LM386 Low Voltage Audio Power Amplifier

LM386 Low Voltage Audio Power Amplifier
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 automatically biased 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.
Y
Features
Y
Y
Y
Y
Y
Y
Y
Y
Y
Applications
Y
Y
Y
Battery operation
Minimum external parts
Wide supply voltage range
Low quiescent current drain
Y
Y
4V–12V or 5V – 18V
4 mA
Voltage gains from 20 to 200
Ground referenced input
Self-centering output quiescent voltage
Low distortion
Eight pin dual-in-line package
Y
Y
AM-FM radio amplifiers
Portable tape player amplifiers
Intercoms
TV sound systems
Line drivers
Ultrasonic drivers
Small servo drivers
Power converters
Equivalent Schematic and Connection Diagrams
Dual-In-Line and Small Outline
Packages
TL/H/6976 – 2
Top View
TL/H/6976 – 1
Order Number LM386M-1,
LM386N-1, LM386N-3 or LM386N-4
See NS Package Number
M08A or N08E
Typical Applications
Amplifier with Gain e 20
Minimum Parts
Amplifier with Gain e 200
TL/H/6976 – 4
TL/H/6976 – 3
C1995 National Semiconductor Corporation
TL/H/6976
RRD-B30M75/Printed in U. S. A.
LM386 Low Voltage Audio Power Amplifier
December 1994
Absolute Maximum Ratings
Soldering Information
Dual-In-Line Package
Soldering (10 sec)
Small Outline Package
Vapor Phase (60 sec)
Infrared (15 sec)
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)
Supply Voltage (LM386N-4)
Package Dissipation (Note 1) (LM386N)
(LM386M)
Input Voltage
Storage Temperature
Operating Temperature
Junction Temperature
a 260§ C
a 215§ C
a 220§ C
See AN-450 ‘‘Surface Mounting Methods and Their Effect
on Product Reliability’’ for other methods of soldering surface 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
g 0.4V
b 65§ C to a 150§ C
Electrical Characteristics
Parameter
15V
22V
1.25W
0.73W
0§ C to a 70§ C
a 150§ C
TA e 25§ C
Conditions
Operating Supply Voltage (VS)
LM386N-1, -3, LM386M-1
LM386N-4
Min
Typ
4
5
Quiescent Current (IQ)
VS e 6V, VIN e 0
Output Power (POUT)
LM386N-1, LM386M-1
LM386N-3
LM386N-4
4
VS e 6V, RL e 8X, THD e 10%
VS e 9V, RL e 8X, THD e 10%
VS e 16V, RL e 32X, THD e 10%
250
500
700
Max
Units
12
18
V
V
8
mA
325
700
1000
mW
mW
mW
Voltage Gain (AV)
VS e 6V, f e 1 kHz
10 mF from Pin 1 to 8
26
46
dB
dB
Bandwidth (BW)
VS e 6V, Pins 1 and 8 Open
300
kHz
Total Harmonic Distortion (THD)
VS e 6V, RL e 8X, POUT e 125 mW
f e 1 kHz, Pins 1 and 8 Open
0.2
%
Power Supply Rejection Ratio (PSRR)
VS e 6V, f e 1 kHz, CBYPASS e 10 mF
Pins 1 and 8 Open, Referred to Output
50
dB
50
250
kX
nA
Input Resistance (RIN)
Input Bias Current (IBIAS)
VS e 6V, Pins 2 and 3 Open
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
INPUT BIASING
The schematic shows that both inputs are biased to ground
with a 50 kX resistor. The base current of the input transistors 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 kX 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 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 capacitively coupled.
When using the LM386 with higher gains (bypassing the
1.35 kX 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 mF capacitor or a short to ground depending on the dc source resistance on the driven input.
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 kX resistor sets the gain at 20 (26 dB). If a capacitor is put from pin 1 to 8, bypassing the 1.35 kX 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 kX resistor). For 6 dB effective bass boost: R j 15 kX, the lowest
value for good stable operation is R e 10 kX if 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.
2
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
Voltage Gain vs Frequency
Distortion vs Frequency
Distortion vs Output Power
Device Dissipation vs Output
PowerÐ4X Load
Device Dissipation vs Output
PowerÐ8X Load
Device Dissipation vs Output
PowerÐ16X Load
TL/H/6976 – 5
3
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
4
Typical Applications (Continued)
AM Radio Power Amplifier
TL/H/6976 – 11
Note 1: Twist supply lead and supply ground very tightly.
Note 4: R1C1 band limits input signals.
Note 2: Twist speaker lead and ground very tightly.
Note 5: All components must be spaced very close to IC.
Note 3: Ferrite bead is Ferroxcube K5-001-001/3B with 3 turns of wire.
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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