LM386.PDF

December 1994

LM386 Low Voltage Audio Power Amplifier

General Description

The LM386 is a power amplifier designed for use in low

voltage consumer applications. The gain is internally set to

20 to keep external part count low, but the addition of an

external resistor and capacitor between pins 1 and 8 will

increase the gain to any value up to 200.

The inputs are ground referenced while the output is auto-

matically biased to one half the supply voltage. The quies-

cent power drain is only 24 milliwatts when operating from a

6 volt supply, making the LM386 ideal for battery operation.

Y Voltage gains from 20 to 200

Y Ground referenced input

Y Self-centering output quiescent voltage

Y Low distortion

Y Eight pin dual-in-line package

Applications

Y AM-FM radio amplifiers

Y Portable tape player amplifiers

Y Intercoms

Y TV sound systems

Y Line drivers

Y Ultrasonic drivers

Y Small servo drivers

Y Power converters

Features

Y Battery operation

Y Minimum external parts

Y Wide supply voltage range

4V±12V or 5V±18V

Y Low quiescent current drain

4 mA

Equivalent Schematic and Connection Diagrams

Dual-In-Line and Small Outline

Packages

TL/H/6976±2

Top View

Order Number LM386M-1,

LM386N-1, LM386N-3 or LM386N-4

See NS Package Number

M08A or N08E

TL/H/6976±1

Typical Applications

Amplifier with Gain e 20

Minimum Parts

Amplifier with Gain e 200

TL/H/6976±4

TL/H/6976±3

C 1995 National Semiconductor Corporation

TL/H/6976

RRD-B30M75/Printed in U. S. A.

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Supply Voltage (LM386N-1, -3, LM386M-1)

Soldering Information

Dual-In-Line Package

Soldering (10 sec)

a 260 § C

15V

Small Outline Package

Vapor Phase (60 sec) a 215 § C

Infrared (15 sec) a 220 § C

See AN-450 ``Surface Mounting Methods and Their Effect

on Product Reliability'' for other methods of soldering sur-

face mount devices.

Thermal Resistance

i JC (DIP)

Supply Voltage (LM386N-4)

22V

Package Dissipation (Note 1) (LM386N)

1.25W

(LM386M)

0.73W

Input Voltage

g 0.4V

Storage Temperature

b 65 § Cto a 150 § C

Operating Temperature

0 § Cto a 70 § C

37 § C/W

Junction Temperature

a 150 § C

i JA (DIP)

107 § C/W

i JC (SO Package)

35 § C/W

i JA (SO Package)

172 § C/W

Electrical Characteristics T A e 25 § C

Parameter

Conditions

Min Typ Max Units

Operating Supply Voltage (V S )

LM386N-1, -3, LM386M-1

LM386N-4

Quiescent Current (I Q )

V S e 6V, V IN e 0

8 mA

Output Power (P OUT )

LM386N-1, LM386M-1

V S e 6V, R L e 8 X , THD e 10%

250

325

LM386N-3

V S e 9V, R L e 8 X , THD e 10%

500

700

LM386N-4

V S e 16V, R L e 32 X , THD e 10% 700

1000

Voltage Gain (A V )

V S e 6V, f e 1 kHz

10 m F from Pin 1 to 8

Bandwidth (BW)

V S e 6V, Pins 1 and 8 Open

300

kHz

Total Harmonic Distortion (THD)

V S e 6V, R L e 8 X ,P OUT e 125 mW

0.2

f e 1 kHz, Pins 1 and 8 Open

Power Supply Rejection Ratio (PSRR) V S e 6V, f e 1 kHz, C BYPASS e 10 m F

Pins 1 and 8 Open, Referred to Output

Input Resistance (R IN ) 50 k X

Input Bias Current (I BIAS ) V S e 6V, Pins 2 and 3 Open 250 nA

Note 1: For operation in ambient temperatures above 25 § C, the device must be derated based on a 150 § C maximum junction temperature and 1) a thermal

resistance of 80 § C/W junction to ambient for the dual-in-line package and 2) a thermal resistance of 170 § C/W for the small outline package.

Application Hints

GAIN CONTROL

To make the LM386 a more versatile amplifier, two pins (1

and 8) are provided for gain control. With pins 1 and 8 open

the 1.35 k X resistor sets the gain at 20 (26 dB). If a capaci-

tor is put from pin 1 to 8, bypassing the 1.35 k X resistor, the

gain will go up to 200 (46 dB). If a resistor is placed in series

with the capacitor, the gain can be set to any value from 20

to 200. Gain control can also be done by capacitively cou-

pling a resistor (or FET) from pin 1 to ground.

Additional external components can be placed in parallel

with the internal feedback resistors to tailor the gain and

frequency response for individual applications. For example,

we can compensate poor speaker bass response by fre-

quency shaping the feedback path. This is done with a se-

ries RC from pin 1 to 5 (paralleling the internal 15 k X resis-

tor). For 6 dB effective bass boost: R j 15 k X , the lowest

value for good stable operation is R e 10 k X if pin 8 is

open. If pins 1 and 8 are bypassed then R as low as 2 k X

can be used. This restriction is because the amplifier is only

compensated for closed-loop gains greater than 9.

INPUT BIASING

The schematic shows that both inputs are biased to ground

witha50k X resistor. The base current of the input transis-

tors is about 250 nA, so the inputs are at about 12.5 mV

when left open. If the dc source resistance driving the

LM386 is higher than 250 k X it will contribute very little

additional offset (about 2.5 mV at the input, 50 mV at the

output). If the dc source resistance is less than 10 k X , then

shorting the unused input to ground will keep the offset low

(about 2.5 mV at the input, 50 mV at the output). For dc

source resistances between these values we can eliminate

excess offset by putting a resistor from the unused input to

ground, equal in value to the dc source resistance. Of

course all offset problems are eliminated if the input is ca-

pacitively coupled.

When using the LM386 with higher gains (bypassing the

1.35 k X resistor between pins 1 and 8) it is necessary to

bypass the unused input, preventing degradation of gain

and possible instabilities. This is done with a 0.1 m F capaci-

tor or a short to ground depending on the dc source resist-

ance on the driven input.

Typical Performance Characteristics

Power Supply Rejection Ratio

Quiescent Supply Current

(Referred to the Output)

Peak-to-Peak Output Voltage

vs Supply Voltage

vs Frequency

Swing vs Supply Voltage

Voltage Gain vs Frequency

Distortion vs Frequency

Distortion vs Output Power

Device Dissipation vs Output

PowerÐ4 X Load

PowerÐ8 X Load

PowerÐ16 X Load

TL/H/6976±5

Typical Applications (Continued)

Amplifier with Gain e 50

Low Distortion Power Wienbridge Oscillator

TL/H/6976±6

TL/H/6976±7

Amplifier with Bass Boost

Square Wave Oscillator

TL/H/6976±8

TL/H/6976±9

Frequency Response with Bass Boost

TL/H/6976±10

Typical Applications (Continued)

AM Radio Power Amplifier

TL/H/6976±11

Note 1: Twist supply lead and supply ground very tightly.

Note 2: Twist speaker lead and ground very tightly.

Note 3: Ferrite bead is Ferroxcube K5-001-001/3B with 3 turns of wire.

Note 4: R1C1 band limits input signals.

Note 5: All components must be spaced very close to IC.

Physical Dimensions inches (millimeters)

SO Package (M)

Order Number LM386M-1

NS Package Number M08A

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