. low current consumption, in order to allow the parallel operation of 4 devices . integrated rectifier bridge with zener diodes to protect against overvoltages . little external circuitry . tone and switching frequencies ad- justable by external components . integrated voltage and current hysteresis description LS1240A is a monolithic integrated circuit designed to replace the mechanical bell in telephone sets in connection with an electro-acoustical converter. it can drive directly a piezoceramic converter (buzz- er)or a dynamic loudspeaker. the output current capability of LS1240A is higher than standard ringer. for driving a dynamic loud- speaker LS1240A can simply use a decoupling ca- pacitor, thus eliminating the usual transformer. no current limitation is provided on the output stage of LS1240A, so a minimum load dc of 50 w is ad- viced, in series with a proper capacitor. the two tone frequencies generated are switched by an internal oscillator in a fast sequence and made audible across an output amplifier in the loud- speaker, both tone frequencies and the switching frequency can be externally adjusted. the supply voltage is obtained from the ac ring sig- nal and the circuit is designed so that noise on the line or variations of the ringing signal cannot affect correct operation of the device. so8 minidip ordering numbers minidip so8 LS1240A LS1240Ad1 pin connection (top view) wing shing computer components co., (h.k.)ltd. tel:(852)2341 9276 fax:(852)2797 8153 homepage: http://www.wingshing.com e-mail: wsccltd@hkstar.com
figure 1 : test circuit. r1 = 2.72 10 4 f1 ( hz ) ( 1 - 0.04 ln f1 1943 ) f2 = 0.725 f1 f sweep = 750 c1 ( nf ) block diagram LS1240A
absolute maximum ratings symbol parameter value unit v ab calling voltage (f = 50 hz) continuous 120 v rms v ab calling voltage (f = 50 hz) 5s on/10s off 200 v rms dc supply current 30 ma t o p ope r ating temper a tur e C 0 t o + 7 0 c t stg storage and junction temperature C 65 to + 150 c thermal data symbol parameter value unit r t h j - a m b therma l resistance ju n c t ion-ambie n t ma x 0 0 c / w electrical characteristics (t amb = 25 c; v s = applied between pins 7-2 unless otherwise specified) symbol parameter test conditions min. typ. max. unit v s supply voltage 26 v i b current consumption without load (pins 8-1) v 8-1 = 9.3 to 25 v 1 .5 1.8 ma v o n activ a tion vo l tag e v o f f susta i n ing v o ltag e r d differential resistance in off condition (pins 8-1) 6.4 k w v out output voltage swing v s C 5 v i out short circuit current (pins 5-2) v s = 20v r l = 250 w 70 ma ac operation f 1 f 2 output frequencies f out1 f out2 v s = 26v, r 1 = 14k w v s = 0 v v s = 6v khz f out1 f out2 1.33 1.43 programming resistor range 8 56 k w f sweep sweep frequency r 1 = 14k w , c 1 = 100nf 5.25 7.5 9 .75 hz LS1240A
figure 2 : typical application with buzzer figure 3 : typical application with loudspeaker (no transformer needed) c 1 such that ? z load ? > 1 kw LS1240A
|
