D Load AV = −1 @ +5V
LM7131 Driving Flash
A/D Load AV = +1 @ +5V
1231347
1231348
LM7131 Driving Flash
A/D Load AV = +2 @ +5V
LM7131 Driving Flash
A/D Load AV = +5 @ +5V
1231349
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LM7131
LM7131 Driving Flash
A/D Load AV = +5 @ +5V
With 2 pF Feedback Capacitor
LM7131 Driving Flash
A/D Load AV = +10 @ +5V
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LM7131 Bode Plot
@ 3V, 5V and 10V
LM7131 Single Supply
Bode Plot @ 3V, 5V and 10V
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LM7131
rotating helical scan video head (VCR) assemblies. This
avoids long cable runs for low level video signals, and can
result in higher signal fidelity.
Additional space savings parts are available in tiny packages
from National Semiconductor, including low power amplifiers,
precision voltage references, and voltage regulators.
Application Information
GENERAL INFORMATION
The LM7131 is a high speed complementary bipolar amplifier
which provides high performance at single supply voltages.
The LM7131 will operate at ±5V split supplies, +5V single
supplies, and +3V single supplies. It can provide improved
performance for ±5V designs with an easy transition to +5V
single supply. The LM7131 is a voltage feedback amplifier
which can be used in most operational amplifier circuits.
The LM7131 is available in two package types: SO-8 surface
mount package and the SOT23-5 Tiny package for space and
weight savings.
The LM7131 has been designed to meet some of the most
demanding requirements for single supply amplifiers—driving
analog to digital converters and video cable driving. The output stage of the LM7131 has been specially designed for the
dynamic load presented by analog to digital converters. The
LM7131 is capable of a 4V output range with a +5V single
supply. The LM7131's drive capability and good differential
gain and phase make quality video possible from a small
package with only a +5V supply.
Notes on Performance Curves and
Datasheet Limits
Important:
Performance curves represent an average of parts, and are
not limits.
SUPPLY CURRENT vs SUPPLY VOLTAGE
Note that this curve is nearly straight, and rises slowly as the
supply voltage increases.
INPUT CURRENT vs INPUT VOLTAGE
This curve is relatively flat in the 200 mV to 4V input range,
where the LM7131 also has good common mode rejection.
COMMON MODE VOLTAGE REJECTION
Note that there are two parts to the CMRR specification of the
datasheet for 3V and 5V. The common mode rejection ratio
of the LM7131 has been maximized for signals near ground
(typical of the active part of video signals, such as those which
meet the RS-170 levels). This can help provide rejection of
unwanted noise pick-up by cables when a balanced input is
used with good input resistor matching. The mid-level CMRR
is similar to that of other single supply op amps.
BENEFITS OF THE LM7131
The LM7131 can make it possible to amplify high speed signals with a single +5V or +3V supply, saving the cost of split
power supplies.
EASY DESIGN PATH FROM ±5V to +5V SYSTEMS
The SO-8 package and similar ±5V and single supply specifications means the LM7131 may be able to replace many
more expensive or slower op amps, and then be used for an
easy transition to 5V single supply systems. This could provide a migration path to lower voltages for the amplifiers in
system designs, reducing the effort and expense of testing
and re-qualifying different op amps for each new design.
In addition to providing a design migration path, the SOT23-5
Tiny surface mount package can save valuable board space.
BODE PLOTS (GAIN vs FREQUENCY FOR AV = +1)
The gain vs. frequency plots for a non-inverting gain of 1 show
the three voltages with the 150Ω load connected in two ways.
For the single supply graphs, the load is connected to the
most negative rail, which is ground. For the split supply
graphs, the load is connected to a voltage halfway between
the two supply rails.
SPECIFIC ADVANTAGES OF SOT23-5 (TINY PACKAGE)
The SOT23-5 (Tiny) package can save board space and allow
tighter layouts. The low profile can help height limited designs,
such as sub-notebook computers, consumer video equipment, personal digital assistants, and some of the thicker
PCMCIA cards. The small size can improve signal integrity in
noisy environments by placing the amplifier closer to the signal source. The tiny amp can fit into tight spaces and weighs
little. This makes it possible to design the LM7131 into places
where amplifiers could not previously fit.
The LM7131 can be used to drive coils and transformers referenced to virtual ground, such as magnetic tape heads and
disk drive write heads. The small size of the SOT23-5 package can allow it to be placed with a pre-amp inside of some
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DRIVING CABLES
Pulse response curves for driving 75Ω back terminate cables
are shown for both 3V and 5V supplies. Note the good pulse
fidelity with straight 150 loads, five foot (1.5 meter) and 75 foot
(22 meter) cable runs. The bandwidth is reduced when used
in a gain of ten (AV = +10). Even in a gain of ten configuration,
the output settles to < 1% in about 100 ns, making this useful
for amplifying small signals at a sensor or signal source and
driving a cable to the main electronics section which may be
located away from the signal source. This will reduce noise
pickup.
Please refer to Figures 1, 2, 3, 4, 5 for schematics of test setups for cable driving.
12
12313 Version 7 Revision 4
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LM7131
1231309
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 1. Cable Driver AV = +1
1231310
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 2. Cable Driver AV = +2
13
12313 Version 7 Revision 4
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www.national.com
LM7131
1231311
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 3. Cable Driver 5′ RG-59
1231312
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 4. Cable Driver 75′ RG-59
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LM7131
1231313
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 5. Cable Driver Gain of 10 AV = +10
capacitor across the feedback resistor. See Figure 9 and Figure 10 for schematics and respective performance curves for
flash A/D driving at AV = +5 with and without a 2 pF feedback
capacitor.
See section on feedback compensation. Ringing can also be
reduced by placing an isolation resistor between the output
and the analog-to-digital converter input—see sections on
driving capacitive loads and analog-to-digital converters.
Please refer to Figures 6, 7, 8, 9, 10, 11 for schematics of test
setups for driving flash A/D converters.
DRIVING TYPE 1175 FLASH A/D LOADS
The circuits in Figures 6, 7, 8, 9, 10, 11 show a LM7131 in a
voltage follower configuration driving the passive equivalent
of a typical flash A/D input. Note that there is a slight ringing
on the output, which can affect accurate analog-to-digital conversion. In these graphs, we have adjusted the ringing to be
a little larger than desirable in order to better show the settling
time. Most settling times at low gain are about 75 ns to < 1%
of final voltage. The ringing can be reduced by adding a low
value (approximately 500Ω) feedback resistor from the output
to the inverting input and placing a small (picofarad range)
1231314
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 6. Flash A/D AV = −1
15
12313 Version 7 Revision 4
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www.national.com
LM7131
1231315
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 7. Flash A/D AV = +1
1231316
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 8. Flash A/D AV = +2
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LM7131
1231317
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 9. Flash A/D AV = +5
1231318
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 10. Flash A/D AV = +5 with Feedback Capacitor
17
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www.national.com
LM7131
1231319
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 11. Flash A/D AV = +10
Output Short Circuits
The LM7131 has output short circuit protection, however, it is
not designed to withstand continuous short circuits, very fast
high energy transient voltage or current spikes, or shorts to
any voltage beyond the power supply rails. Designs should
reduce the number and energy level of any possible output
shorts, especially when used with ±5V supplies.
A resistor in series with the output, such as the 75Ω resistor
used to back terminate 75Ω cables, will reduce the effects of
shorts. For outputs which will send signals off the PC board
additional protection devices, such as diodes to the power
rails, zener-type surge suppressors, and varistors may be
useful.
Using the LM7131
LIMITS AND PRECAUTIONS
Supply Voltage
The absolute maximum supply voltage which may be applied
to the LM7131 is 12V. Designers should not design for more
than 10V nominal, and carefully check supply tolerances under all conditions so that the voltages do not exceed the
maximum.
Differential Input Voltage
Differential input voltage is the difference in voltage between
the non-inverting (+) input and the inverting input (−) of the op
amp. The absolute maximum differential input voltage is ±2V
across the inputs. This limit also applies when there is no
power supplied to the op amp. This may not be a problem in
most conventional op amp designs, however, designers
should avoid using the LM7131 as comparator or forcing the
inputs to different voltages. In some designs, diode protection
may be needed between the inputs. See Figure 12.
Thermal Management
Note that the SOT23-5 (Tiny) package has less power dissipation capability (325°/W) than the S0-8 package (115°/W).
This may cause overheating with ±5 supplies and heavy loads
at high ambient temps. This is less of a problem when using
+5V single supplies.
Example:
Driving a 150Ω load to 2.0V at a 40°C (104 °F) ambient temperature. (This is common external maximum temperature for
office environments. Temperatures inside equipment may be
higher.)
No load powerNo load LM7131 supply current - 9.0 mA
Supply voltage is 5.0V
No load LM7131 power - 9.0 mA x 5.0V = 45 mW
Power with loadCurrent out is 2.0V/150 Ω = 13.33 mA
Voltage drop in LM7131 is 5.0V (supply) − 2.0V (output) =
3.0V
Power dissipation 13.33 mA x 3.0V = 40 mW
Total Power = 45 mW + 40 mW = 85 mW = 0.085
Temperature Rise = 0.085 W x 325°/W = 27.625 degrees
Junction temperature at 40° ambient = 40 + 27.625 =
67.6225°.
This device is within the 0° to 70° specification limits.
Gain of +2
1231320
FIGURE 12.
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to the signal of interest. Using lower input impedances is recommended to reduce this error source.
Feedback Resistor Values and Feedback Compensation
Using large values of feedback resistances (roughly 2k) with
low gains (such gains of 2) will result in degraded pulse response and ringing. The large resistance will form a pole with
the input capacitance of the inverting input, delaying feedback
to the amplifier. This will produce overshoot and ringing. To
avoid this, the gain setting resistors should be scaled to lower
values (below 1k) At higher gains (> 5) larger values of feedback resistors can be used.
Overshoot and ringing of the LM7131 can be reduced by
adding a small compensation capacitor across the feed back
resistor. For the LM7131 values in pF to tens of pF range are
useful initial values. Too large a value will reduce the circuit
bandwidth and degrade pulse response.
Since the small stray capacitance from the circuit layout, other
components, and specific circuit bandwidth requirements will
vary, it is often useful to select final values based on prototypes which are similar in layout to the production circuit
boards.
Layout and Power Supply Bypassing
Since the LM7131 is a high speed (over 50 MHz) device, good
high speed circuit layout practices should be followed. This
should include the use of ground planes, adequate power
supply bypassing, removing metal from around the input pins
to reduce capacitance, and careful routing of the output signal
lines to keep them away from the input pins.
The power supply pins should be bypassed on both the negative and positive supply inputs with capacitors placed close
to the pins. Surface mount capacitors should be used for best
performance, and should be placed as close to the pins as
possible. It is generally advisable to use two capacitors at
each supply voltage pin. A small surface mount capacitor with
a value of around 0.01 microfarad (10 nF), usually a ceramic
type with good RF performance, should be placed closest to
the pin. A larger capacitor, in usually in the range of 1.0 μF to
4.7 μF, should also be placed near the pin. The larger capacitor should be a device with good RF characteristics and low
ESR (equivalent series resistance) for best results. Ceramic
and tantalum capacitors generally work well as the larger capacitor.
For single supply operation, if continuous low impedance
ground planes are available, it may be possible to use bypass
capacitors between the +5V supply and ground only, and reduce or eliminate the bypass capacitors on the V− pin.
Reflections
The output slew rate of the LM7131 is fast enough to produce
reflected signals in many cables and long circuit traces. For
best pulse performance, it may be necessary to terminate cables and long circuit traces with their characteristic
impedance to reduce reflected signals.
Reflections should not be confused with overshoot. Reflections will depend on cable length, while overshoot will depend
on load and feedback resistance and capacitance. When determining the type of problem, often removing or drastically
shortening the cable will reduce or eliminate reflections. Overshoot can exist without a cable attached to the op amp output.
Driving Flash A/D Converters (Video Converters)
The LM7131 has been optimized to drive flash analog to digital converters in a +5V only system. Different flash A/D
converters have different voltage input ranges. The LM7131
has enough gain-bandwidth product to amplify standard video
level signals to voltages which match the optimum input range
of many types of A/D converters.
For example, the popular 1175 type 8-bit flash A/D converter
has a preferred input range from 0.6V to 2.6V. If the input
signal has an active video range (excluding sync levels) of
approximately 700 mV, a circuit like the one in Figure 13 can
be used to amplify and drive an A/D. The 10 μF capacitor
blocks the DC components, and allows the + input of the
LM7131 to be biased through R clamp so that the minimum
output is equal to VRB of the A/D converter. The gain of the
circuit is determined as follows:
Output Signal Range = 2.6V (V top) = 0.6V (V bottom) =
2.0V
Gain = Output Signal Range/Input Signal = 2.857 =
2.00/0.700
Gain = (Rf/R1) +1 = (249Ω/133Ω) +1
R isolation and Cf will be determined by the designer based
on the A/D input capacitance and the desired pulse response
of the system. The nominal values of 33Ω and 5.6 pF shown
in the schematic may be a useful starting point, however, signal levels, A/D converters, and system performance requirements will require modification of these values.
The isolation resistor, R isolation should be placed close to
the output of the LM7131, which should be close to the A/D
input for best results.
Capacitive Load Driving
The phase margin of the LM7131 is reduced by driving large
capacitive loads. This can result in ringing and slower settling
of pulse signals. This ringing can be reduced by placing a
small value resistor (typically in the range of 22Ω–100Ω) between the LM7131 output and the load. This resistor should
be placed as close as practical to the LM7131 output. When
driving cables, a resistor with the same value as the characteristic impedance of the cable may be used to isolate the
cable capacitance from the output. This resistor will reduce
reflections on the cable.
Input Current
The LM7131 has typical input bias currents in the 15 μA to
25 μA range. This will not present a problem with the low input
impedances frequently used in high frequency and video circuits. For a typical 75Ω input termination, 20 μA of input
current will produce a voltage across the termination resistor
of only 1.5 mV. An input impedance of 10 kΩ, however, would
produce a voltage of 200 mV, which may be large compared
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www.national.com
LM7131
The 325°/W value is based on still air and the pc board land
pattern shown in this datasheet. Actual power dissipation is
sensitive to PC board connections and airflow.
SOT23-5 power dissipation may be increased by airflow or by
increasing the metal connected to the pads, especially the
center pin (pin number 2, V−) on the left side of the SOT23-5.
This pin forms the mounting paddle for the die inside the
SOT23-5, and can be used to conduct heat away from the die.
The land pad for pin 2 can be made larger and/or connected
to power planes in a multilayer board.
Additionally, it should be noted that difficulty in meeting performance specifications for the LM7131 is most common at
cold temperatures. While excessively high junction temperatures will degrade LM7131 performance, testing has confirmed that most specifications are met at a junction
temperature of 85°C.
See “Understanding Integrated Circuit Package Power Capabilities”, Application Note AN-336, which may be found in
the appendix of the Operational Amplifier Databook.
LM7131
protection, sync, and possibly some type of gain control for varying
signal levels.
R clamp is connected to a voltage level which will result in the
bottom of the video signal matching the Vrb level of the A/D
converter. This level will need to be set by clamping the black
level of the video signal. The clamp voltage will depend on the
level and polarity of the video signal. Detecting the sync signal
can be done by a circuit such as the LM1881 Video Sync
Separator.
Some A/D converters have wide input ranges where the lower
reference level can be adjusted. With these converters, best
distortion results are obtained if the lower end of the output
range is about 250 mV or more above the V− input of the
LM7131 more. The upper limit can be as high as 4.0V with
good results.
Note: This is an illustration of a conceptual use of the LM7131, not a complete design. The circuit designer will need to modify this for input
1231321
FIGURE 13.
CCD Amplifiers
The LM7131 has enough gain bandwidth to amplify low level
signals from a CCD or similar image sensor and drive a flash
analog-to-digital converter with one amplifier stage.
Signals from CCDs, which are used in scanners, copiers, and
digital cameras, often have an output signal in the 100 mV–
300 mV range. See Figure 14 for a conceptual diagram. With
a gain of 6 the output to the flash analog-to- digital converter
is 1.8V, matching 90% of the converter's 2V input range. With
a −3db bandwidth of 70 MHz for a gain of +1, the bandwidth
at a gain of 6 will be 11.6 MHz. This 11.6 MHz bandwidth will
result in a time constant of about 13.6 ns. This will allow the
output to settle to 7 bits of accuracy within 4.9 time constants,
or about 66 ns. Slewing time for a 1.8V step will be about 12
ns. The total slewing and settling time will be about 78 ns of
the 150 ns pixel valid time. This will leave about 72 ns total
for the flash converter signal acquisition time and tolerance
for timing signals.
For scanners and copiers with moving scan bars, the
SOT23-5 package is small enough to be placed next to the
light sensor. The LM7131 can drive a cable to the main electronics section from the scan bar. This can reduce noise
pickup by amplifying the signal before sending on the cable.
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A/D Reference Drivers
The LM7131's output and drive capability make it a good
choice for driving analog-to-digital references which have
suddenly changing loads. The small size of the SOT23-5
package allow the LM7131 to be placed very close to the A/
D reference pin, maximizing response. The small size avoids
the penalty of increased board space. Often the SOT23-5
package is small enough that it can fit in space used by the
large capacitors previously attached to the A/D reference. By
acting as a buffer for a reference voltage, noise pickup can
be reduced and the accuracy may be increased.
For additional space savings, the LM4040 precision voltage
reference and LM385 low current voltage reference are available in a tiny SOT23-3 package.
Video Gain of +2
The design of the LM7131 has been optimized for gain of +2
video applications. Typical values for differential gain and
phase are 0.25% differential gain and 0.75 degree differential
phase. See Figure 12.
Improving Video Performance
Differential gain and phase performance can be improved by
keeping the active video portion of the signal above 300 mV.
20
12313 Version 7 Revision 4
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portable equipment, personal digital devices, and desktop
video applications.
The LM7131 can also supply +2.00V to a 50Ω load to ground,
making it useful as driver in 50Ω systems such as portable
test equipment.
Cable Driving with +3V Supplies
The LM7131 can drive 150Ω to 2.00V when supplied by a 3V
supply. This 3V performance means that the LM7131 is useful
in battery powered video applications, such as camcorders,
portable video mixers, still video cameras, and portable scanners.
Cable Driving with +5V Supplies
The LM7131 can easily drive a back-terminated 75Ω video
cable (150Ω load) when powered by a +5V supply. See Figures 2, 3, 4. This makes it a good choice for video output for
1231323
FIGURE 14. CCD Amplifier
one diode drop (roughly, 0.7V) to the supply rail. This leaves
a relatively wide range for +5V systems and a somewhat narrow range for +3V systems. One way to increase this output
range is to have the output load referenced to ground—this
will allow the output to swing lower. Another is to use higher
load impedances. The output swing specifications show typical numbers for swing with loads of 600Ω to ground. Note that
these typical numbers are similar to those for a 150Ω load.
These typical numbers are an indication of the maximum DC
performance of the LM7131.
The sinking output of the LM7131 is somewhat lower than the
amplifier's sourcing capability. This means that the LM7131
will not drive as much current into a load tied to 2.5 V as it will
drive into a load tied to 0V.
Good AC performance will require keeping the output further
away from the supply rails. For a +5V supply and relatively
high impedance load (analog-to-digital converter input) the
following are suggested as an initial starting range for achieving high (> 60 dB) AC accuracy
Upper output level—
Audio and High Frequency Signal Processing
The LM7131 is useful for high fidelity audio and signal processing. A typical LM7131 is capable of driving 2V across
150Ω (referenced to ground) at less than 0.1% distortion at
4 MHz when powered by a single 5V supply.
Use with 2.5V Virtual Ground Systems
with +5V Single Supply Power
Many analog systems which must work on a single +5V supply use a “virtual ground” - a reference voltage for the signal
processing which is usually between +5V and 0V. This virtual
ground is usually halfway between the top and bottom supply
rails. This is usually +2.5V for +5V systems and +1.5V for +3V
systems.
The LM7131 can be used in single supply/virtual ground systems driving loads referenced to 2.5V. The output swing
specifications in the data sheet show the tested voltage limits
for driving a 150Ω load to a virtual ground supply for +3V and
+5V. A look at the output swing specifications shows that for
heavy loads like 150 ohms, the output will swing as close as
21
12313 Version 7 Revision 4
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www.national.com
LM7131
The sync signal can go below 300 mV without affecting the
video quality. If it is possible to AC couple the signal and shift
the output voltage slightly higher, much better video performance is possible. For a +5V single supply, an output range
between 2.0V and 3.0V can have a differential gain of 0.07%
and differential phase of 0.3 degree when driving a 150Ω load.
For a +3V single supply, the output should be between 1.0V
and 2.0V.
LM7131
Approximately 0.8V to 1V below the positive (V+) rail.
Lower output level—
Approximately 200 mV–300 mV above the negative rail.
The LM7131 very useful in virtual ground systems as an output device for output loads which are referenced to 0V or the
lower rail. It is also useful as a driver for capacitive loads, such
as sample and hold circuits, and audio analog to digital converters. If fast amplifiers with rail-to-rail output ranges are
needed, please see the National Semiconductor LM6142
datasheet.
differential input voltage limit of ±2V, it may be necessary to
add protection diodes to the inputs. See Figure 15. For high
speed applications, it may be useful to consider low capacitance schottky diodes. Additional feedback capacitance may
be needed to control ringing due to the additional input capacitance from the D/A and protection diodes. When used
with current output D/As, the input bias currents may produce
a DC offset in the output. This offset may be canceled by a
resistor between the positive input and ground.
Spice Macromodel
A SPICE macromodel of the LM7131 and many other National Semiconductor op amps is available at no charge from
your National Semiconductor representative.
D/A Output Amplifier
The LM7131 can be used as an output amplifier for fast digitalto-analog converters. When using the LM7131 with converters with an output voltage range which may exceed the
1231324
FIGURE 15. D/A Ouput Amplifier
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12313 Version 7 Revision 4
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LM7131
SOT-23-5 Tape and Reel
Specification
TAPE FORMAT
Tape Section
#Cavaties
Cavity Status
Cover Tape Status
Leader
0 (min)
Empty
Sealed
(Start End)
75 (min)
Empty
Sealed
Carrier
3000
Filled
Sealed
1000
Filled
Sealed
Trailer
125 (min)
Empty
Sealed
(Hub End)
0 (min)
Empty
Sealed
TAPE DIMENSIONS
1231325
8 mm
0.130
(3.3)
0.124
(3.15)
0.130
(3.3)
0.126
(3.2)
0.138 ±0.002
(3.5 ±0.05)
0.055 ±0.004
(1.4 ±0.11)
0.157
(4)
0.315 ±0.012
(8 ±0.3)
Tape Size
DIM A
DIM Ao
DIM B
DIM Bo
DIM F
DIM Ko
DIM P1
DIM W
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LM7131
REEL DIMENSIONS
1231326
8 mm
7.00
330.00
0.059
1.50
0.512
13.00
0.795
20.20
2.165
55.00
0.331 +0.059/−0.000
8.4 + 1.50/−0.00
0.567
14.40
W1 + 0.078/−0.039
W1 + 2.00/−1.00
Tape Size
A
B
C
D
N
W1
W2
W3
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12313 Version 7 Revision 4
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LM7131
Physical Dimensions inches (millimeters) unless otherwise noted
5-Pin SOT Package
Order Package Number LM7131ACM5, LM7131ACM5X, LM7131BCM5 or LM7131BCM5X
NS Package Number MA05A
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12313 Version 7 Revision 4
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LM7131 Tiny High Speed Single Supply Operational Amplifier
Notes
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