l3845 trunk interface on chip polarity guard meets dc line characteristics of either ccitt and eia rs 464 specs pulse function high ac impedance off hook-status detection output low external component count description the circuit provides dc loop termination for ana- log trunk lines. the v-i characteristics is equivalent to a fixed voltage drop (zener like characteristic) in series with an external resistance that determines the slope of the dc characteristic. an external low voltage electrolytic capacitor causes the circuit to exhibit a very high imped- ance to all ac signal above a minimum frequency that is determined by the capacitor itself and by a 20 k nominal resistor integrated on the chip. the off-hook status is detected all the time a typic of 8 ma is flowing into the circuit. in this con- dition a constant current generator is activated to supply an external device (typically an optocou- pler) without affecting the ac characteristic of the circuit. when pulse dialing is required the pulse input (pin 3) connected to v- causes the device to re- duce the fixed dc voltage drop and to exhibit a pure resistive impedance equal to the external re- sistor. this is advanced information on a new product now in development or undergoing evaluation. details are subject to change withou t notice. september 2003 ? polarity guard dc line termination of hook detection circuit 1 7 8 3 4 in1 in2 562 act dct v- r2 r3 r1 s1 c1 s2 v+ pulse hd0 d96tl263 block diagram minidip so8 so20w (12+4+4) ordering numbers: l3845b l3845d l3845-20 1/8
absolute maximum ratings symbol parameter value unit v l max line voltage (pulse duration 10 ms max) 20 v i l max line current 150 ma p tot total power dissipation at tamb = 70 c800mw t op operating temperature C 40 to + 70 c t srg , t j storage and junction temperature C 55 to + 150 c thermal data symbol parameter minidip so8 so20 unit r th j-amb thermal resistance junction-ambient (*) max. 80 140 to 180 50 to 70 c/w (*) mounted on fr4 boards pin connection (top view) pulse hd0 nc subs subs subs subs nc act v+ nc subs subs subs subs nc in1 v- 1 3 2 4 5 6 7 8 9 18 17 16 15 14 12 13 11 19 10 20 dct in2 so20 so20 in1 v- pulse hd0 1 3 2 4 act dct in2 v+ 8 7 6 5 dip8 minidip and so8 subs = the pin is electrically and thermally in good contact with the chip sustrate. connect to pcb copper tracks, for heat dis sipation the tracks shall preferably be electrically connected to pin 20 (internally bonded to the chip substrate) or left flo ating. a higher track density and/or area assures a r th j-amb towards the lower limit. l3845 2/8
dc electrical characteristics (i l = 10 ma to 100 ma, r 1 = 56 w , s 1 = open, t amb = + 25 c, unless otherwise specified) symbol parameter test condition min. typ. max. unit v l line voltage (normal mode) pulse = open il = 10 ma i l = 20 ma i l = 100 ma 5 6 12 v v v v lp line voltage (pulse mode) pulse = v C i l = 20 ma i l = 35 ma i l = 80 ma 4 5.5 9.5 v v v i hn on/off-hook line current detection threshold 6.5 9.5 ma i hf off/on-hook line current detection threshold 59.2ma i out off-hook output drive current at pin hdo il = 10 ma i l 3 20 ma 1.5 1.8 ma ma v pm pulse input low voltage 0.8 v i pm pull-up input current at pin pulse (pulse mode) il = 100 ma pulse = v C 20 m a i nm imput current at pin pulse (normal mode) 3 m a ac electrical characteristics (i l = 10ma to 100ma, r 1 = 56 w , r 2 = 470k w , r 3 = 130 k w , t amb = + 25 c, unless otherwise specified) symbol parameter test condition min. typ. max. unit z l ac line impedance s 1 = open, s 2 = open c 1 = 2.2mf f = 1khz 20 k w sending/receiving distortion s 1 = open, s 2 = open f = 1khz v ac-l = 775mvrms i l = 15 to 100ma 2% sending/receiving distortion s 1 = closed; s 2 = open v ac-l = 1.3vrms 2 % sending/receiving distortion s 1 = open; s 2 = closed v ac-l = 1.9vrms 2(*) % (*) not tested, guaranteed only by design. application information with the use of this circuit it is possible to termi- nate an analog trunk so that all the dc current component is flowing in the trunk termina- tion circuit while the ac component is de- coupled with a low voltage capacitor and can be used with a small and low cost audio coupler transformer to provide the ac balancing termina- tion and two to four wire conversion. therefore it is usefull both for modem and pabx systems. figure 1 gives the typical application circuit ; it is worth to note that the trunk termination circuit, together with the ls5018 transient sup- pressor provides a compact and low cost module fully protected against lightning or overvoltages frequently present on telephone lines. the pulse input when connected to v- allows the device to reduce the line voltage and to show a resistive impedance equal to r1 to the line. when pulse input is left open, this function is disable. l3845 3/8
figure 1: typical application. l3845 4/8
outline and mechanical data dim. mm inch min. typ. max. min. typ. max. a 3.32 0.131 a1 0.51 0.020 b 1.15 1.65 0.045 0.065 b 0.356 0.55 0.014 0.022 b1 0.204 0.304 0.008 0.012 d 10.92 0.430 e 7.95 9.75 0.313 0.384 e2.54 0.100 e3 7.62 0.300 e4 7.62 0.300 f 6.6 0.260 i 5.08 0.200 l 3.18 3.81 0.125 0.150 z 1.52 0.060 minidip l3845 5/8
dim. mm inch min. typ. max. min. typ. max. a 1.75 0.069 a1 0.1 0.25 0.004 0.010 a2 1.65 0.065 a3 0.65 0.85 0.026 0.033 b 0.35 0.48 0.014 0.019 b1 0.19 0.25 0.007 0.010 c 0.25 0.5 0.010 0.020 c1 45 (typ.) d (1) 4.8 5.0 0.189 0.197 e 5.8 6.2 0.228 0.244 e 1.27 0.050 e3 3.81 0.150 f (1) 3.8 4.0 0.15 0.157 l 0.4 1.27 0.016 0.050 m 0.6 0.024 s8 (max.) (1) d and f do not include mold flash or protrusions. mold flash or potrusions shall not exceed 0.15mm (.006inch). so8 outline and mechanical data l3845 6/8
11 0 11 20 a e b d e l k h a1 c so20mec h x 45? so20 dim. mm inch min. typ. max. min. typ. max. a 2.35 2.65 0.093 0.104 a1 0.1 0.3 0.004 0.012 b 0.33 0.51 0.013 0.020 c 0.23 0.32 0.009 0.013 d 12.6 13 0.496 0.512 e 7.4 7.6 0.291 0.299 e 1.27 0.050 h 10 10.65 0.394 0.419 h 0.25 0.75 0.010 0.030 l 0.4 1.27 0.016 0.050 k 0? (min.)8? (max.) outline and mechanical data l3845 7/8
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