1 features ? transformerless 2-wire to 4-wire conversion ? battery and ringing feed to line ? off-hook and dial pulse detection. ? ring ground over-current protection ? adjustable constant current feed. ? relay driver ? power denial ? wide operating range applications line interface for: ? pabx ? intercoms ? key telephone systems ? control systems description the slic provides a complete interface between a switching system and a subscriber loop. functions provided include battery feed and ringing feed to the subscriber line, 2-wire to 4-wire hybrid interfacing, constant current feed and dial pulse detection. the device is fabricated using thick ?lm hybrid technology in a 20-pin single in-line package. issue 2 february 1998 ordering information MH88612Bv-2 20 pin sil package 0 c to 70 c MH88612B subscriber line interface circuit (slic) advance information figure 1 - block diagram current and voltage sensing relay drive circuit constant current feed over current protection 2-wire to 4-wire conversion loop supervision power management tf tip ring rf rv vrly rc rd cd lpgnd vbat pd vcc vee agnd vr vx cap shk vref
MH88612B advance information 2 figure 2 - pin connections pin description pin # name description 1tf tip feed. connects to external diode for protection 2 lpgnd loop ground . is the system ground reference with respect to v bat. normally connected to agnd. 3vr voice receive (input) is the 4 wire analog signal to the device. 4 vref voltage reference (input) constant current feed can be adjusted by the input voltage on v ref . this pin can also be grounded for normal 25ma loop current. 5 vee negative power supply voltage (-5v). 6 agnd analog ground (0v). 7pd power denial (input) . a logic high will isolate the battery voltage to tip/ring. 8vx voice transmit (output) is the 4-wire analog signal from the device. 9 tip connects to the tip lead of the telephone line. 10 ring connects to the ring lead of the telephone line. 11 rf ring feed (input) is normally connected to ring relay for negative battery feed voltage and ringing voltage input. 12 vcc positive power supply voltage (+5v). 13 rc relay control (input) . active high. 14 rd open collector sinks current when rc is at logic high. 15 rv ring feed voltage connects to pin 11 (rf) through a normally closed relay. 16 vrly relay voltage supply (+5v). 17 cd clamping diode . connects to agnd 18 vbat negative battery feed supply voltage (-48v). 19 cap connects external capacitor to ground for ring trip. 20 shk switch hook detect (output). active high. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 tf lpgnd vr vref vee agnd pd vx tip ring rf vcc rc rd rv vrly cd vbat cap shk
advance information MH88612B 3 functional description the slic performs a transformerless 2-wire to 4- wire conversion of the analog signal. the 2-wire circuit is the balanced line going to the subscriber loop, while the 4-wire circuit is the audio signal going to and from devices such as the voice codec or switching circuit. the slic also provides a switch hook (shk) status output which goes high when the telephone is set off-hook. constant current feed the slic employs a complex feedback circuit to supply a constant feed current to the line. this is done by sensing the sum of the voltages across the internal feed resistors and comparing it to an input reference voltage (v ref ) that determines the constant feed current. if v ref (pin 4) is externally grounded, the constant current is set at 25ma. for a constant current setting between 18ma and 30ma, v ref can be set between 8.75 vdc and -6.35 vdc. the relationship is de?ned by the equation: iloop = v bat - v ref ma ( + 2 ma) 1.89 1.25 switch hook detection when the dc current exceeds an internal threshold level, the switch hook (shk) will go high. if the loop resistance is so high that v bat can no longer supply the required amount of loop current as determined by constant current supply circuit, the output of the switch hook (shk) will go low to indicate that the loop resistance is too high and the line is on hook. ringing and ring trip detection in figure 3 a ringing signal (eg. 90 vrms and -48vdc) is applied to the line by disconnecting pin 15 (rv) from pin 11(rf), and connecting the ringing voltage at pin 11 (rf) by use of the relay k1. the slic can detect an off-hook condition during ringing but there is a large ac component which must be ?ltered out to give a true off-hook condition at shk. a 1.0 m f capacitor connected from pin 19 (cap) to ground will provide adequate attenuation when ringing is applied. once an off-hook condition has been detected a logic low should be applied to pin 13 (rc) which will deactivate the relay (k1) to disconnect the ringing voltage from pin 11 and reconnect to pin 15. at that time the slic will revert to constant current feed operation. for applications requiring dial pulse detection the capacitor connection to ground should be controlled such that the capacitor is only connected during ringing. during off-hook conditions (closed loop), the capacitor should be switched out. this can be performed using a transistor, relay or system drive output of a codec. applying agnd to the ring trip filter control pin as shown in figure 4 will switch in the ?lter, whilst removing agnd, (with the switch in a tri-state condition), will switch out the ?lter. for applications using dtmf signalling, the capacitor can be permanently connected to ground. current limit the tip or ring of the telephone line may accidentally be shorted to ground. in such a case, current will only ?ow through the feed resistor. this high current will be sensed and reduced by the current limit circuit to a lower value to protect the internal circuitry. power denial the power denial function is a feature of the MH88612B which allows for powering down of the subscriber loop. a logic high voltage applied to the power denial input effectively removes the battery voltage from the loop driver circuitry. the resulting i loop is negligible and power consumption is minimized. the power denial function is useful for disabling a loop which may have a ground fault.
MH88612B advance information 4 figure 3 - application circuit vr vx shk pd cap agnd vee vcc vbat cd rd rc vrly ring tip tf lpgnd rv rf vbat 3 8 20 7 19 c1 6 5 12 18 -5v +5v -48v 17 14 16 13 10 9 1 2 15 11 d3 d1 d2 d4 tip ring +5v k1 r1 + - MH88612B k1 r2 ~ 90 vrms - + 48v protection circuit c2 c3 q1 r3 rc (pin 13) r4 components list r1 200 w 10%, 1/4w r2 470k w 5%, 1/4w r3, r4 10k w 5%, 1/4w c1 1.0 m f, 10%, 25v electrolytic capacitor c2, c3 0.1 m f 20%, 50v ceramic de-coupling capacitors d1, d2, d3, d4 diode recti?er 200v, 1a, in4003 q1 general purpose switching transistor k1 relay e/m, 5v or 6v 1form c protection circuit - depending on the application the protection circuit may need to provide over- voltage and/or over-current protection. in certain circumstances no protection will be required.
advance information MH88612B 5 * exceeding these values may cause permanent damage. functional operation under these conditions is not implied. ? typical ?gures are at 25?c with nominal supply voltages and are for design aid only absolute maximum ratings* parameter symbol min max units 1 dc supply voltage lpgnd = agnd v cc v ee v bat v rly v ref -0.3 -15 -80 -0.3 -60 +15 +0.3 +0.3 +40 +15 v v v v v 2 storage temperature t s -40 100 c 3 package power dissipation pd 2 w recommended operating conditions characteristics sym min typ ? max units test conditions 1 operating supply voltage v cc v ee v ref v bat v rly 4.75 -5.25 -60 5.0 -5.0 0 -48 5 5.25 -4.75 -27 v v v v v adjustable 2 storage temperature t s -40 100 c 2 storage temperature 3 t o 070 c dc electrical characteristics ? - voltages are with respect to gnda unless otherwise stated. characteristics sym min typ ? max units test conditions 1 supply current v cc v ee v bat i cc i ee i bat 6.6 -3.8 150 2 500 ma ma m a ma pd = logic high pd = logic low, idle 2 power consumption p c 160 1600 mw mw standby v bat = -48v active (off hook) 3 constant current line feed i loop 23 25 27 ma v ref = agnd, v bat = -48v 4 adjustable loop current range i loop 18 30 ma adjustable with ext. v ref input, v bat = -48v 5 operating loop resistance r loop 1200 w v bat = -48v @ i loop = 18ma, r loop includes telephone set 6 ring ground over-current protection 40 50 ma ma i loop = 25ma v bat = 48v i loop = 30ma v bat = 48v 7 off-hook detect output low voltage (on-hook) output high voltage (off-hook) v ol v oh 2.7 0.4 v v active high logic 8 off-hook detect output low current (on-hook) output high current. (off- hook) i ol i oh 8 -200 ma m a
MH88612B advance information 6 ? dc electrical characteristics are over recommended operating supply voltages. ? typical ?gures are at 25?c with nominal 5v supplies and are for design aid only. ? typical ?gures are at 25?c with nominal 5v supplies and are for design aid only. 9 rc, pd control input input low volt (no activation) input high volt (activation) v il v ih 2.0 0.7 v v active high logic lsttl compatible 10 rc, pd control input input low current (no activation) input high current (activation) i il i ih 50 0.5 m a ma 11 pd control input input low current input high current i il i ih 0.5 0.3 ma ma ac electrical characteristics characteristics sym min typ ? max units test conditions 1 ringing voltage (rms) v ring 17 90 25 v rms hz superimposed on v bat = -48v 2 ringer equivalence number ren 3 3 ring trip detect time 200 ms cap = 1uf 4 input ac impedance 2-wire zin 600 w 5 input impedance at v r 100 k w 6 output impedance at vx 10 w 7 gain 2-wire to vx gain relative to gain @ 1khz -1.3 -0.15 -1.0 -0.7 +0.15 db input 3dbm, 1khz across tip and ring 300-3400 hz 8 gain vr to 2-wire gain relative to gain @ 1khz -1.3 -0.15 -1.0 -0.7 +0.15 db db input 1.0 vrms 1khz at v r z load = 600 w 300 - 3400 hz 9 2-wire return loss over 300-3400hz rl 20 30 db input 0.5 vrms , 1khz across tip and ring, z load = 600 w 10 transhybrid loss thl 20 30 db input 0.5 vrms , 1khz at v r z load = 600 w 11 longitudinal to metallic balance over 300-3400 hz 50 55 db input 0.5 vrms 12 total harmonic distortion at vx at tip and ring thd 0.1 0.1 1.0 1.0 % % input 3dbm, 1 khz across tip and ring, input 1.0 vrms 1khz at v r 13 common mode rejection ratio 2-wire to vx cmrr 40 50 db input 0.5vrms, 1khz 14 idle channel noise nc 14 dbrnc c @ & vx message 15 power supply rejection ratio v cc v ee v bat psrr 26 26 26 db db db 1 v pp ripple, 1khz on vcc/v ee /v bat ,measure at vx and across tip & ring dc electrical characteristics ? - voltages are with respect to gnda unless otherwise stated. characteristics sym min typ ? max units test conditions
advance information MH88612B 7 figure 4 - mechanical data 1 0.6 max (15.24 max) 0.020 + 0.005 (0.5 + 0.13) 0.100 + 0.010 (1.25 + 0.51) 0.05 + 0.02 0.180 + 0.020 (4.57 + 0.51) (2.54 + 0.25) * * 0.12 max (3.05 max) 0.010 + 0.002 (0.25 + 0.05) 0.08 max (2.03 max) 2.120 max (53.85 max) notes: 1) not to scale 2) dimensions in inches. (dimensions in millimetres) * dimensions to centre of pin. 3) pin tolerances are non-accumulative. 4) recommended soldering conditions: wave soldering max. temp: 260?c for 10 secs.
MH88612B advance information 8 notes:
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