LM386
Low Voltage Audio Power Amplifier
LM386 Low Voltage Audio Power Amplifier
August 2000
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 from 20 to 200.
The inputs are ground referenced while the output automatically biases to one-half the supply voltage. The quiescent
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: 4mA
n Voltage gains from 20 to 200
n Ground referenced input
n Self-centering output quiescent voltage
n Low distortion: 0.2% (A
125mW, f = 1kHz)
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
Molded Mini Small Outline,
and Dual-In-Line Packages
= 20, VS=6V,RL=8Ω,PO=
V
Small Outline,
DS006976-2
Top View
DS006976-1
© 2000 National Semiconductor Corporation DS006976 www.national.com
Order Number LM386M-1,
LM386MM-1, LM386N-1,
LM386N-3 or LM386N-4
See NS Package Number
M08A, MUA08A or N08E
Absolute Maximum Ratings (Note 2)
LM386
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 3)
(LM386N) 1.25W
(LM386M) 0.73W
(LM386MM-1) 0.595W
Input Voltage
Storage Temperature −65˚C to +150˚C
Operating Temperature 0˚C to +70˚C
Junction Temperature +150˚C
Soldering Information
±
0.4V
Dual-In-Line Package
Soldering (10 sec) +260˚C
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
(DIP) 37˚C/W
θ
JC
(DIP) 107˚C/W
θ
JA
(SO Package) 35˚C/W
θ
JC
(SO Package) 172˚C/W
θ
JA
(MSOP) 210˚C/W
θ
JA
(MSOP) 56˚C/W
θ
JC
Electrical Characteristics (Notes 1, 2)
TA= 25˚C
Parameter Conditions Min Typ Max Units
Operating Supply Voltage (V
LM386N-1, -3, LM386M-1, LM386MM-1 4 12 V
LM386N-4 518V
Quiescent Current (I
Output Power (P
)V
Q
)
OUT
LM386N-1, LM386M-1, LM386MM-1 V
LM386N-3 V
LM386N-4 V
Voltage Gain (A
)V
V
Bandwidth (BW) V
Total Harmonic Distortion (THD) V
Power Supply Rejection Ratio (PSRR) V
Input Resistance (R
Input Bias Current (I
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 2: AbsoluteMaximum Ratings indicate limits beyond which damage to the device may occur.Operating Ratings indicate conditions for which the device is func-
tional, but donot guarantee specific performance limits. Electrical Characteristics state DC andAC electrical specifications under particular test conditions whichguarantee 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 resistance of 107˚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.
) 50 kΩ
IN
BIAS
)
S
= 6V, VIN=0 4 8 mA
S
= 6V, RL=8Ω, THD = 10% 250 325 mW
S
= 9V, RL=8Ω, THD = 10% 500 700 mW
S
= 16V, RL=32Ω, THD = 10% 700 1000 mW
S
= 6V, f = 1 kHz 26 dB
S
10 µF from Pin 1 to 8 46 dB
= 6V, Pins 1 and 8 Open 300 kHz
S
= 6V, RL=8Ω,P
S
f = 1 kHz, Pins 1 and 8 Open
= 6V, f = 1 kHz, C
S
Pins 1 and 8 Open, Referred to Output
)V
= 6V, Pins 2 and 3 Open 250 nA
S
= 125 mW 0.2 %
OUT
BYPASS
=10µF 50 dB
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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 kΩ resistor sets the gain at 20 (26 dB). If a capacitor
is put from pin 1 to 8, bypassing the 1.35 kΩ 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 coupling 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 frequency shaping the feedback path. This is done with a series
RC from pin 1 to 5 (paralleling the internal 15 kΩ resistor).
For 6 dB effective bass boost: R . 15 kΩ, the lowest value
for good stable operation is R = 10 kΩ if pin 8 is open. If pins
1 and 8 are bypassed then R as low as 2 kΩ can be used.
This restriction is because the amplifier is only compensated
for closed-loop gains greater than 9.
LM386
INPUT BIASING
The schematic shows that both inputs are biased to ground
witha50kΩresistor. 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 kΩ 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 kΩ, 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 capacitively coupled.
When using the LM386 with higher gains (bypassing the
1.35 kΩ 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 µF capacitor or
a short to ground depending on the dc source resistance on
the driven input.
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