LM386.pdf

September 1997

LM386

Low Voltage Audio Power Amplifier

General Description

The LM386 is a power amplifier designed for use in low volt-

age 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.

Features

n Battery operation

n Minimum external parts

n Wide supply voltage range: 4V–12V or 5V–18V

n Low quiescent current drain: 4 mA

n Voltage gains from 20 to 200

n Ground referenced input

n Self-centering output quiescent voltage

n Low distortion

n Available in 8 pin MSOP package

Applications

n AM-FM radio amplifiers

n Portable tape player amplifiers

n Intercoms

n TV sound systems

n Line drivers

n Ultrasonic drivers

n Small servo drivers

n Power converters

Equivalent Schematic and Connection Diagrams

Small Outline,

Molded Mini Small Outline,

and Dual-In-Line Packages

DS006976-2

DS006976-1

Top View

Order Number LM386M-1,

LM386MM-1, LM386N-1, LM386N-3

or LM386N-4

See NS Package Number

M08A, MUA08A or N08E

www.national.com

Absolute Maximum Ratings (Note 2)

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)

Dual-In-Line Package

Soldering (10 sec)

+260˚C

15V

Small Outline Package

(SOIC and MSOP)

Vapor Phase (60 sec) +215˚C

Infrared (15 sec) +220˚C

See AN-450 “Surface Mounting Methods and Their Effect

on Product Reliability” for other methods of soldering

surface mount devices.

Thermal Resistance

q JC (DIP)

Supply Voltage (LM386N-4)

22V

Package Dissipation (Note 3)

(LM386N)

1.25W

(LM386M)

0.73W

37˚C/W

(LM386MM-1)

0.595W

q JA (DIP)

107˚C/W

± 0.4V

Input Voltage

q JC (SO Package)

35˚C/W

Storage Temperature

−65˚C to +150˚C

q JA (SO Package)

172˚C/W

Operating Temperature

0˚C to +70˚C

q JA (MSOP)

210˚C/W

Junction Temperature

+150˚C

q JC (MSOP)

56˚C/W

Soldering Information

Electrical Characteristics(Notes 1, 2)

T A = 25˚C

Parameter

Conditions

Min Typ Max Units

Operating Supply Voltage (V S )

LM386N-1, -3, LM386M-1, LM386MM-1

LM386N-4

Quiescent Current (I Q )

V S = 6V, V IN = 0

Output Power (P OUT )

LM386N-1, LM386M-1, LM386MM-1

V S = 6V, R L = 8

, THD = 10%

250 325

LM386N-3

V S = 9V, R L = 8

, THD = 10%

500 700

LM386N-4

V S = 16V, R L = 32

, THD = 10%

700 1000

Voltage Gain (A V )

V S = 6V, f = 1 kHz

10 µF from Pin 1 to 8

Bandwidth (BW)

V S = 6V, Pins 1 and 8 Open

300

kHz

Total Harmonic Distortion (THD)

V S = 6V, R L = 8

,P OUT = 125 mW

0.2

f = 1 kHz, Pins 1 and 8 Open

Power Supply Rejection Ratio (PSRR) V S = 6V, f = 1 kHz, C BYPASS = 10 µF

Pins 1 and 8 Open, Referred to Output

Input Resistance (R IN )

Input Bias Current (I BIAS )

V S = 6V, Pins 2 and 3 Open

250

Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.

Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func-

tional, but do not guarantee specific performance limits. Electrical Characteristics state DC andAC electrical specifications under particular test conditions which guar-

antee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is

given, however, the typical value is a good indication of device performance.

Note 3: 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 resis-

tance 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.

www.national.com

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 W resistor sets the gain at 20 (26 dB). If a capacitor

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

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 W 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 W , 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 put-

ting a resistor from the unused input to ground, equal in

value to the dc source resistance. Of course all offset prob-

lems are eliminated if the input is capacitively coupled.

When using the LM386 with higher gains (bypassing the

1.35 k W resistor between pins 1 and 8) it is necessary to by-

pass the unused input, preventing degradation of gain and

possible instabilities. This is done with a 0.1 µF capacitor or

a short to ground depending on the dc source resistance on

the driven input.

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 fre-

quency 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 series

RC from pin 1 to 5 (paralleling the internal 15 k

resistor).

For 6 dB effective bass boost: R

15 k W , the lowest value

if pin 8 is open. If pins

1 and 8 are bypassed then R as low as 2 k W can be used.

This restriction is because the amplifier is only compensated

for closed-loop gains greater than 9.

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INPUT BIASING

The schematic shows that both inputs are biased to ground

witha50k

for good stable operation is R = 10 k

Typical Performance Characteristics

Quiescent Supply Current

vs Supply Voltage

Power Supply Rejection Ratio

(Referred to the Output)

vs Frequency

Peak-to-Peak Output Voltage

Swing vs Supply Voltage

DS006976-5

DS006976-13

DS006976-12

Voltage Gain vs Frequency

Distortion vs Frequency

Distortion vs Output Power

DS006976-14

DS006976-15

DS006976-16

Device Dissipation vs Output

Power— 4 W Load

Device Dissipation vs Output

Power— 8 W Load

Device Dissipation vs Output

Power— 16 W Load

DS006976-17

DS006976-18

DS006976-19

www.national.com

Typical Applications

Amplifier with Gain = 20

Minimum Parts

Amplifier with Gain = 200

DS006976-4

DS006976-3

Amplifier with Gain = 50

Low Distortion Power Wienbridge Oscillator

DS006976-6

DS006976-7

Amplifier with Bass Boost

Square Wave Oscillator

DS006976-8

DS006976-9

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