TL/H/6976
LM386 Low Voltage Audio Power Amplifier
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.
Features
YBattery operation
YMinimum external parts
YWide supply voltage range 4V–12V or 5V–18V
YLow quiescent current drain 4 mA
YVoltage gains from 20 to 200
YGround referenced input
YSelf-centering output quiescent voltage
YLow distortion
YEight pin dual-in-line package
Applications
YAM-FM radio amplifiers
YPortable tape player amplifiers
YIntercoms
YTV sound systems
YLine drivers
YUltrasonic drivers
YSmall servo drivers
YPower converters
Equivalent Schematic and Connection Diagrams
TL/H/6976–1
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
Typical Applications
Amplifier with Gain e20
Minimum Parts
TL/H/6976– 3
Amplifier with Gain e200
TL/H/6976– 4
C1995 National Semiconductor Corporation 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) 15V
Supply Voltage (LM386N-4) 22V
Package Dissipation (Note 1) (LM386N) 1.25W
(LM386M) 0.73W
Input Voltage g0.4V
Storage Temperature b65§Ctoa
150§C
Operating Temperature 0§Ctoa
70§C
Junction Temperature a150§C
Soldering Information
Dual-In-Line Package
Soldering (10 sec) a260§C
Small Outline Package
Vapor Phase (60 sec) a215§C
Infrared (15 sec) a220§C
See AN-450 ‘‘Surface Mounting Methods and Their Effect
on Product Reliability’’ for other methods of soldering sur-
face mount devices.
Thermal Resistance
iJC (DIP) 37§C/W
iJA (DIP) 107§C/W
iJC (SO Package) 35§C/W
iJA (SO Package) 172§C/W
Electrical Characteristics TAe25§C
Parameter Conditions Min Typ Max Units
Operating Supply Voltage (VS)
LM386N-1, -3, LM386M-1 4 12 V
LM386N-4 518V
Quiescent Current (IQ)V
S
e
6V, VIN e048mA
Output Power (POUT)
LM386N-1, LM386M-1 VSe6V, RLe8X, THD e10% 250 325 mW
LM386N-3 VSe9V, RLe8X, THD e10% 500 700 mW
LM386N-4 VSe16V, RLe32X, THD e10% 700 1000 mW
Voltage Gain (AV)V
S
e
6V, f e1 kHz 26 dB
10 mF from Pin 1 to 8 46 dB
Bandwidth (BW) VSe6V, Pins 1 and 8 Open 300 kHz
Total Harmonic Distortion (THD) VSe6V, RLe8X,P
OUT e125 mW 0.2 %
fe1 kHz, Pins 1 and 8 Open
Power Supply Rejection Ratio (PSRR) VSe6V, f e1 kHz, CBYPASS e10 mF50 dB
Pins 1 and 8 Open, Referred to Output
Input Resistance (RIN) 50 kX
Input Bias Current (IBIAS)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 kXresistor sets the gain at 20 (26 dB). If a capaci-
tor is put from pin 1 to 8, bypassing the 1.35 kXresistor, 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 kXresis-
tor). For 6 dB effective bass boost: R j15 kX, the lowest
value for good stable operation is R e10 kXif pin 8 is
open. If pins 1 and 8 are bypassed then R as low as 2 kX
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
witha50kXresistor. 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 kXit 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 kX, 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 kXresistor 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 mF capaci-
tor or a short to ground depending on the dc source resist-
ance on the driven input.
2
Typical Performance Characteristics
vs Supply Voltage
Quiescent Supply Current
vs Frequency
(Referred to the Output)
Power Supply Rejection Ratio
Swing vs Supply Voltage
Peak-to-Peak Output Voltage
Voltage Gain vs Frequency Distortion vs Frequency Distortion vs Output Power
PowerÐ4XLoad
Device Dissipation vs Output
PowerÐ8XLoad
Device Dissipation vs Output
PowerÐ16XLoad
Device Dissipation vs Output
TL/H/6976– 5
3
Typical Applications (Continued)
Amplifier with Gain e50
TL/H/6976– 6
Low Distortion Power Wienbridge Oscillator
TL/H/6976– 7
Amplifier with Bass Boost
TL/H/6976– 8
Square Wave Oscillator
TL/H/6976– 9
Frequency Response with Bass Boost
TL/H/6976– 10
4
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
5
LM386 Low Voltage Audio Power Amplifier
Physical Dimensions inches (millimeters) (Continued)
Dual-In-Line Package (N)
Order Number LM386N-1, LM386N-3 or LM386N-4
NS Package Number N08E
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be reasonably expected to result in a significant injury
to the user.
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