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LMV321/LMV358/LMV324Single/Dual/Quad

General Purpose,Low Voltage,Rail-to-Rail Output Operational Amplifiers

General Description

The LMV358/324are low voltage (2.7–5.5V)versions of the dual and quad commodity op amps,LM358/324,which cur-rently operate at 5–30V.The LMV321is the single version.The LMV321/358/324are the most cost effective solutions for the applications where low voltage operation,space sav-ing and low price are needed.They offer specifications that meet or exceed the familiar LM358/324.The LMV321/358/324have rail-to-rail output swing capability and the input common-mode voltage range includes ground.They all ex-hibit excellent speed-power ratio,achieving 1MHz of band-width and 1V/μs of slew rate with low supply current.

The LMV321is available in space saving SC70-5,which is approximately half the size of SOT23-5.The small package saves space on pc boards,and enables the design of small portable electronic devices.It also allows the designer to place the device closer to the signal source to reduce noise pickup and increase signal integrity.

The chips are built with National’s advanced submicron silicon-gate BiCMOS process.The LMV321/358/324have bipolar input and output stages for improved noise perfor-mance and higher output current drive.

Features

(For V +=5V and V ?=0V,Typical Unless Otherwise Noted)n Guaranteed 2.7V and 5V Performance n No Crossover Distortion n Space Saving Package SC70-52.0x2.1x1.0mm n Industrial Temp.Range ?40?C to +85?C n Gain-Bandwidth Product 1MHz n Low Supply Current —LMV321130μA —LMV358210μA —LMV324410μA

n Rail-to-Rail Output Swing @10k ?V +

?10mV

V ?+65mV

n V CM ?0.2V to V +?0.8V

Applications

n Active Filters

n General Purpose Low Voltage Applications n General Purpose Portable Devices

Gain and Phase vs.Capacitive Load 10006045Output Voltage Swing vs.Supply Voltage

10006067

June 2003

LMV321/LMV358/LMV324Single/Dual/Quad General Purpose,Low Voltage,Rail-to-Rail Output Operational Amplifiers

?2003National Semiconductor Corporation https://www.wendangku.net/doc/fe11902525.html,

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)Machine Model 100V Human Body Model LMV358/3242000V LMV321

900V

Differential Input Voltage ±Supply Voltage

Supply Voltage (V +–V ?) 5.5V Output Short Circuit to V +(Note 3)Output Short Circuit to V ?

(Note 4)

Soldering Information

Infrared or Convection (20sec)

235?C

Storage Temp.Range ?65?C to 150?C

Junction Temperature(Note 5)

150?C

Operating Ratings (Note 1)

Supply Voltage 2.7V to 5.5V Temperature Range

LMV321,LMV358,LMV324?40?C to +85?C

Thermal Resistance (θJA )(Note

10)

5-pin SC70-5478?C/W 5-pin SOT23-5265?C/W 8-Pin SOIC 190?C/W 8-Pin MSOP 235?C/W 14-Pin SOIC 145?C/W 14-Pin TSSOP

155?C/W

2.7V DC Electrical Characteristics

Unless otherwise specified,all limits guaranteed for T J

=25?C,V +=2.7V,V ?=0V,V CM =1.0V,V O =V +/2and R L >1M ?.

Symbol Parameter

Conditions

Typ (Note 6)Limit (Note 7)

Units V OS Input Offset Voltage

1.77

mV max TCV OS Input Offset Voltage Average Drift

5μV/?C I B Input Bias Current 11250nA max I OS Input Offset Current

550nA max CMRR Common Mode Rejection Ratio 0V ≤V CM ≤1.7V 6350dB min PSRR Power Supply Rejection Ratio 2.7V ≤V +≤5V V O =1V 6050dB min V CM

Input Common-Mode Voltage Range

For CMRR ≥50dB

?0.20V min 1.9

1.7V max V O

Output Swing

R L =10k ?to 1.35V

V +-10V +-100mV min 60

180mV max I S

Supply Current LMV32180170μA max LMV358

Both amplifiers 140340μA max LMV324

All four amplifiers

260

680μA max

L M V 321/L M V 358/L M V 324S i n g l e /D u a l /Q u a d

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2.7V AC Electrical Characteristics

Unless otherwise specified,all limits guaranteed for T J

=25?C,V +=2.7V,V ?=0V,V CM =1.0V,V O =V +/2and R L >1M ?.

Symbol Parameter

Conditions

Typ (Note 6)

Limit (Note 7)

Units GBWP Gain-Bandwidth Product C L =200pF

1MHz Φm Phase Margin 60Deg G m Gain Margin

10dB

e n Input-Referred Voltage Noise

f =1kHz 46i n

Input-Referred Current Noise

f =1kHz

0.17

5V DC Electrical Characteristics

Unless otherwise specified,all limits guaranteed for T J

=25?C,V +=5V,V ?=0V,V CM =2.0V,V O =V +/2and R

>1M ?.

Boldface limits apply at the temperature extremes.Symbol Parameter

Conditions Typ (Note 6)Limit (Note 7)

Units V OS Input Offset Voltage

1.779

mV max TCV OS Input Offset Voltage Average Drift

5μV/?C I B Input Bias Current 15250500nA max I OS Input Offset Current

550150nA max CMRR Common Mode Rejection Ratio 0V ≤V CM ≤4V 6550dB min PSRR Power Supply Rejection Ratio 2.7V ≤V +≤5V V O =1V V CM =1V 6050dB min V CM

Input Common-Mode Voltage Range

For CMRR ≥50dB

?0.20V min 4.2

4V max A V Large Signal Voltage Gain (Note 8)

R L =2k ?1001510V/mV min V O

Output Swing

R L =2k ?to 2.5V

V +-40V +-300V +-400mV min 120

300400mV max R L =10k ?to 2.5V

V +-10V +-100V +-200mV min 65

180280mV max I O

Output Short Circuit Current

Sourcing,V O =0V 605m min Sinking,V O =5V

16010mA min I S

Supply Current LMV321130250350μA max LMV358

Both amplifiers 210440615μA max LMV324

All four amplifiers

410

8301160μA max

LMV321/LMV358/LMV324Single/Dual/Quad

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5V AC Electrical Characteristics

Unless otherwise specified,all limits guaranteed for T J

=25?C,V +=5V,V ?=0V,V CM =2.0V,V O =V +/2and R

>1M ?.

Boldface limits apply at the temperature extremes.Symbol Parameter

Conditions

Typ (Note 6)

Limit (Note 7)

Units SR Slew Rate

(Note 9)1V/μs GBWP Gain-Bandwidth Product C L =200pF

1MHz Φm Phase Margin 60Deg G m Gain Margin

10dB

e n Input-Referred Voltage Noise

f =1kHz 39i n

Input-Referred Current Noise

f =1kHz

0.21

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,1.5k ?in series with 100pF.Machine model,0?in series with 200pF.Note 3:Shorting output to V +will adversely affect reliability.Note 4:Shorting output to V -will adversely affect reliability.

Note 5:The maximum power dissipation is a function of T J(MAX),θJA ,and T A .The maximum allowable power dissipation at any ambient temperature is P D =(T J(MAX)–T A )/θJA .All numbers apply for packages soldered directly into a PC board.Note 6:Typical values represent the most likely parametric norm.Note 7:All limits are guaranteed by testing or statistical analysis.

Note 8:R L is connected to V -.The output voltage is 0.5V ≤V O ≤4.5V.

Note 9:Connected as voltage follower with 3V step input.Number specified is the slower of the positive and negative slew rates.Note 10:All numbers are typical,and apply for packages soldered directly onto a PC board in still air.

L M V 321/L M V 358/L M V 324S i n g l e /D u a l /Q u a d

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Typical Performance Characteristics

Unless otherwise specified,V S =+5V,single supply,

T A =25?C.

Supply Current vs.Supply Voltage (LMV321)

Input Current vs.Temperature

10006073100060A9

Sourcing Current vs.Output Voltage Sourcing Current vs.Output Voltage

1000606910006068

Sinking Current vs.Output Voltage Sinking Current vs.Output Voltage

1000607010006071

LMV321/LMV358/LMV324Single/Dual/Quad

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Typical Performance Characteristics Unless otherwise specified,V S =+5V,single supply,

T A =25?C.(Continued)

Output Voltage Swing vs.Supply Voltage

Input Voltage Noise vs.Frequency

1000606710006056

Input Current Noise vs.Frequency Input Current Noise vs.Frequency

1000606010006058

Crosstalk Rejection vs.Frequency PSRR vs.Frequency

1000606110006051

L M V 321/L M V 358/L M V 324S i n g l e /D u a l /Q u a d

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Typical Performance Characteristics Unless otherwise specified,V S =+5V,single supply,

T A =25?C.(Continued)

CMRR vs.Frequency

CMRR vs.Input Common Mode Voltage

10006062

10006064

CMRR vs.Input Common Mode Voltage

?V OS vs.CMR

10006063

10006053

vs.CMR Input Voltage vs.Output Voltage

10006050

10006054

LMV321/LMV358/LMV324Single/Dual/Quad

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Typical Performance Characteristics Unless otherwise specified,V S =+5V,single supply,

T A =25?C.(Continued)

Input Voltage vs.Output Voltage

Open Loop Frequency Response

10006052

10006042

Open Loop Frequency Response Open Loop Frequency Response vs.Temperature

1000604110006043

Gain and Phase vs.Capacitive Load Gain and Phase vs.Capacitive Load

1000604510006044

L M V 321/L M V 358/L M V 324S i n g l e /D u a l /Q u a d

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Typical Performance Characteristics Unless otherwise specified,V S =+5V,single supply,

T A =25?C.(Continued)

Slew Rate vs.Supply Voltage

Non-Inverting Large Signal Pulse Response

10006057

10006088

Non-Inverting Large Signal Pulse Response Non-Inverting Large Signal Pulse Response

100060A1100060A0

Non-Inverting Small Signal Pulse Response Non-Inverting Small Signal Pulse Response

10006089100060A2

LMV321/LMV358/LMV324Single/Dual/Quad

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Typical Performance Characteristics Unless otherwise specified,V S =+5V,single supply,

T A =25?C.(Continued)

Non-Inverting Small Signal Pulse Response

Inverting Large Signal Pulse Response

100060A310006090

Inverting Large Signal Pulse Response Inverting Large Signal Pulse Response

100060A4100060A5

Inverting Small Signal Pulse Response Inverting Small Signal Pulse Response

10006091100060A6

L M V 321/L M V 358/L M V 324S i n g l e /D u a l /Q u a d

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Typical Performance Characteristics Unless otherwise specified,V

=+5V,single supply,

T A=25?C.(Continued)

Inverting Small Signal Pulse Response Stability vs.Capacitive Load

100060A7

10006046 Stability vs.Capacitive Load Stability vs.Capacitive Load

1000604710006049 Stability vs.Capacitive Load THD vs.Frequency

10006048

10006059

LMV321/LMV358/LMV324

Single/Dual/Quad

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Typical Performance Characteristics Unless otherwise specified,V S =+5V,single supply,

T A =25?C.(Continued)

Open Loop Output Impedance vs.Frequency

Short Circuit Current vs.Temperature (Sinking)

10006055

10006065

Short Circuit Current vs.Temperature (Sourcing)

10006066

L M V 321/L M V 358/L M V 324S i n g l e /D u a l /Q u a d

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Application Notes

1.0BENEFITS OF THE LMV321/358/324

Size:The small footprints of the LMV321/358/324packages save space on printed circuit boards,and enable the design of smaller electronic products,such as cellular phones,pag-ers,or other portable systems.The low profile of the LMV321/358/324make them possible to use in PCMCIA type III cards.Signal Integrity

Signals can pick up noise between the signal source and the amplifier.By using a physically smaller amplifier package,the LMV321/358/324can be placed closer to the signal source,reducing noise pickup and increasing signal integrity.Simplified Board Layout

These products help you to avoid using long pc traces in your pc board layout.This means that no additional compo-nents,such as capacitors and resistors,are needed to filter out the unwanted signals due to the interference between the long pc traces.Low Supply Current

These devices will help you to maximize battery life.They are ideal for battery powered systems.

Low Supply Voltage

National provides guaranteed performance at 2.7V and 5V.These guarantees ensure operation throughout the battery lifetime.

Rail-to-Rail Output

Rail-to-rail output swing provides maximum possible dy-namic range at the output.This is particularly important when operating on low supply voltages.

Input Includes Ground

Allows direct sensing near GND in single supply operation.The differential input voltage may be larger than V +without damaging the device.Protection should be provided to pre-vent the input voltages from going negative more than ?0.3V (at 25?C).An input clamp diode with a resistor to the IC input terminal can be used.

Ease Of Use &Crossover Distortion

The LMV321/358/324offer specifications similar to the fa-miliar LM324.In addition,the new LMV321/358/324effec-tively eliminate the output crossover distortion.The scope photos in Figure 1and Figure 2compare the output swing of the LMV324and the LM324in a voltage follower configura-tion,with V S =±2.5V and R L (=2k ?)connected to GND.It is apparent that the crossover distortion has been eliminated in the new LMV324.

2.0CAPACITIVE LOAD TOLERANCE

The LMV321/358/324can directly drive 200pF in unity-gain without oscillation.The unity-gain follower is the most sensi-tive configuration to capacitive loading.Direct capacitive loading reduces the phase margin of amplifiers.The combi-nation of the amplifier’s output impedance and the capacitive load induces phase lag.This results in either an under-damped pulse response or oscillation.To drive a heavier capacitive load,circuit in Figure 3can be used.

Time (50μs/div)

O u t p u t V o l t a g e (500m V /d i v )

10006097

FIGURE 1.Output Swing of LMV324

O u t p u t V o l t a g e (500m V /d i v )

Time (50μs/div)

10006098

FIGURE 2.Output Swing of LM324

10006004

FIGURE 3.Indirectly Driving A Capacitive Load Using

Resistive Isolation

LMV321/LMV358/LMV324Single/Dual/Quad

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Application Notes(Continued)

In Figure3,the isolation resistor R ISO and the load capacitor

C L form a pole to increase stability by adding more phase

margin to the overall system.The desired performance de-

pends on the value of R ISO.The bigger the R ISO resistor

value,the more stable V OUT will be.Figure4is an output

waveform of Figure3using620?for R ISO and510pF for C L..

The circuit in Figure5is an improvement to the one in Figure

3because it provides DC accuracy as well as AC stability.If

there were a load resistor in Figure3,the output would be

voltage divided by R ISO and the load resistor.Instead,in

Figure5,R F provides the DC accuracy by using feed-

forward techniques to connect V IN to R L.Caution is needed

in choosing the value of R F due to the input bias current of

the LMV321/358/324.C F and R ISO serve to counteract the

loss of phase margin by feeding the high frequency compo-

nent of the output signal back to the amplifier’s inverting

input,thereby preserving phase margin in the overall feed-

back loop.Increased capacitive drive is possible by increas-

ing the value of C F.This in turn will slow down the pulse

response.

3.0INPUT BIAS CURRENT CANCELLATION

The LMV321/358/324family has a bipolar input stage.The

typical input bias current of LMV321/358/324is15nA with5V

supply.Thus a100k?input resistor will cause1.5mV of error

voltage.By balancing the resistor values at both inverting

and non-inverting inputs,the error caused by the amplifier’s

input bias current will be reduced.The circuit in Figure6

shows how to cancel the error caused by input bias current.

4.0TYPICAL SINGLE-SUPPLY APPLICATION CIRCUITS

4.1Difference Amplifier

The difference amplifier allows the subtraction of two volt-

ages or,as a special case,the cancellation of a signal

common to two inputs.It is useful as a computational ampli-

fier,in making a differential to single-ended conversion or in

rejecting a common mode signal.

4.2Instrumentation Circuits

The input impedance of the previous difference amplifier is

set by the resistors R1,R2,R3,and R4.To eliminate the

problems of low input impedance,one way is to use a

voltage follower ahead of each input as shown in the follow-

ing two instrumentation amplifiers.

Time (2μs/div)

(

)

10006099

FIGURE4.Pulse Response of the LMV324Circuit in

Figure3

10006005

FIGURE5.Indirectly Driving A Capacitive Load with

DC Accuracy

10006006

FIGURE6.Cancelling the Error Caused by Input Bias

Current

10006007

10006019

FIGURE7.Difference Amplifier

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Application Notes(Continued)

4.2.1Three-Op-Amp Instrumentation Amplifier

The quad LMV324can be used to build a three-op-amp

instrumentation amplifier as shown in Figure8.

The first stage of this instrumentation amplifier is a

differential-input,differential-output amplifier,with two volt-

age followers.These two voltage followers assure that the

input impedance is over100M?.The gain of this instrumen-

tation amplifier is set by the ratio of R2/R1.R3should equal

R1,and R4equal R2.Matching of R3to R1and R4to R2

affects the CMRR.For good CMRR over temperature,low

drift resistors should be used.Making R4slightly smaller

than R2and adding a trim pot equal to twice the difference

between R2and R4will allow the CMRR to be adjusted for

optimum.

4.2.2Two-op-amp Instrumentation Amplifier

A two-op-amp instrumentation amplifier can also be used to

make a high-input-impedance dc differential amplifier(Fig-

ure9).As in the three-op-amp circuit,this instrumentation

amplifier requires precise resistor matching for good CMRR.

R4should equal to R1and R3should equal R2.

4.3Single-Supply Inverting Amplifier

There may be cases where the input signal going into the

amplifier is negative.Because the amplifier is operating in

single supply voltage,a voltage divider using R3and R4is

implemented to bias the amplifier so the input signal is within

the input common-mode voltage range of the amplifier.The

capacitor C1is placed between the inverting input and resis-

tor R1to block the DC signal going into the AC signal source,

V IN.The values of R1and C1affect the cutoff frequency,fc=

1/2πR1C1.

As a result,the output signal is centered around mid-supply

(if the voltage divider provides V+/2at the non-inverting

input).The output can swing to both rails,maximizing the

signal-to-noise ratio in a low voltage system.

4.4ACTIVE FILTER

4.4.1Simple Low-Pass Active Filter

The simple low-pass filter is shown in Figure11.Its low-

frequency gain(ω→0)is defined by-R3/R1.This allows

low-frequency gains other than unity to be obtained.The

filter has a-20dB/decade roll-off after its corner frequency fc.

R2should be chosen equal to the parallel combination of R1

and R3to minimize errors due to bias current.The frequency

response of the filter is shown in Figure12.

10006085

FIGURE8.Three-op-amp Instrumentation Amplifier

10006011

10006035

FIGURE9.Two-Op-amp Instrumentation Amplifier

10006013

10006020

FIGURE10.Single-Supply Inverting Amplifier

LMV321/LMV358/LMV324

Single/Dual/Quad

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Application Notes(Continued)

Note that the single-op-amp active filters are used in to the

applications that require low quality factor,Q(≤10),low

frequency(≤5kHz),and low gain(≤10),or a small value for

the product of gain times Q(≤100).The op amp should have

an open loop voltage gain at the highest frequency of inter-

est at least50times larger than the gain of the filter at this

frequency.In addition,the selected op amp should have a

slew rate that meets the following requirement:

Slew Rate≥0.5x(ωH V OPP)x10?6V/μsec

whereωH is the highest frequency of interest,and V opp is the

output peak-to-peak voltage.

4.4.2Sallen-Key2nd-Order Active Low-Pass Filter

The Sallen-Key2nd-order active low-pass filter is illustrated

in Figure13.The dc gain of the filter is expressed as

(1)

Its transfer function is

(2)

The following paragraphs explain how to select values for

R1,R2,R3,R4,C1,and C2for given filter requirements,such

as A LP,Q,and f c.

The standard form for a2nd-order low pass filter is

(3)

where

Q:Pole Quality Factor

ωC:Corner Frequency

Comparison between the Equation(2)and Equation(3)

yields

(4)

(5)

To reduce the required calculations in filter design,it is

convenient to introduce normalization into the components

and design parameters.To normalize,letωC=ωn=1rad/s,

and C1=C2=C n=1F,and substitute these values into

Equation(4)and Equation(5).From Equation(4),we obtain

(6)

From Equation(5),we obtain

(7)

10006014

10006037

FIGURE11.Simple Low-Pass Active Filter

10006015

FIGURE12.Frequency Response of Simple Low-Pass

Active Filter in Figure11

10006016

FIGURE13.Sallen-Key2nd-Order Active Low-Pass

Filter

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Application Notes(Continued)

For minimum dc offset,V+=V?,the resistor values at both

inverting and non-inverting inputs should be equal,which

means

(8)

From Equation(1)and Equation(8),we obtain

(9)

(10)

The values of C1and C2are normally close to or equal to

As a design example:

Require:A LP=2,Q=1,fc=1KHz

Start by selecting C1and C2.Choose a standard value that

is close to

From Equations(6),(7),(9),(10),

R1=1?

R2=1?

R3=4?

R4=4?

The above resistor values are normalized values withωn=

1rad/s and C1=C2=C n=1F.To scale the normalized cut-off

frequency and resistances to the real values,two scaling

factors are introduced,frequency scaling factor(k f)and im-

pedance scaling factor(k m).

Scaled values:

R2=R1=15.9k?

R3=R4=63.6k?

C1=C2=0.01μF

An adjustment to the scaling may be made in order to have

realistic values for resistors and capacitors.The actual value

used for each component is shown in the circuit.

4.4.32nd-order High Pass Filter

A2nd-order high pass filter can be built by simply inter-

changing those frequency selective components(R1,R2,

C1,C2)in the Sallen-Key2nd-order active low pass filter.As

shown in Figure14,resistors become capacitors,and ca-

pacitors become resistors.The resulted high pass filter has

the same corner frequency and the same maximum gain as

the previous2nd-order low pass filter if the same compo-

nents are chosen.

4.4.4State Variable Filter

A state variable filter requires three op amps.One conve-

nient way to build state variable filters is with a quad op amp,

such as the LMV324(Figure15).

This circuit can simultaneously represent a low-pass filter,

high-pass filter,and bandpass filter at three different outputs.

The equations for these functions are listed below.It is also

called"Bi-Quad"active filter as it can produce a transfer

function which is quadratic in both numerator and

denominator.

10006083

FIGURE14.Sallen-Key2nd-Order Active High-Pass

Filter

LMV321/LMV358/LMV324

Single/Dual/Quad

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Application Notes(Continued)

where for all three filters,

(11)

(12)

A design example for a bandpass filter is shown below:

Assume the system design requires a bandpass filter with f O

=1kHz and Q=50.What needs to be calculated are

capacitor and resistor values.

First choose convenient values for C1,R1and R2:

C1=1200pF

2R2=R1=30k?

Then from Equation(11),

From Equation(12),

From the above calculated values,the midband gain is H0=

R3/R2=100(40dB).The nearest5%standard values have

been added to Figure15.

4.5PULSE GENERATORS AND OSCILLATORS

A pulse generator is shown in Figure16.Two diodes have

been used to separate the charge and discharge paths to

capacitor C.

10006039

FIGURE15.State Variable Active Filter

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Application Notes

(Continued)

When the output voltage V O is first at its high,V OH ,the capacitor C is charged toward V OH through R 2.The voltage across C rises exponentially with a time constant τ=R 2C,and this voltage is applied to the inverting input of the op amp.Meanwhile,the voltage at the non-inverting input is set at the positive threshold voltage (V TH+)of the generator.The capacitor voltage continually increases until it reaches V TH+,at which point the output of the generator will switch to its low,V OL (=0V in this case).The voltage at the non-inverting input is switched to the negative threshold voltage (V TH-)of the generator.The capacitor then starts to discharge toward V OL exponentially through R 1,with a time constant τ=R 1C.When the capacitor voltage reaches V TH-,the output of the pulse generator switches to V OH .The capacitor starts to charge,and the cycle repeats itself.

As shown in the waveforms in Figure 17,the pulse width (T 1)is set by R 2,C and V OH ,and the time between pulses (T 2)is set by R 1,C and V OL .This pulse generator can be made to have different frequencies and pulse width by selecting dif-ferent capacitor value and resistor values.

Figure 18shows another pulse generator,with separate charge and discharge paths.The capacitor is charged through R 1and is discharged through R 2.

Figure 19is a squarewave generator with the same path for charging and discharging the capacitor.

10006081

FIGURE 16.Pulse Generator

10006086

FIGURE 17.Waveforms of the Circuit in Figure 1610006077

FIGURE 18.Pulse Generator

LMV321/LMV358/LMV324Single/Dual/Quad

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Application Notes(Continued)

4.6CURRENT SOURCE AND SINK

The LMV321/358/324can be used in feedback loops which

regulate the current in external PNP transistors to provide

current sources or in external NPN transistors to provide

current sinks.

4.6.1Fixed Current Source

A multiple fixed current source is show in Figure20.A

voltage(V REF=2V)is established across resistor R3by the

voltage divider(R3and R4).Negative feedback is used to

cause the voltage drop across R1to be equal to V REF.This

controls the emitter current of transistor Q1and if we neglect

the base current of Q1and Q2,essentially this same current

is available out of the collector of Q1.

Large input resistors can be used to reduce current loss and

a Darlington connection can be used to reduce errors due to

theβof Q1.

The resistor,R2,can be used to scale the collector current of

Q2either above or below the1mA reference value.

4.6.2High Compliance Current Sink

A current sink circuit is shown in Figure21.The circuit

requires only one resistor(R E)and supplies an output cur-

rent which is directly proportional to this resistor value.

4.7POWER AMPLIFIER

A power amplifier is illustrated in Figure22.This circuit can

provide a higher output current because a transistor follower

is added to the output of the op amp.

4.8LED DRIVER

The LMV321/358/324can be used to drive an LED as shown

in Figure23.

10006076

FIGURE19.Squarewave Generator

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FIGURE20.Fixed Current Source

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FIGURE21.High Compliance Current Sink

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FIGURE22.Power Amplifier

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FIGURE23.LED Driver

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