LM386 Low Voltage Audio Power Amplifier

LM386 Low Voltage Audio Power Amplifier
LM386
Low Voltage Audio Power Amplifier
General Description
Features
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.
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Battery operation
Minimum external parts
Wide supply voltage range: 4V–12V or 5V–18V
Low quiescent current drain: 4 mA
Voltage gains from 20 to 200
Ground referenced input
Self-centering output quiescent voltage
Low distortion
Available in 8 pin MSOP package
Applications
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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
Small Outline,
Molded Mini Small Outline,
and Dual-In-Line Packages
DS006976-2
DS006976-1
© 1997 National Semiconductor Corporation
DS006976
Top View
Order Number LM386M-1,
LM386MM-1, LM386N-1, LM386N-3
or LM386N-4
See NS Package Number
M08A, MUA08A or N08E
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LM386 Low Voltage Audio Power Amplifier
September 1997
Absolute Maximum Ratings
(Note 2)
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
37˚C/W
θJC (DIP)
107˚C/W
θJA (DIP)
35˚C/W
θJC (SO Package)
172˚C/W
θJA (SO Package)
210˚C/W
θJA (MSOP)
56˚C/W
θJC (MSOP)
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 3)
(LM386N)
(LM386M)
(LM386MM-1)
Input Voltage
Storage Temperature
Operating Temperature
Junction Temperature
Soldering Information
15V
22V
1.25W
0.73W
0.595W
± 0.4V
−65˚C to +150˚C
0˚C to +70˚C
+150˚C
Electrical Characteristics(Notes 1, 2)
TA = 25˚C
Parameter
Conditions
Min
Typ
Max
Units
Operating Supply Voltage (VS)
LM386N-1, -3, LM386M-1, LM386MM-1
4
12
V
LM386N-4
5
18
V
8
mA
Quiescent Current (IQ)
VS = 6V, VIN = 0
4
Output Power (POUT)
LM386N-4
VS = 6V, RL = 8Ω, THD = 10%
VS = 9V, RL = 8Ω, THD = 10%
VS = 16V, RL = 32Ω, THD = 10%
Voltage Gain (AV)
VS = 6V, f = 1 kHz
26
10 µF from Pin 1 to 8
VS = 6V, Pins 1 and 8 Open
VS = 6V, RL = 8Ω, POUT = 125 mW
f = 1 kHz, Pins 1 and 8 Open
46
dB
300
kHz
0.2
%
50
dB
50
kΩ
250
nA
LM386N-1, LM386M-1, LM386MM-1
LM386N-3
Bandwidth (BW)
Total Harmonic Distortion (THD)
Power Supply Rejection Ratio (PSRR)
VS = 6V, f = 1 kHz, CBYPASS = 10 µF
250
325
mW
500
700
mW
700
1000
mW
dB
Pins 1 and 8 Open, Referred to Output
Input Resistance (RIN)
Input Bias Current (IBIAS)
VS = 6V, Pins 2 and 3 Open
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 functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee 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 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.
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Application Hints
INPUT BIASING
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.
The schematic shows that both inputs are biased to ground
with a 50 kΩ 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 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.
3
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Typical Performance Characteristics
Quiescent Supply Current
vs Supply Voltage
Power Supply Rejection Ratio
(Referred to the Output)
vs Frequency
DS006976-5
Peak-to-Peak Output Voltage
Swing vs Supply Voltage
DS006976-13
DS006976-12
Voltage Gain vs Frequency
Distortion vs Frequency
DS006976-15
DS006976-14
Device Dissipation vs Output
Power — 4Ω Load
Device Dissipation vs Output
Power — 8Ω Load
DS006976-17
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Distortion vs Output Power
DS006976-18
4
DS006976-16
Device Dissipation vs Output
Power — 16Ω Load
DS006976-19
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
5
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Typical Applications
(Continued)
Frequency Response with Bass Boost
DS006976-10
AM Radio Power Amplifier
DS006976-11
Note 4: Twist Supply lead and supply ground very tightly.
Note 5: Twist speaker lead and ground very tightly.
Note 6: Ferrite bead in Ferroxcube K5-001-001/3B with 3 turns of wire.
Note 7: R1C1 band limits input signals.
Note 8: All components must be spaced very closely to IC.
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7
Physical Dimensions
inches (millimeters) unless otherwise noted
SO Package (M)
Order Number LM386M-1
NS Package Number M08A
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8
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
8-Lead (0.118” Wide) Molded Mini Small Outline Package
Order Number LM386MM-1
NS Package Number MUA08A
9
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LM386 Low Voltage Audio Power Amplifier
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Dual-In-Line Package (N)
Order Number LM386N-1, LM386N-3 or LM386N-4
NS Package Number N08E
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sonably expected to cause the failure of the life support
the body, or (b) support or sustain life, and whose faildevice or system, or to affect its safety or effectiveness.
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with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
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