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TLH7919

LM1895LM

2895AudioPowerAmplifier

July 1987

LM1895LM2895 Audio Power Amplifier

General DescriptionThe LM1895 is a 6V audio power amplifier designed to de-liver 1W into 4X Utilizing a unique patented compensation

scheme the LM1895 is ideal for sensitive AM radio applica-tions This new circuit technique exhibits lower noise lowerdistortion and less AM radiation than conventional designs

The amplifiers supply range (3V9V) is ideal for battery op-eration The LM1895 is packaged in an 8-pin miniDIP for

minimum PC board space For higher supplies (VS l 9V)the LM2895 is available in an 11-lead single-in-line package

The 11-lead package has been redesigned resulting in aslightly degraded thermal characteristic shown in the figureDevice Dissipation vs Ambient Temperature

FeaturesY Guaranteed low crossover distortionY Low AM radiation

Y Low noiseY 3V 4X PO e 250 mWY Wide supply operation 3V 15V (LM2895)Y Low distortionY No turn on popY Smooth waveform clippingY 8-pin miniDIP (LM1895)Y 12V 4X PO e 4W (LM2895)Y Tested for low crossover distortion

ApplicationsY Compact AM-FM radiosY Battery operated tape player amplifiersY Line driver

Typical Applications

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FIGURE 1 LM1895 with AV e 500 BW e 5 kHz AM Radio

Application (VIN e 42 mV for Full Power Output)

Order Number LM1895N or LM2895P

See NS Package Number N08E or P11A

C1995 National Semiconductor Corporation RRD-B30M115Printed in U S A

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Absolute Maximum RatingsIf MilitaryAerospace specified devices are required

please contact the National Semiconductor Sales

OfficeDistributors for availability and specifications

Supply VoltageLM1895 VS e 12V

LM2895 VS e 18V

Operating Temperature (Note 1) 0C to a70C

Storage Temperature b65C to a150C

Junction Temperature 150C

Lead Temperat ure ( Sol dering 10 sec) 260C

Electrical CharacteristicsUnless otherwise specified TA e 25C AV e 200 (46 dB) For the LM1895 VS e 6V and RL e 4X For the LM2895 TTAB e

25C VS e12V and RL e 4X Test circuit shown in Figure 2

Parameter Conditions LM1895 LM2895

UnitsMi n Typ Max Min Typ Max

Supply Current PO e W 8 14 12 20 mA

Operating Supply Voltage 3 10 3 15 V

Output Power THD e 10% f e 1 kHz

LM1895N VS e 6V RL e 4X TA e 25C 09 11 W

VS e 9V RL e 8X( 11 WLM2895P VS e 12V RL e 4X TTAB e 25C

36 43 W

VS e 12V RL e 8X( 25 WDistortion f e 1 kHz

POe

50 mW 027 027 %PO e 05W 020 020 %

PO e 10W 015 %

f e 20 kHz PO e 100 mW VS e 36V 30 30 %

Crossover Distort ion f e 20 kHz RL e 4X PO e 100 mW 3 3 %VCC e 36V

Power Supply Rejection CBY e 100 mF f e 1 kHz CIN e 01 mF 40 52 40 52 dBRatio (PSRR) Output Referred VRIPPLE e 250 mV

Noise Equivalent Input Noise RS e 0

CIN e 01 mF BW e 20 b20 kHz 14 14 mV

CCIRARM 14 14 mV

Wideband 20 20 mV

DC Output Level 28 30 32 56 60 64 V

Input Impedance 50 150 350 50 150 350 kX

Input Offset Voltage 5 5 mV

Input Bias Current 120 120 nA

Note 1For operation at ambient temperature greater than 25 C the LM1895LM2895 must be derated based on a maximum junction temperature using a thermalresistance which depends upon mounting techniques

Typical Performance Characteristics

vs Ambient Temperature

LM2895 Device Dissipation

Temperature

Dissipation vs Ambient

LM1895 Maximum Device

Operation

Voltage Gain for Stable

b3 dB Bandwidth vs

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Typical Performance Characteristics (Continued)

Speaker Lead Placement

vs Field Strength for Different

AM Recovered Audio and Noise

AV e 54 dB BW e 30 kHz

THD and Gain vs Frequency

AV e 54 dB BW e 5 kHz

THD and Gain vs Frequency

AV e 46 dB BW e 30 kHz

THD and Gain vs Frequency

AV e 40 dB BW e 20 kHz

THD and Gain vs Frequency

AV e 34 dB BW e 50 kHz

THD and Gain vs Frequency

Output) vs Frequency

Ratio (Referred to the

Power Supply Rejection

Voltage

Power Output vs Supply

vs Output Power

Total Harmonic Distortion

Output Power RL e 8X

Power Dissipation vs

Output Power RL e 4X

Power Dissipation vs

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Equivalent Schematic

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Pin 7 no connection on LM1895

Pins 4 7 10 11 no connection on LM2895

( ) indicates pin number for LM2895

Typical Applications (Continued)

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FIGURE 2 Amplifier with AV e 200 BW e 30 kHz

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External Components (Figure 2)Components Comments

1 R1 R5 Sets voltage gain AV e 1 a R1R5

2 R2 Bootstrap resistor sets drive current for output stage and allows pin 2 to go

above VS3 RO Works with COto stabilize output stage

4 C4 Input coupling capacitor Pin 4 is at a DC potential of VS2 Low frequencypole set by

fL e1

2q RINC45 C5 Feedback capacitor Ensure unity gain at DC Also a low frequency pole at

fL e1

2q R5C56 C2 Bootstrap capacitor used to increase drive to output stage A low frequency

pole is set by

fL e1

2q R2C27 C1 Compensation capacitor This stabilizes the amplifier and adjusts the

bandwidth See curve of bandwidth vs allowable gain

8 C3 Improves power supply rejection (See Typical Performance Curves)Increasing C3 increases turn-on delay

9 CC Output coupling capacitor Isolates pin 1 from the load Low frequency poleset by

fL e 12q CCRL

10 CO Works with ROto stabilize output stage

11 CS Provides power supply filtering

Connection Diagrams

Dual-In-Line Package

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Top View

Single-In-Line Package

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Top View

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Application HintsAM Radios

The LM1895LM2895 have been designed to fill a widerange of audio power applications A common problem withIC audio power amplifiers has been poor signal-to-noise per-

formance when used in AM radio applications In a typicalradio application the loopstick antenna is in close proximity

to the audio amplifier Current flowing in the speaker andpower supply leads can cause electromagnetic coupling tothe loopstick resulting in system oscillation In addition

most audio power amplifiers are not optimized for lowestnoise because of compensation requirements If noise from

the audio amplifier radiates into the AM section the sensitiv-ity and signal-to-noise ratio will be degraded

The LM1895 exhibits extremely low wideband noise due in

part to an external capacitor C1 which is used to tailor thebandwidth The circuit shown inFigure 2 is capable of asignal-to-noise ratio in excess of 60 dB referred to 50 mW

Capacitor C1 not only limits the closed loop bandwidth italso provides overall loop compensation Neglecting C5 in

Figure 2 the gain is

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FIGURE 3 Improved AM Sensitivity

Over Conventional Design

AV(S) eS a AV0o

S a 0o

where AV eR1 aR5

R5 0o e

1

R1C1

A curve of b3 dB BW (0o) vs AV is shown in the Typical

Performance CurvesFigure 3shows a plot of recovered audio as a function offield strength inmVM The receiver section in this example

is an LM3820 The power amplifier is located about twoinches from the loopstick antenna Speaker leads run paral-lel to the loopstick and are 18 inch from it Referenced to a

20 dB SN ratio the improvement in noise performanceover conventional designs is about 10 dB This corresponds

to an increase in usable sensitivity of about 85 dB

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FIGURE 4 Printed Circuit Board Layout for LM1895

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Physical Dimensions inches (millimeters)

Molded Dual-In-Line Package (N)

Order Number LM1895N

NS Package Number N08E

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LM

1895LM2895AudioPow

erAmplifier

Physical Dimensions inches (millimeters) (Continued)

Molded Single-In-Line Package (P)

Order Number LM2895P

NS Package Number P11A

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NATIONALS PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORTDEVICES 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 caninto the body or (b) support or sustain life and whose be reasonably expected to cause the failure of the lifefailure 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 effectivenessbe reasonably expected to result in a significant injury

to the user

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