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LM386 Low Voltage Audio Power Amplifier
September 1997
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.
Features
n n n n n n n n n 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
n n n n n n n n 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
Top View Order Number LM386M-1, LM386MM-1, LM386N-1, LM386N-3 or LM386N-4 See NS Package Number M08A, MUA08A or N08E
(c) 1999 National Semiconductor Corporation
DS006976
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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) 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
-65C to +150C 0C to +70C +150C
Dual-In-Line Package Soldering (10 sec) +260C Small Outline Package (SOIC and MSOP) Vapor Phase (60 sec) +215C Infrared (15 sec) +220C See AN-450 "Surface Mounting Methods and Their Effect on Product Reliability" for other methods of soldering surface mount devices. Thermal Resistance 37C/W JC (DIP) 107C/W JA (DIP) 35C/W JC (SO Package) 172C/W JA (SO Package) 210C/W JA (MSOP) 56C/W JC (MSOP)
Electrical Characteristics (Notes 1, 2)
TA = 25C Parameter Operating Supply Voltage (VS) LM386N-1, -3, LM386M-1, LM386MM-1 LM386N-4 Quiescent Current (IQ) Output Power (POUT) LM386N-1, LM386M-1, LM386MM-1 LM386N-3 LM386N-4 Voltage Gain (AV) Bandwidth (BW) Total Harmonic Distortion (THD) Power Supply Rejection Ratio (PSRR) 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 25C, the device must be derated based on a 150C maximum junction temperature and 1) a thermal resistance of 80C/W junction to ambient for the dual-in-line package and 2) a thermal resistance of 170C/W for the small outline package.
Conditions
Min 4 5
Typ
Max 12 18
Units V V mA mW mW mW dB dB kHz % dB k nA
VS = 6V, VIN = 0 VS = 6V, RL = 8, THD = 10% VS = 9V, RL = 8, THD = 10% VS = 16V, RL = 32, THD = 10% VS = 6V, f = 1 kHz 10 F from Pin 1 to 8 VS = 6V, Pins 1 and 8 Open VS = 6V, RL = 8, POUT = 125 mW f = 1 kHz, Pins 1 and 8 Open VS = 6V, f = 1 kHz, CBYPASS = 10 F Pins 1 and 8 Open, Referred to Output 250 500 700
4 325 700 1000 26 46 300 0.2 50 50 250
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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 k 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 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 k resistor). For 6 dB effective bass boost: R 15 k, the lowest value for good stable operation is R = 10 k if pin 8 is open. If pins 1 and 8 are bypassed then R as low as 2 k 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 with a 50 k 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 k 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, 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 k 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 F capacitor or a short to ground depending on the dc source resistance on the driven input.
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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 Load
Device Dissipation vs Output Power -- 8 Load
Device Dissipation vs Output Power -- 16 Load
DS006976-17
DS006976-18
DS006976-19
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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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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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Physical Dimensions
inches (millimeters) unless otherwise noted
SO Package (M) Order Number LM386M-1 NS Package Number M08A
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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
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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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