- a b in r c out v e b gnd a out a in v mic 1 2 4 3 r mic 8 7 5 6 - b - c 10 9 b out c in r e LC508 data sheet block diagram class a amplifier with 3 independent gain blocks features ? 1 m v input referred noise ? 1.0 to 5 vdc operating range ? 73 db typical gain (adjustable) ? 0.28 to 2.0 ma range of transducer current ? 1% electrical distortion ? the first and second blocks, or second and third blocks can be dc coupled ? 100 hz to 50 khz frequency response ? suitable for active filtering standard packaging ? 10 pin micropac ?10 pin plid ? ? 10 pin slt ? chip (52 x 49 mils) description the LC508 is a 10 pin class a amplifier utilizing gennum's proprietary low voltage bipolar jfet technology. it consists of 3 single ended, low noise inverting gain blocks. the first two blocks have a typical open loop gain of 50 db. the closed loop gain is set by the ratio of the feedback resistor to the source impedance. the third block is an open collector output stage with the bias being set by r e and v re at pin 8 which is 54 mv. typically, the gain of the first two blocks is set to 25 db each, with the third block at 23 db, giving a total gain of 73 db. gain trim can be accomplished with the use of a feedback resistor on the first block, while the volume control is used as the feedback control on the second block. this gives a volume control range greater than 40 db. document no. 500 - 61 - 12 revision date: january 2001 gennum corporation p.o. box 489, stn. a, burlington, ontario, canada l7r 3y3 tel. +1 (905) 632-2996 web site: www.gennum.com e-mail: hipinfo@gennum.com
2 500 - 61 - 12 fig. 1 test circuit parameter symbol conditions min typ max units gain (closed loop) a cl v out = 500 v rms 69 73 77 db amplifier current i amp i amp = i a + i mic 160 245 340 m a transducer current i trans h r e = 47.5 1.1 1.3 1.7 ma transducer current i trans l r e = 200 275 350 m a distortion thd v out = 500 v rms -1 4 % input referred noise irn nfb 0.2 to 10khz at 12db/oct - 1 2 m v stable with battery resistance to r b - - 22 w input bias current i b -50 0 50 na on chip emitter resistor r e - 200 - w emitter bias voltage (pin 8) v re -54 -mv microphone decoupling resistor r mic -4 -k w electrical characteristics conditions: supply voltage =1.3 vdc, frequency = 1 khz, temperature = 25 o c v mic pin connection
3 500 - 61 - 12 r vc r 1 all resistors in ohms, all capacitors in m f unless otherwise stated gain of stage a = 20 log 10 ( ) gain of stage b = 20 log 10 ( ) gain of stage c = 20 log 10 ( ) fig. 3 typical hearing aid application fig. 2 functional schematic ? r gt r s r l r e //47 v b =1.3 vdc 47 5 7 8 2 - b - a r e 50k 6 r l = 1k 4 3 1 r gt 3.9k 0.033 - c 0.015 10 9 50k r s 10 0.22 r vc 2.7k c s r mic r1 10 9 4 1 3 8 2 33k 5 7 r e 6 r mic all external resistors in ohms, all capacitors in m f unless otherwise stated
4 500 - 61 - 12 relative output (db) fig. 5 frequency response at various c s values 20 200 2k 20k frequency (hz) c s = 0.22 m f c s = 0.1 m f c s = 0.047 m f c s = 0.033 m f output (dbv) r vc = 47k r vc = 100k r vc = 22k r vc = 10k r vc = 3.3k 10 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -140 -120 -100 -80 -60 -40 -20 input (dbv) 10 5 0 -5 -10 -15 -20 -25 -30 -35 -40 60 55 50 45 40 35 30 25 20 4 2 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 fig. 4 i /o characteristics at various r vc values relative gain (db) fig.6 gain vs supply voltage 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 supply voltage (vdc) 10 100 1k 10k 100k frequency (hz) fig.7 preamplifier a open loop frequency response gain (db) -20 -10 0 10 20 30 40 50 temperature ( o c) -20 -10 0 10 20 30 40 50 temperature ( o c) relative transducer current ( m a) relative amplifier current ( m a) 60 50 40 30 20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 fig. 8 amplifier current vs temperature fig. 9 transducer current vs temperature 60 50 40 30 20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 document identification: data sheet the product is in production. gennum reserves the right to make changes at any time to improve reliability, function or design, in order to provide the best product possible. gennum corporation assumes no responsibility for the use of any circuits described herein and makes no representations that the y are free from patent infringement. ? copyright march 1983 gennum corporation. all rights reserved. printed in canada. revision notes: changes to standard packaging information gennum corporation mailing address: p.o. box 489, stn. a, burlington, ontario, canada l7r 3y3 tel. +1 (905) 632-2996 fax +1 (905) 632-2814 shipping address: 970 fraser drive, burlington, ontario, canada l7l 5p5 gennum japan corporation c-101, miyamae village, 2-10-42 miyamae, suginami-ku, tokyo 168-0081, japan tel. +81 (3) 3334-7700 fax: +81 (3) 3247-8839
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