low voltage audio power amplifier lm386n/d d e s c r i p t i o n outline drawing the lm 386 is a power amplifier designed for use in low voltage consum er 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 autom a tically biases to one-half the supply voltage. the quiescent power drain is only 24 dip8 m illiwatts when operating from a 6 volt supply , m a king the d386 ideal for battery operation. fea t ure battery operation m i n i mu m e x t e r n a l p a r t s wide supply voltage range: 4v?12v low quiescent current drain: 4m a voltage gains from 20 to 200 sop8 available in 8 pin dip package a p p l i c a t i o n pin configura tion a m - f m r a d i o a m p l i f i e r s portable tape player am plifiers intercom s tv sound sy stem s line drivers ultrasonic drivers sm all servo drivers power converters tiger electronic co.,ltd
lm386n/d equiv a lent schema tic and connection diagrams absolute maximum ra tings (t a=25 c) c h a r a c t e r i s t i c s y m b o l v a l u e u n i t maxim u m input v o ltage v in 0.4 v supply v o ltage vcc 15 v s o p 8 6 6 0 maxim u m power disspation dip8 p d 1200 mw soldering tem p erature(10 sec.) t s 2 6 0 c junction t e m p erature tj 150 c operating t e m p erature t a m b -10~+70 c s t orage t e m p erature t s tg -40~125 c electrical characteristics (unless otherwise specified: vcc=6v , r l =8 , f=1khz , t a m b =25 ) c h a r a c t e r i s t i c s t e s t c o n d i t i o n s sy m bol m i n t y p max u nit operating supply voltage v c c 1 2 v quiescent current vcc=6v v in =0 i c c - 4 8 m a vcc=6v , r l =8 ? thd=10% 2 5 0 3 2 5 output power vcc=9v , r l =8 ? thd=10% po 5 0 0 7 0 0 mw vcc=6v , f=1khz - 26 - voltage gain 10 ffrom pin 1 to 8 av - 4 6 - db bandwidth vcc=6v pins 1 and 8 open b w - 3 0 0 - k h z total harm onic distortion vcc=6v r l =8 ? po=125mw f=1khz pins 1 and 8 open t h d - 0 . 2 - % power supply rejection ratio vcc=6v f=1khz c byp a s s =1 0 pins 1 and 8 open referred to output p s r r 5 0 d b input resistance r in - 5 0 - k input bias current vcc=6v pins 2 and 3 open i b - 2 5 0 - n a
lm386n/d application hints gain control to make the lm 386 a more versatile amplifier, two pins (1and 8) are provided for gain control. with pins 1 and 8 open the 1.35 kw resistor sets the gain at 20 (26 db). if a capacitoris put from pin 1 to 8, bypassing the 1.35 kw 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 kw resistor). for 6 db effective bass boost: r . 15 kw, the lowest value for good stable operation is r = 10 kw if pin 8 is open. if pins 1 and 8 are by passed then r as low as 2 kw 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 bi ased to ground with a 50 kw 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 d386 is higher than 250 kw 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 kw, 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 elim inate 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 lm 386 with higher gains (bypassing the 1.35 kw 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.
lm386n/d applica t ion circuit 10k 0.05uf 250uf 10 - + 6 1 8 5 7 4 3 2 vi n vs lm 386 10 k 0.05u 250u 10 - + 6 1 8 5 7 4 3 2 vi n vs lm386 10u bypass fig1 am plifier with gain = 20 fig2 am plifier with gain = 200 ( m i n i m u m p a r t s ) 220 0. 05uf 250uf 10 - + 6 1 8 5 7 4 3 2 vs lm386 10uf ??a rl 390 0. 01uf 4. 7k vo 10k 0.05uf 250uf 10 - + 6 1 8 5 7 4 3 2 vin vs lm 386 10uf 1.2k fig3 am plifier with gain = 50 fig4 low distortion power wienbridge oscillator 50uf - + 6 1 8 5 7 4 3 2 vs lm386 rl 30k 0.1uf 1k vo 10k 10k 0.05uf 250uf 10 - + 6 1 8 5 7 4 3 2 vi n vs lm386 rl 10k 0.033uf vo fig5 am plifier with bass boost fig6 square wave oscillator
lm386n/d 10k 0.05uf 250uf 10k - + 6 1 8 5 7 4 3 2 vi n vs lm386 10uf 0.05uf 2200pf cc vol 10uf 47 ? 8 f i g 7 a m r a d i o p o w e r a m p l i f i e r typical performance characteristics
lm386n/d
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