NSC LM7131BCM5X

LM7131
Tiny High Speed Single Supply Operational Amplifier
General Description
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.
Features
n Tiny SOT23-5 package saves space-typical circuit
layouts take half the space of SO-8 designs.
n
n
n
n
n
n
n
n
n
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
n
n
n
n
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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
DS012313-1
DS012313-2
Top View
Package
Top View
Ordering
NSC Drawing
Package
Information
Number
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
© 1999 National Semiconductor Corporation
DS012313
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LM7131 Tiny High Speed Single Supply Operational Amplifier
September 1999
Absolute Maximum Ratings (Note 1)
(soldering, 10 sec)
Storage Temperature Range
Junction Temperature (Note 4)
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
12V
± 5 mA
± 80 mA
± 80 mA
Supply Voltage (V+ – V−)
Junction Temperature Range
LM7131AC, LM7131BC
Thermal Resistance (θJA)
SO-8 Package, 8-Pin Surface Mount
M05A Package, 5-Pin Surface Mount
2.7V ≤ V ≤ 12V
0˚C ≤ TJ ≤ + 70˚C
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
VOS
TCVOS
Parameter
Conditions
Typ
(Note 5)
Input Offset Voltage
0.02
Input Offset Voltage
LM7131AC
LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
3.5
7
mV
4
10
max
10
µV/˚C
Average Drift
IB
IOS
CMRR
CMRR
+PSRR
Input Bias Current
Input Offset Current
Common Mode
0V ≤ VCM ≤ 0.85V
(Video Levels)
Common Mode
0.85V ≤ VCM ≤ 1.7V
Rejection Ratio
(Mid-Range)
V+ = 3V, V− = 0V
V+ = 3V to 6.5V
Positive Power Supply
Input Common-Mode
V− = −3V, V+ = 0V
V− = −3V to −6.5V
V+ = 3V
Voltage Range
For CMRR ≥ 50 dB
Negative Power Supply
Rejection Ratio
VCM
0.35
Rejection Ratio
Rejection Ratio
−PSRR
20
75
70
75
75
0.0
2.0
AVOL
Voltage Gain
RL = 150Ω, VO = 0.250V
60
to 1.250V
CIN
Common-Mode
35
35
µA
40
40
max
3.5
3.5
µA
5
5
max
60
60
dB
55
55
min
55
55
dB
50
50
min
65
65
dB
60
60
min
65
65
dB
60
60
min
0.0
0.0
V
0.00
0.00
min
1.70
1.70
V
1.60
1.60
max
55
55
dB
50
50
2
pF
Input Capacitance
VO
VO
Output Swing
V+ = 3V, RL = 150Ω
High
Low
terminated at 0V
V+ = 3V, RL = 150Ω
High
terminated at 0V
V+ = 3V, RL = 150Ω
Low
terminated at 1.5V
V+ = 3V, RL = 150Ω
Output Swing
terminated at 1.5V
V+ = 3V, RL = 600Ω
High
terminated at 0V
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2.6
0.05
2.6
0.5
2.73
2.3
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
V
max
2
3V DC Electrical Characteristics
(Continued)
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
VO
ISC
Parameter
Conditions
Output Swing
V+ = 3V, RL = 600Ω
Low
terminated at 0V
Sourcing, VO = 0V
Output Short Circuit
Typ
(Note 5)
LM7131AC
LM7131BC
Limit
Limit
(Note 6)
(Note 6)
0.06
V
max
65
Current
Sinking, VO = 3V
IS
Supply Current
Units
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
Typ
(Note 5)
LM7131AC
LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
F = 4 MHz, AV = + 2
RL = 150Ω, VO = 1.0VPP
0.1
%
Differential Gain
(Note 10)
0.45
%
Differential Phase
0.6
˚
120
V/µS
100
V/µS
Gain-Bandwidth Product
70
MHz
Closed-Loop − 3 dB
90
MHz
Total Harmonic Distortion
SR
Slew Rate
(Note 10)
RL = 150Ω, CL = 5 pF
SR
Slew Rate
(Note 7)
RL = 150Ω, CL = 20 pF
(Note 7)
GBW
Bandwidth
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
Typ
(Note 5)
Input Offset Voltage
0.02
Input Offset Voltage
LM7131AC
LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
3.5
7
mV
4
10
max
10
µV/˚C
Average Drift
IB
IOS
CMRR
CMRR
+ PSRR
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)
V+ = 5V, V− = 0V
Positive Power Supply
75
70
75
3
35
35
µA
40
40
max
3.5
3.5
µA
5
5
max
65
65
dB
60
60
min
55
55
dB
50
50
min
65
65
dB
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5V DC Electrical Characteristics
(Continued)
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
Parameter
75
Input Common-Mode
V+ = 5V
0.0
Voltage Range
For CMRR ≥ 50 dB
Negative Power Supply
Rejection Ratio
VCM
Typ
(Note 5)
V+ = 5V to 10V
V− = − 5V, V+ = 0V
V− = − 5V to −10V
Rejection Ratio
− PSRR
Conditions
4.0
AVOL
Voltage Gain
RL = 150Ω, VO =
70
0.250V to 2.250V
CIN
Common-Mode
LM7131AC
LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
60
60
65
65
min
dB
60
60
min
− 0.0
− 0.0
V
0.00
0.00
min
3.70
3.70
V
3.60
3.60
max
60
60
dB
55
55
min
2
pF
Input Capacitance
VO
VO
Output Swing
V+ = 5V, RL = 150Ω
High
Low
terminated at 0V
V+ = 5V, RL = 150Ω
High
terminated at 0V
V+ = 5V, RL = 150Ω
Low
terminated at 2.5V
V+ = 5V, RL = 150Ω
Output Swing
terminated at 2.5V
V+ = 5V, RL = 600Ω
High
VO
Ouptut Swing
Low
ISC
Output Short Circuit
terminated at 0V
V+ = 5V, RL = 600Ω
terminated at 0V
Sourcing, VO = 0V
4.5
0.08
4.5
0.5
IS
Supply Current
V
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
max
0.07
V
max
65
40
V+ = +5V
4.3
4.0
4.70
Current
Sinking, VO = 5V
4.3
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
Conditions
Typ
(Note 5)
LM7131AC LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
Total Harmonic Distortion
F = 4 MHz, AV = +2
RL = 150Ω, VO = 2.0VPP
0.1
%
Differential Gain
(Note 10)
0.25
%
Differential Phase
0.75
˚
150
V/µs
130
V/µs
Gain-Bandwidth Product
70
MHz
Closed-Loop −3 dB
90
MHz
SR
Slew Rate
(Note 10)
RL = 150Ω, CL = 5 pF
SR
Slew Rate
(Note 8)
RL = 150Ω, CL = 20 pF
(Note 8)
GBW
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4
5V AC Electrical Characteristics
(Continued)
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
Parameter
Conditions
Typ
(Note 5)
LM7131AC LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
Bandwidth
en
Input-Referred
f = 1 kHz
11
f = 1 kHz
3.3
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
VOS
TCVOS
Parameter
Conditions
Typ
(Note 5)
Input Offset Voltage
0.02
Input Offset Voltage
LM7131AC
LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
3.5
7
mV
4
10
max
10
µV/˚C
Average Drift
IB
IOS
CMRR
Input Bias Current
20
Input Offset Current
Common Mode
0.35
−5V ≤ VCM ≤ 3.7V
75
Rejection Ratio
+PSRR
V+ = 5V, V− = 0V
V+ = 5V to 10V
75
75
Input Common-Mode
V− = −5V, V+ = 0V
V− = −5V to −10V
V+ = 5V, V− = −5V
Voltage Range
For CMRR ≥ 60 dB
Positive Power Supply
Rejection Ratio
−PSRR
Negative Power Supply
Rejection Ratio
VCM
−5.0
4.0
AVOL
CIN
Voltage Gain
RL = 150Ω,
VO = −2.0 to +2.0
70
Common-Mode
35
35
µA
40
40
max
3.5
3.5
µA
5
5
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
3.70
3.70
V
3.60
3.60
max
55
55
dB
50
50
2
pF
Input Capacitance
VO
ISC
V+ = 5V, V− = −5V
RL = 150Ω
4.5
High
Low
terminated at 0V
−4.5
Output Swing
Output Short Circuit
Sourcing, VO = −5V
65
Current
Sinking, VO = 5V
IS
Supply Current
40
V+ = +5V, V− = −5V
5
7.5
4.3
4.3
V
4.0
4.0
min
−3.5
−3.5
V
−2.5
−2.5
max
45
45
mA
40
40
min
25
25
mA
20
20
min
10.5
10.5
mA
11.5
11.5
max
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± 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
Typ
(Note 5)
LM7131AC
LM7131BC
Limit
Limit
(Note 6)
(Note 6)
Units
F = 4 MHz, AV = −2
RL = 150Ω, VO = 4.0VPP
1.5
%
Differential Gain
(Note 10)
0.25
%
Differential Phase
1.0
˚
150
V/µs
130
V/µs
Gain-Bandwidth Product
70
MHz
Closed-Loop −3 dB
90
MHz
Total Harmonic Distortion
SR
Slew Rate
(Note 10)
RL = 150Ω, CL = 5 pF
SR
Slew Rate
(Note 9)
RL = 150Ω, CL = 20 pF
(Note 9)
GBW
Bandwidth
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.
Typical Performance Characteristics
LM7131 Supply Current vs
Supply Voltage
LM7131 Input Current vs
Temperature @ 3V
DS012313-27
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LM7131 Input Current vs
Temperature @ 5V
DS012313-28
6
DS012313-29
Typical Performance Characteristics
LM7131 Input Current vs
Input Voltage @ 3V
(Continued)
LM7131 Input Current vs
Input Voltage @ 5V
DS012313-30
LM7131 Voltage Noise vs
Frequency @ 3V
LM7131 CMRR vs
Frequency @ 5V
DS012313-31
LM7131 Voltage Noise vs
Frequency @ 5V
DS012313-33
LM7131 PSRR vs
Frequency @ 5V
DS012313-32
LM7131 PSRR vs
Frequency @ 3V
DS012313-34
LM7131 Cable Driver
AV = +1 @ +3V
DS012313-35
LM7131 Cable Driver
AV = +2 @ +3V
DS012313-37
DS012313-38
DS012313-36
7
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Typical Performance Characteristics
LM7131 Driving 5'
RG-59 AV = +2 @ +3V
(Continued)
LM7131 Driving 75'
RG-59 AV = +2 @ +3V
DS012313-39
LM7131 Cable Driver
AV = +1 @ +5V
DS012313-40
LM7131 Cable Driver
AV = +2 @ +5V
DS012313-42
LM7131 Driving 75' RG-59
AV = +2 @ +5V
LM7131 Driving 5' RG-59
AV = +2 @ +5V
LM7131 Cable Driver
AV = +10 @ +5V
LM7131 Driving Flash
A/D Load AV = +1 @ +5V
DS012313-41
DS012313-43
DS012313-45
DS012313-44
LM7131 Driving Flash
A/D Load AV = −1 @ +5V
DS012313-46
LM7131 Driving Flash
A/D Load AV = +2 @ +5V
DS012313-48
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LM7131 Cable Driver
AV = +10 @ +3V
LM7131 Driving Flash
A/D Load AV = +5 @ +5V
DS012313-49
8
DS012313-47
DS012313-50
Typical Performance Characteristics
(Continued)
LM7131 Driving Flash
A/D Load AV = +5 @ +5V
With 2 pF Feedback Capacitor
LM7131 Driving Flash
A/D Load AV = +10 @ +5V
DS012313-6
DS012313-5
LM7131 Bode Plot
@ 3V, 5V and 10V
DS012313-7
LM7131 Single Supply
Bode Plot @ 3V, 5V and 10V
DS012313-8
Application Information
proved 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.
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 im9
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Application Information
Notes on Performance Curves and
Datasheet Limits
(Continued)
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.
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.
BENEFITS OF THE LM7131
COMMON MODE VOLTAGE REJECTION
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.
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.
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
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.
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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.
10
Notes on Performance Curves and Datasheet Limits
(Continued)
DS012313-9
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 1. Cable Driver AV = +1
DS012313-10
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 2. Cable Driver AV = +2
DS012313-11
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 3. Cable Driver 5' RG-59
11
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Notes on Performance Curves and Datasheet Limits
(Continued)
DS012313-12
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 4. Cable Driver 75' RG-59
DS012313-13
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 5. Cable Driver Gain of 10 AV = +10
farad range) 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 (pico-
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12
Notes on Performance Curves and Datasheet Limits
(Continued)
DS012313-14
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 6. Flash A/D AV = −1
DS012313-15
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 7. Flash A/D AV = +1
13
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Notes on Performance Curves and Datasheet Limits
(Continued)
DS012313-16
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 8. Flash A/D AV = +2
DS012313-17
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 9. Flash A/D AV = +5
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14
Notes on Performance Curves and Datasheet Limits
(Continued)
DS012313-18
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 10. Flash A/D AV = +5 with Feedback Capacitor
DS012313-19
Numbers in parentheses are measured
fixture capacitances w/o DUT and load.
FIGURE 11. Flash A/D AV = +10
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.
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
15
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Using the LM7131
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.
(Continued)
Gain of +2
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.
DS012313-20
FIGURE 12.
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.
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
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.
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.
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
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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 to the signal of interest. Using lower input impedances is recommended to reduce this error source.
16
Using the LM7131
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
(Continued)
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.
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.
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.
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.
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.
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 protection, sync, and possibly some type of gain control for varying signal
levels.
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.
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.
17
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Using the LM7131
(Continued)
DS012313-21
FIGURE 13.
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.
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.
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.
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.
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.
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
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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
portable equipment, personal digital devices, and desktop
video applications.
18
Using the LM7131
ful in battery powered video applications, such as camcorders, portable video mixers, still video cameras, and portable
scanners.
(Continued)
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 use-
DS012313-23
FIGURE 14. CCD Amplifier
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.
Approximately 0.8V to 1V below the positive (V+) rail.
Lower output level —
Approximately 200 mV–300 mV above the negative rail.
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 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
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.
19
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Using the LM7131
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.
(Continued)
D/A Output Amplifier
The LM7131 can be used as an output amplifier for fast
digital-to-analog converters. When using the LM7131 with
converters with an output voltage range which may exceed
the 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
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.
DS012313-24
FIGURE 15. D/A Ouput Amplifier
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20
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
DS012313-25
8 mm
Tape Size
0.130
0.124
0.130
0.126
0.138 ± 0.002
0.055 ± 0.004
0.157
0.315 ± 0.012
(3.3)
(3.15)
(3.3)
(3.2)
(3.5 ± 0.05)
(1.4 ± 0.11)
(4)
(8 ± 0.3)
DIM A
DIM Ao
DIM B
DIM Bo
DIM F
DIM Ko
DIM P1
DIM W
21
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SOT-23-5 Tape and Reel Specification
(Continued)
REEL DIMENSIONS
DS012313-26
8 mm
Tape Size
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7.00
0.059
0.512
0.795
2.165
0.331 +0.059/−0.000
0.567
W1 + 0.078/−0.039
330.00
1.50
13.00
20.20
55.00
8.4 + 1.50/−0.00
14.40
W1 + 2.00/−1.00
A
B
C
D
N
W1
W2
W3
22
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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LM7131 Tiny High Speed Single Supply Operational Amplifier
Physical Dimensions