LM7131BCN - National Semiconductor

TL/H/12313

LM7131 Tiny High Speed Single Supply Operational Amplifier

March 1995

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 perform-

ance, 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 DIPs, surface mount 8-pin pack-

ages, 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

YTiny SOT23-5 package saves space-typical circuit lay-

outs take half the space of SO-8 designs.

YGuaranteed specs at 3V, 5V, and g5V supplies

YTypical supply current 7.0 mA at 5V, 6.5 mA at 3V

Y4V output swing with a5V single supply

YTypical total harmonic distortion of 0.1% at 4 MHz

Y70 MHz Gain-Bandwidth Product

Y90 MHz b3 dB bandwidth at 3V and 5V, Gain ea

YDesigned to drive popular video A/D converters

Y40 mA output can drive 50Xloads

YDifferential gain and phase 0.25% and 0.75§at AVe

Applications

YDriving video A/D converters

YVideo output for portable computers and PDAs

YDesktop teleconferencing

YHigh fidelity digital audio

YVideo cards

Connection Diagrams

8-Pin DIP/SO-8

TL/H/12313–1

Top View

5-Pin SOT23-5

TL/H/12313–2

Top View

Package Ordering NSC Drawing Package Supplied as

Information Number Marking

8-Pin DIP LM7131ACN N08E LM7131ACN rails

8-Pin DIP LM7131BCN N08E LM7131BCN rails

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 250 units on tape and reel

5-Pin SOT 23-5 LM7131BCM5 MA05A A02B 250 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

C1995 National Semiconductor Corporation RRD-B30M75/Printed in U. S. A.

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) 2000V

Differential Input Voltage g2.0

Voltage at Input/Output Pin (Va)a0.1V, (Vb)b0.3V

Supply Voltage (Va–V

) 12V

Current at Input Pin g5mA

Current at Output Pin (Note 3) g80 mA

Current at Power Supply Pin g80 mA

Lead Temperature (soldering, 10 sec) 260§C

Storage Temperature Range b65§Ctoa

150§C

Junction Temperature (Note 4) 150§C

Operating Ratings

Supply Voltage (Va–V

) 2.7V sVs12V

Junction Temperature Range

LM7131AC, LM7131BC 0§CsTJsa70§C

Thermal Resistance (iJA)

N Package, 8-Pin Molded DIP 115§C/W

SO-8 Package, 8-Pin Surface Mount 165§C/W

M05A Package, 5-Pin Surface Mount 325§C/W

3V DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJe25§C, Vae

3V, Vbe0V, VCM eVOeVa/2 and RLe150X.Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions (Note 5)

Typ LM7131AC LM7131BC

Units

Limit Limit

(Note 6) (Note 6)

VOS Input Offset Voltage 0.02 27mV

410max

TCVOS Input Offset Voltage 10 mV/§C

Average Drift

IBInput Bias Current 20 30 30 mA

40 40 max

IOS Input Offset Current 0.35 3.5 3.5 mA

55max

CMRR Common Mode 0V sVCM s0.85V 75 60 60 dB

Rejection Ratio (Video Levels) 55 55 min

CMRR Common Mode 0.85V sVCM s1.7V 70 55 55 dB

Rejection Ratio (Mid-Range) 50 50 min

aPSRR Positive Power Supply Vae3V, Vbe0V 75 65 65 dB

Rejection Ratio Vae3V to 6.5V 60 60 min

bPSRR Negative Power Supply Vbeb

3V, Vae0V 75 65 65 dB

Rejection Ratio Vbeb

3V to b6.5V 60 60 min

VCM Input Common-Mode Vae3V 0.0 0.0 0.0 V

Voltage Range For CMRR t50 dB 0.00 0.00 min

2.0 1.70 1.70 V

1.60 1.60 max

AVOL Voltage Gain RLe150X,V

Oe0.250V 60 55 55 dB

to 1.250V 50 50

CIN Common-Mode 2pF

Input Capacitance

3V DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJe25§C, Vae

3V, Vbe0V, VCM eVOeVa/2 and RLe150X.Boldface limits apply at the temperature extremes. (Continued)

Symbol Parameter Conditions (Note 5)

Typ LM7131AC LM7131BC

Units

Limit Limit

(Note 6) (Note 6)

VOOutput Swing Vae3V, RLe150X2.6 2.3 2.3 V

High terminated at 0V 2.0 2.0 min

Low Vae3V, RLe150X0.05 0.15 0.15 V

terminated at 0V 0.20 0.20 max

High Vae3V, RLe150X2.6 2.3 2.3 V

terminated at 1.5V 2.0 2.0 min

Low Vae3V, RLe150X0.5 0.8 0.8 V

terminated at 1.5V 1.0 1.0 max

VOOutput Swing Vae3V, RLe600X2.73 V

High terminated at 0V max

VOOutput Swing Vae3V, RLe600X0.06 V

Low terminated at 0V max

ISC Output Short Circuit Sourcing, VOe0V 65 45 45 mA

Current 40 40 min

Sinking, VOe3V 40 25 25 mA

20 20 min

ISSupply Current Vaea3V 6.5 8.0 8.0 mA

8.5 8.5 max

3V AC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJe25§C, Vae

3V, Vbe0V, VCM eVOeVa/2 and RLe150X.Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions (Note 5)

Typ LM7131AC LM7131BC

Units

Limit Limit

(Note 6) (Note 6)

T.H.D. Total Harmonic Distortion F e4 MHz, AVea20.1 %

RLe150X,V

Oe1.0VPP

Differential Gain (Note 10) 0.45 %

Differential Phase (Note 10) 0.6 §

SR Slew Rate RLe150X,C

Le5pF 120 V/mS

(Note 7)

SR Slew Rate RLe150X,C

Le20 pF 100 V/mS

(Note 7)

GBW Gain-Bandwidth Product 70 MHz

Closed-Loop b3dB 90 MHz

Bandwidth

5V DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJe25§C, Vae

5V, Vbe0V, VCM eVOeVa/2 and RLe150X.Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions (Note 5)

Typ LM7131AC LM7131BC

Units

Limit Limit

(Note 6) (Note 6)

VOS Input Offset Voltage 0.02 27mV

410max

TCVOS Input Offset Voltage 10 mV/§C

Average Drift

IBInput Bias Current 20 30 30 mA

40 40 max

IOS Input Offset Current 0.35 3.5 3.5 mA

55max

CMRR Common Mode 0V sVCM s1.85V 75 65 65 dB

Rejection Ratio (Video Levels) 60 60 min

CMRR Common Mode 1.85V sVCM s3.7V 70 55 55 dB

Rejection Ratio (Mid-Range) 50 50 min

aPSRR Positive Power Supply Vae5V, Vbe0V 75 65 65 dB

Rejection Ratio Vae5V to 10V 60 60 min

bPSRR Negative Power Supply Vbeb5V, Vae0V 75 65 65 dB

Rejection Ratio Vbeb5V to b10V 60 60 min

VCM Input Common-Mode Vae5V 0.0 b0.0 b0.0 V

Voltage Range For CMRR t50 dB 0.00 0.00 min

4.0 3.70 3.70 V

3.60 3.60 max

AVOL Voltage Gain RLe150X,V

Oe70 60 60 dB

0.250V to 2.250V 55 55 min

CIN Common-Mode 2pF

Input Capacitance

VOOutput Swing Vae5V, RLe150X4.5 4.3 4.3 V

High terminated at 0V 4.0 4.0 min

Low Vae5V, RLe150X0.08 0.15 0.15 V

terminated at 0V 0.20 0.20 max

High Vae5V, RLe150X4.5 4.3 4.3 V

terminated at 2.5V 4.0 4.0 min

Low Vae5V, RLe150X0.5 0.8 0.8 V

terminated at 2.5V 1.0 1.0 max

VOOutput Swing Vae5V, RLe600X4.70 V

High terminated at 0V max

VOOuptut Swing Vae5V, RLe600X0.07 V

Low terminated at 0V max

ISC Output Short Circuit Sourcing, VOe0V 65 45 45 mA

Current 40 40 min

Sinking, VOe5V 40 25 25 mA

20 20 min

ISSupply Current Vaea

5V 7.0 8.5 8.5 mA

9.0 9.0 max

5V AC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJe25§C, Vae

5V, Vbe0V, VCM eVOeVa/2 and RLe150X.Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions (Note 5)

Typ LM7131AC LM7131BC

Units

Limit Limit

(Note 6) (Note 6)

T.H.D. Total Harmonic Distortion F e4 MHz, AVea

20.1 %

RLe150X,V

Oe2.0VPP

Differential Gain (Note 10) 0.25 %

Differential Phase (Note 10) 0.75 §

SR Slew Rate RLe150X,C

Le5pF 150 V/ms

(Note 8)

SR Slew Rate RLe150X,C

Le20 pF 130 V/ms

(Note 8)

GBW Gain-Bandwidth Product 70 MHz

Closed-Loop b3dB 90 MHz

Bandwidth

enInput-Referred f e1 kHz 11 nV

Voltage Noise 0Hz

inInput-Referred f e1 kHz 3.3 pA

Current Noise 0Hz

g5V DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJe25§C, Va

e5V, Vbe5V, VCM eVOe0V and RLe150X.Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions (Note 5)

Typ LM7131AC LM7131BC

Units

Limit Limit

(Note 6) (Note 6)

VOS Input Offset Voltage 0.02 27mV

410max

TCVOS Input Offset Voltage 10 mV/§C

Average Drift

IBInput Bias Current 20 30 30 mA

40 40 max

IOS Input Offset Current 0.35 3.5 3.5 mA

55max

CMRR Common Mode b5V sVCM s3.7V 75 65 65 dB

Rejection Ratio 60 60 min

aPSRR Positive Power Supply Vae5V, Vbe0V 75 65 65 dB

Rejection Ratio Vae5V to 10V 60 60 min

bPSRR Negative Power Supply Vbeb

5V, Vae0V 75 65 65 dB

Rejection Ratio Vbeb

5V to b10V 60 60 min

VCM Input Common-Mode Vae5V, Vbeb

5V b5.0 b5.0 b5.0 V

Voltage Range For CMRR t60 dB b5.0 b5.0 min

4.0 3.70 3.70 V

3.60 3.60 max

AVOL Voltage Gain RLe150X,705555

VOeb

2.0 to a2.0 50 50

g5V DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJe25§C, Va

e5V, Vbe5V, VCM eVOe0V and RLe150X.Boldface limits apply at the temperature extremes. (Continued)

Symbol Parameter Conditions (Note 5)

Typ LM7131AC LM7131BC

Units

Limit Limit

(Note 6) (Note 6)

CIN Common-Mode 2pF

Input Capacitance

VOOutput Swing Vae5V, Vbeb

5V 4.5 4.3 4.3 V

High RLe150X4.0 4.0 min

Low terminated at 0V

b4.5 b3.5 b3.5 V

b2.5 b2.5 max

ISC Output Short Circuit Sourcing, VOeb

5V 65 45 45 mA

Current 40 40 min

Sinking, VOe5V 40 25 25 mA

20 20 min

ISSupply Current Vaea

5V, Vbeb

5V 7.5 99mA

10 10 max

g5V AC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJe25§C, Va

e5V, Vbe5V, VCM eVOe0V and RLe150X.Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions (Note 5)

Typ LM7131AC LM7131BC

Units

Limit Limit

(Note 6) (Note 6)

T.H.D. Total Harmonic Distortion F e4 MHz, AVeb

21.5 %

RLe150X,V

Oe4.0VPP

Differential Gain (Note 10) 0.25 %

Differential Phase (Note 10) 1.0 §

SR Slew Rate RLe150X,C

Le5pF 150 V/ms

(Note 9)

SR Slew Rate RLe150X,C

Le20 pF 130 V/ms

(Note 9)

GBW Gain-Bandwidth Product 70 MHz

Closed-Loop b3dB 90 MHz

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 kXin 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),iJA, and TA. The maximum allowable power dissipation at any ambient temperature is PDe

(TJ(max) -T

)/iJA. 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. Vae3V and RLe150X

connected to 1.5V. Amp excited with 1 kHz to produce VOe1.5 VPP.

Note 8: Connected as Voltage Follower with 4.0V step input. Number specified is the slower of the positive and negative slew rates. Vae5V and RLe150X

connected to 2.5V. Amp excited with 1 kHz to produce VOe4V

PP.

Note 9: Connected as Voltage Follower with 4.0V step input. Number specified is the slower of the positive and negative slew rates. Vae5V, Vbeb

5V and

RLe150Xconnected to 0V. Amp excited with 1 kHz to produce VOe4V

PP.

Note 10: Differential gain and phase measured with a 4.5 MHz signal into a 150Xload, Gain ea

2.0, between 0.6V and 2.0V output.

Typical Performance Characteristics

Supply Voltage

LM7131 Supply Current vs

Temperature @3V

LM7131 Input Current vs

Temperature @5V

LM7131 Input Current vs

Input Voltage @3V

LM7131 Input Current vs

Input Voltage @5V

LM7131 Input Current vs

Frequency @5V

LM7131 CMRR vs

Frequency @3V

LM7131 Voltage Noise vs

Frequency @5V

LM7131 Voltage Noise vs

Frequency @3V

LM7131 PSRR vs

Frequency @5V

LM7131 PSRR vs

AVea

1@a

LM7131 Cable Driver

AVea

2@a

LM7131 Cable Driver

TL/H/12313–3

Typical Performance Characteristics (Continued)

RG-59 AVea

2@a

LM7131 Driving 5Ê

RG-59 AVea

2@a

LM7131 Driving 75Ê

AVea

10 @a3V

LM7131 Cable Driver

AVea

1@a

LM7131 Cable Driver

AVea

2@a

LM7131 Cable Driver

AVea

2@a

LM7131 Driving 5ÊRG-59

AVea

2@a

LM7131 Driving 75ÊRG-59

AVea

10 @a5V

LM7131 Cable Driver

A/D Load AVeb

1@a

LM7131 Driving Flash

A/D Load AVea

1@a

LM7131 Driving Flash

A/D Load AVea

2@a

LM7131 Driving Flash

A/D Load AVea

5@a

LM7131 Driving Flash

TL/H/12313–4

Typical Performance Characteristics (Continued)

LM7131 Driving Flash

A/D Load AVea

5@a

With 2 pF Feedback Capacitor

TL/H/12313–5

LM7131 Driving Flash

A/D Load AVea

10 @a5V

TL/H/12313–6

LM7131 Bode Plot

@3V, 5V and 10V

Ref Level 0.000 dB /Div 1.000 dB

Split Supplies

AVea

Le150X

TL/H/12313–7

LM7131 Single Supply

Bode Plot @3V, 5V and 10V

Ref Level 0.000 dB /Div 1.000 dB

Single Supplies

AVea

Le150X

TL/H/12313–8

Application Information

GENERAL INFORMATION

The LM7131 is a high speed complementary bipolar amplifi-

er which provides high performance at single supply volt-

ages. The LM7131 will operate at g5V split supplies, a5V

single supplies, and a3V single supplies. It can provide im-

proved performance for g5V designs with an easy tran-

sition to a5V single supply. The LM7131 is a voltage feed-

back amplifier which can be used in most operational ampli-

fier circuits.

The LM7131 is available in three package types: DIPs for

through hole designs, SO-8 surface mount packages 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 amplifiersÐdriv-

ing 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 a5V

single supply. The LM7131’s drive capability and good dif-

ferential gain and phase make quality video possible from a

small package with only a a5V supply.

BENEFITS OF THE LM7131

The LM7131 can make it possible to amplify high speed

signals with a single a5V or a3V supply, saving the cost of

split power supplies.

EASY DESIGN PATH FROM g5V to a5V SYSTEMS

The DIP and SO-8 packages and similar g5V 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 ex-

pense of testing and re-qualifying different op amps for each

new design.

In addition to providing a design migration path, the three

packages types have other advantages.

The DIPs can be used for easy prototyping and through hole

boards. The SO-8 for surface mount board designs, and

using the SOT23-5 for a smaller surface mount package can

save valuable board space.

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 clos-

er 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 pack-

ages from National Semiconductor, including low power am-

plifiers, precision voltage references, and voltage regula-

tors.

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 bal-

anced input is used with good input resistor matching. The

mid-level CMRR is similar to that of other single supply op

amps.

BODE PLOTS (GAIN vs FREQUENCY FOR AVea

The gain vs. frequency plots for a non-inverting gain of 1

show the three voltages with the 150Xload connected in

two ways. For the single supply graphs, the load is connect-

ed 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.

DRIVING CABLES

Pulse response curves for driving 75Xback terminate ca-

bles 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 re-

duced when used in a gain of ten (AVea

10). Even in a

gain of ten configuration, the output settles to k1% 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– 5

for schematics of test setups

for cable driving.

Application Information (Continued)

TL/H/12313–9

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 1. Cable Driver AVea

TL/H/12313–10

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 2. Cable Driver AVea

TL/H/12313–11

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 3. Cable Driver 5ÊRG-59

Application Information (Continued)

TL/H/12313–12

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 4. Cable Driver 75ÊRG-59

TL/H/12313–13

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 5. Cable Driver Gain of 10 AVea

Application Information (Continued)

DRIVING TYPE 1175 FLASH A/D LOADS

The circuits in

Figures 6– 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 con-

version. In these graphs, we have adjusted the ringing to be

a little larger than desirable in order to better show the set-

tling time. Most settling times at low gain are about 75 ns to

k1% of final voltage. The ringing can be reduced by add-

ing a low value (approximately 500X) feedback resistor from

the output to the inverting input and placing a small (picofar-

ad range) capacitor across the feedback resistor. See

Fig-

ures 9

and

for schematics and respective performance

curves for flash A/D driving at AVea5 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 out-

put and the analog-to-digital converter inputÐsee sections

on driving capacitive loads and analog-to-digital converters.

Please refer to

Figures 6– 11

for schematics of test setups

for driving flash A/D converters.

TL/H/12313–14

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 6. Flash A/D AVeb

TL/H/12313–15

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 7. Flash A/D AVea

Application Information (Continued)

TL/H/12313–16

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 8. Flash A/D AVea

TL/H/12313–17

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 9. Flash A/D AVea

Application Information (Continued)

TL/H/12313–18

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 10. Flash A/D AVea

5 with Feedback Capacitor

TL/H/12313–19

Numbers in parentheses are measured

fixture capacitances w/o DUT and load.

FIGURE 11. Flash A/D AVea

Using the LM7131

LIMITS AND PRECAUTIONS

Supply Voltage

The absolute maximum supply voltage which may be ap-

plied to the LM7131 is 12V. Designers should not design for

more than 10V nominal, and carefully check supply toler-

ances under all conditions so that the voltages do not ex-

ceed the maximum.

Differential Input Voltage

Differential input voltage is the difference in voltage be-

tween the non-inverting (a) input and the inverting input

(b) of the op amp. The absolute maximum differential input

voltage is g2V 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 com-

parator or forcing the inputs to different voltages. In some

designs, diode protection may be needed between the in-

puts. See

Figure 12

Gain of a2

TL/H/12313–20

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. De-

signs should reduce the number and energy level of any

possible output shorts, especially when used with g5V sup-

plies.

A resistor in series with the output, such as the 75Xresistor

used to back terminate 75Xcables, 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 dissi-

pation capability (325§/W) than the S0-8 and DIP packages

(115§/W). This may cause overheating with g5 supplies

and heavy loads at high ambient temps. This is less of a

problem when using a5V single supplies.

Example:

Driving a 150Xload to 2.0V at a 40§C (104 §F) ambient

temperature. (This is common external maximum tempera-

ture for office environments. Temperatures inside equip-

ment may be higher.)

No load power-

No load LM7131 supply current - 9.0 mA

Supply voltage is 5.0V

No load LM7131 power - 9.0 mA x 5.0V e45 mW

Power with load-

Current out is 2.0V/150 Xe13.33 mA

Voltage drop in LM7131 is 5.0V (supply) b2.0V

(output) e3.0V

Power dissipation 13.33 mA x 3.0V e40 mW

Total Power e45 mW a40 mW e85 mW e

0.085

Temperature Rise e0.085Wx325

/W e27.625

degrees

Junction temperature at 40§ambient e40 a

27.625 e67.6225§.

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

the center pin (pin number 2, Vb) 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 per-

formance specifications for the LM7131 is most common at

cold temperatures. While excessively high junction tempera-

tures will degrade LM7131 performance, testing has con-

firmed that most specifications are met at a junction temper-

ature of 85§C.

See ‘‘Understanding Integrated Circuit Package Power Ca-

pabilities’’, Application Note AN-336, which may be found in

the appendix of the Operational Amplifier Databook.

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 neg-

ative 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 capaci-

tors at each supply voltage pin. A small surface mount ca-

pacitor with a value of around 0.01 microfarad (10 nF), usu-

ally 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 mFto4.7mF, 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 by-

pass capacitors between the a5V supply and ground only,

and reduce or eliminate the bypass capacitors on the Vb

pin.

Using the LM7131 (Continued)

Capacitive Load Driving

The phase margin of the LM7131 is reduced by driving large

capacitive loads. This can result in ringing and slower set-

tling of pulse signals. This ringing can be reduced by placing

a small value resistor (typically in the range of 22X–100X)

between the LM7131 output and the load. This resistor

should be placed as close as practical to the LM7131 out-

put. 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 mAto

25 mA range. This will not present a problem with the low

input impedances frequently used in high frequency and vid-

eo circuits. For a typical 75Xinput termination, 20 mAof

input current will produce a voltage across the termination

resistor of only 1.5 mV. An input impedance of 10 kX, how-

ever, 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.

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 (l5)

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 require-

ments 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 pro-

duce 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 character-

istic impedance to reduce reflected signals.

Reflections should not be confused with overshoot. Reflec-

tions will depend on cable length, while overshoot will de-

pend on load and feedback resistance and capacitance.

When determining the type of problem, often removing or

drastically shortening the cable will reduce or eliminate re-

flections. 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 a5V only system. Different flash A/D

converters have different voltage input ranges. The LM7131

has enough gain-bandwidth product to amplify standard vid-

eo 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 convert-

er 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 mF capacitor

blocks the DC components, and allows the ainput 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 e2.6V (V top) e0.6V (V bot-

tom) e2.0V

Gain eOutput Signal Range/Input Signal e2.857

e2.00/0.700

Gain e(Rf/R1)a1e(249X/133X)a1

R isolation and Cfwill be determined by the designer based

on the A/D input capacitance and the desired pulse re-

sponse of the system. The nominal values of 33Xand 5.6

pF shown in the schematic may be a useful starting point,

however, signal levels, A/D converters, and system per-

formance 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 de-

pend 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.

Important 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 convert-

ers, best distortion results are obtained if the lower end of

the output range is about 250 mV or more above the Vb

input of the LM7131 more. The upper limit can be as high as

4.0V with good results.

Driving the ADC12062 a5V 12-BIT A/D Converter

Figure 14

shows the LM7131 driving a National ADC12062

12 bit analog to digital converter. Both devices can be pow-

ered from a single a5V supply, lowering system complexity

and cost. With the lowest signal voltage limited to 300 mV

and a 3.8V peak-to-peak 100 KHz signal, bench tests have

shown distortion less than b75 db, signal to noise ratios

greater than 66 db, and SINAD (signal to noise adistortion)

values greater than 65 db. For information on the latest sin-

gle supply analog-to-digital converters, please contact your

National Semiconductor representative.

Using the LM7131 (Continued)

TL/H/12313–21

FIGURE 13

TL/H/12313–22

FIGURE 14. Buffering the Input with an LM7131 High Speed Op Amp

Using the LM7131 (Continued)

CCD Amplifiers

The LM7131 has enough gain bandwidth to amplify low lev-

el 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 15

for a conceptual dia-

gram. 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 b3db bandwidth of 70 MHz for a

gain of a1, 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.

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 in-

creased.

For additional space savings, the LM4040 precision voltage

reference is available in a tiny SOT23-3 package.

Video Gain of a2

The design of the LM7131 has been optimized for gain of

a2 video applications. Typical values for differential gain

and phase are 0.25% differential gain and 0.75 degree dif-

ferential 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 af-

fecting the video quality. If it is possible to AC couple the

signal and shift the output voltage slightly higher, much bet-

ter video performance is possible. For a a5V single supply,

an output range between 2.0V and 3.0V can have a differen-

tial gain of 0.07% and differential phase of 0.3 degree when

driving a 150Xload. For a a3V single supply, the output

should be between 1.0V and 2.0V.

Cable Driving with a5V Supplies

The LM7131 can easily drive a back-terminated 75Xvideo

cable (150Xload) when powered by a a5V supply. See

Figures 2

and

. This makes it a good choice for video

output for portable equipment, personal digital devices, and

desktop video applications.

The LM7131 can also supply a2.00V to a 50Xload to

ground, making it useful as driver in 50Xsystems such as

portable test equipment.

Cable Driving with a3V Supplies

The LM7131 can drive 150Xto 2.00V when supplied by a

3V supply. This 3V performance means that the LM7131 is

useful in battery powered video applications, such as cam-

corders, portable video mixers, still video cameras, and por-

table scanners.

TL/H/12313–23

FIGURE 15. CCD Amplifier

Using the LM7131 (Continued)

Audio and High Frequency Signal Processing

The LM7131 is useful for high fidelity audio and signal pro-

cessing. A typical LM7131 is capable of driving 2V across

150X(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 a5V Single Supply Power

Many analog systems which must work on a single a5V

supply use a ‘virtual ground’ - a reference voltage for the

signal processing which is usually between a5V and 0V.

This virtual ground is usually halfway between the top and

bottom supply rails. This is usually a2.5V for a5V systems

and a1.5V for a3V 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 lim-

its for driving a 150Xload to a virtual ground supply for

a3V and a5V. 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 a5V sys-

tems and a somewhat narrow range for a3V systems. One

way to increase this output range is to have the output load

referenced to groundÐthis 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 600Xto ground. Note that these typical numbers

are similar to those for a 150Xload. 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 fur-

ther away from the supply rails. For a a5V supply and rela-

tively high impedance load (analog-to-digital converter in-

put) the following are suggested as an initial starting range

for achieving high (l60 dB) AC accuracy

Upper output levelÐ

Approximately 0.8V to 1V below the positive (Va) rail.

Lower output levelÐ

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.

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 g2V, it may be neces-

sary to add protection diodes to the inputs. See

Figure 16

For high speed applications, it may be useful to consider low

capacitance schottky diodes. Additional feedback capaci-

tance 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 Na-

tional Semiconductor op amps is available at no charge

from your National Semiconductor representative.

TL/H/12313–24

FIGURE 16. D/A Ouput Amplifier

SOT-23-5 Tape and Reel Specification

TAPE FORMAT

Tape Section ÝCavaties Cavity Status Cover Tape Status

Leader 0 (min) Empty Sealed

(Start End) 75 (min) Empty Sealed

Carrier 3000 Filled Sealed

250 Filled Sealed

Trailer 125 (min) Empty Sealed

(Hub End) 0 (min) Empty Sealed

TAPE DIMENSIONS

TL/H/12313–25

8mm 0.130 0.124 0.130 0.126 0.138 g0.002 0.055 g0.004 0.157 0.315 g0.012

(3.3) (3.15) (3.3) (3.2) (3.5 g0.05) (1.4 g0.11) (4) (8 g0.3)

Tape Size DIM A DIM Ao DIM B DIM Bo DIM F DIM Ko DIM P1 DIM W

SOT-23-5 Tape and Reel Specification (Continued)

REEL DIMENSIONS

TL/H/12313–26

8mm 7.00 0.059 0.512 0.795 2.165 0.331 a0.059/b0.000 0.567 W1 a0.078/b0.039

330.00 1.50 13.00 20.20 55.00 8.4 a1.50/b0.00 14.40 W1 a2.00/b1.00

Tape Size A B C D N W1 W2 W3

Physical Dimensions inches (millimeters)

5-Pin SOT Package

Order Package Number LM7131ACM5*or LM7131BCM5*

NS Package Number MA05A

LM7131 Tiny High Speed Single Supply Operational Amplifier

Physical Dimensions inches (millimeters) (Continued)

8-Pin Molded DIP

8-Lead (0.300×Wide) Molded Dual-In-Line Package

Order Package Number LM7131ACN or LM7131BCN

NS Package Number N08E

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT

DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL

SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or 2. A critical component is any component of a life

systems which, (a) are intended for surgical implant support device or system whose failure to perform can

into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life

failure to perform, when properly used in accordance support device or system, or to affect its safety or

with instructions for use provided in the labeling, can effectiveness.

be reasonably expected to result in a significant injury

to the user.

National Semiconductor National Semiconductor National Semiconductor National Semiconductor National Semiconductores National Semiconductor

Corporation GmbH Japan Ltd. Hong Kong Ltd. Do Brazil Ltda. (Australia) Pty, Ltd.

2900 Semiconductor Drive Livry-Gargan-Str. 10 Sumitomo Chemical 13th Floor, Straight Block, Rue Deputado Lacorda Franco Building 16

P.O. Box 58090 D-82256 F4urstenfeldbruck Engineering Center Ocean Centre, 5 Canton Rd. 120-3A Business Park Drive

Santa Clara, CA 95052-8090 Germany Bldg. 7F Tsimshatsui, Kowloon Sao Paulo-SP Monash Business Park

Tel: 1(800) 272-9959 Tel: (81-41) 35-0 1-7-1, Nakase, Mihama-Ku Hong Kong Brazil 05418-000 Nottinghill, Melbourne

TWX: (910) 339-9240 Telex: 527649 Chiba-City, Tel: (852) 2737-1600 Tel: (55-11) 212-5066 Victoria 3168 Australia

Fax: (81-41) 35-1 Ciba Prefecture 261 Fax: (852) 2736-9960 Telex: 391-1131931 NSBR BR Tel: (3) 558-9999

Tel: (043) 299-2300 Fax: (55-11) 212-1181 Fax: (3) 558-9998

Fax: (043) 299-2500

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.