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MH88612
Subscriber Line Interface Circuit (SLIC) Preliminary Information
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 drive output Power V Bat Denial Wide operating range
MH88612
ISSUE 4
April 1995
Ordering Information
20 Pin SIL Package
0C to 70C
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 film hybrid technology in a 20-pin single in-line package.
Applications
Line interface for: * * * * PABX Intercoms Key Telephone Systems Control Systems
LPGND
VBat
PD
VDD
VEE
AGND
Power Denial
TF TIP RING RF RV VRLY RC RD CD
Current & Voltage Sensing
2-Wire to 4-Wire Conversion
VR VX
Over Current Protection Relay Drive Circuit Constant Current Feed Loop Supervision
VRef CAP
SHK
FIgure 1 - Functional Block Diagram
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MH88612
Preliminary Information
TF LPGND VR VRef VEE AGND PD VX TIP RING RF VDD RC RD RV VRLY CD VBat CAP SHK
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Figure 2 - Pin Connections
Pin Description
Pin # 1 2 3 4 Name TF LPGND VR VRef Description Tip Feed. Connects to external diode for protection. Loop Ground. is the system ground reference with respect to VBat. Normally tied with AGND. Voice Receive (input) is the 4 wire analog signal to the SLIC. Voltage Reference (Input) to set the constant current feed to the subscriber line. Constant current feed can be adjusted by the input voltage on the VRef. This pin can also be grounded for normal 25 mA loop current. Negative Power Supply Voltage (-5V). Analog Ground (0V). Power Denial (Input). A logic high will isolate the battery voltage to Tip/Ring. Voice Transmit (Output) is the 4-wire analog signal from the SLIC. Connects to the "Tip" lead of the telephone line . Connects to the "Ring" lead of the telephone line Ring Feed (Input) is normally connected to Ring relay for negative battery feed voltage and ringing voltage input. Positive Power Supply Voltage (+5V). Relay Control (Input). Active high. Open collector sinks current when RC is at logic high. Ring Feed Voltage connects to pin 11 (RF) through a normally closed relay. Relay voltage Supply (+5V). Clamping Diode. Connects to GNDA. Negative Battery Feed Supply Voltage (-48V). Connects external capacitor to ground for ring trip. Switch Hook Detect (Output). Active high.
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
VEE AGND PD VX TIP RING RF VDD RC RD RV VRLY CD VBat CAP SHK
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Preliminary Information
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.
MH88612
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 will switch in the filter, whilst removing AGND, (with the switch in a tri-state condition), will switch out the filter. For applications using DTMF signalling, the capacitor can be permanently connected to ground.
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 (VRef) that determines the constant feed current. If VRef (pin 4) is externally grounded, the constant current is set at 25mA. For a constant current setting between 18mA and 30mA, VRef can be set between 8.75 Vdc and -6.35 Vdc. The relationship is defined by the equation: I LOOP = 25 - (VRef) mA (+2 mA) 1.25
Current Limit
The Tip or Ring may accidentally short to ground. In such a case, current will only flow 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.
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.
Power Denial
The power denial function is a feature of the MH88612 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 ILoop is negligible and power consumption is minimised. The power denial function is useful for disabling a loop which may have a ground fault.
Ringing And Ring Trip Detection
In Figure 3 a ringing signal (e.g.90 Vrms=+/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 filtered out to give a true off-hook condition at SHK. A 1.0F capacitor connected from pin 19 (CAP) to ground will provide adequate attenuation when
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MH88612
Applications
Component List R1 R2 C1 D1,D2 K1 Options RV1, RV2 D3, D4
Preliminary Information
= 1/4 W, + 10% 200 = 1/4W, + 5% 470 = Cap. Elec., 1.0F, + 10%, 25V = Diode Rect., 200V, 1A, IN4003 = Relay E/M, 5 or 6V, 1 Form C Decoupling capacitors (Cap. Cer 0.1F, 50% +20%) should be added to V DD, V EE, VBat, VRef and VRLY for extra protection of the hybrid. 160 Vrms, 250V 10J Diode Rect., 200V, 1A 1N4003.
R1
90Vrms SUPERIMPOSED ON -48VDC
K1 VBAT D4 D3
11
RF
MH88612
3
1 TF 15 2 RV LPGND
VR
D2
D1
VX
8
VBAT
9
TIP
4 VRef
RV1 SHK RV2 10 RING 13 RC +5V 16 VRLY K1 14 CAP RD 19 C1 PD 7 20
-
+
Ring Trip Filter Control
17 CD VBat 18
VDD 12
VEE 5
GNDA 6
R2
-48V
+5V
-5V
Figure 3 - Application Circuit
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Preliminary Information
Absolute Maximum Ratings*
Parameter 1 DC Supply Voltage LPGND = AGND Symbol VDD VEE VBat VRLY VRef TS PD Min 0.3 -15 -60 -0.3 -60 -40 Max +15 +0.3 +0.3 +40 +15 100 2
MH88612
Units V V V V V C W
2 3
Storage Temperature Package Power Dissipation
* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
Recommended Operating Conditions
Parameter 1 Operating Supply Voltage Sym VDD VEE VRef VBat VRLY 2 Operating Temperature TO 0 -27 Min 4.75 -4.75 Typa 5.0 -5.0 0 -48 5 70 -60 Max 5.25 -5.25 Units V V V V V C Adjustable Comments
a. Typical figures are at 25C with nominal + 5V supplies and are for design aid only: not guaranteed and not subject to production testing.
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MH88612
Characteristics 1 Supply Current VDD VEE VBat 2 Power Consumption IDD IEE IBat PC ILoop ILoop RLoop 23 5.8 -2.6 500 210 1410 25 27 Sym Min Typ Max
Preliminary Information
DC Electrical Characteristics - Voltages are with respect to GNDA unless otherwise stated.
Units Test Conditions
mA mA A mW mW mA
PD = Logic High Standby Active V Ref = AGND V Bat = -48V Adjustable with Ext. V Ref input, VBat = -48V V Bat = -48V @ ILoop = 18mA, R Loop includes telephone set
3
Constant Current Line Feed
4
Adjustable Loop Current Range
18
30
mA
5
Operating Loop Resistance
1200
6
Ring Ground Over-Current protection Off-Hook Detect Output Low Voltage (On-hook) Output High Voltage (Off-hook) Off- Hook Detect Output Low Current (on-hook) Output High Current. (off-hook) RC, PD Control Input Input Low Volt. (no activation) Input High Volt. (activation) RC, PD control Input Input Low Current (no activation) Input high current (activation)
40
mA
7
Active high logic VOL VOH IOL IOH VIL VIH IIL IIH 0.4 2.7 V V
8
8 -400
mA A Active high logic V V A mA
9
0.7 2.0
10
-50 50
DC Electrical Characteristics are over recommended operating supply voltages. Typical figures are at 25C with nominal +5V supplies and are for design aid only.
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Preliminary Information
AC Electrical Characteristics
Characteristics 1 2 3 4 5 6 7 Ringing Voltage (rms) Ringer Equivalence Number Ring Trip Detect time Input AC Impedance 2-wire Input Impedance at VR Output Impedance at Vx Gain 2-wire to Vx Gain relative to Gain @ 1kHz 8 Gain VR to 2-wire Gain relative to Gain @ 1kHz 9 2-wire Return Loss over 300-3400Hz Transhybrid Loss THL 20 Zin Sym VRING REN 200 600 100 10 -1.0 +0.1 -1.0 +0.15 30 dB dB dB Min 17 Typ* Max 90 25 3 ms k dB Units Vrms Hz
MH88612
Test Conditions Superimposed on VBAT = -48V
Input 3dBm, 1kHz across Tip and Ring, 300-3400 Hz (Input 1.0 Vrms 1kHz at VR ZLoad = 600 300 - 3400 Hz 600 Input 0.5 Vrms , 1kHz across Tip and Ring, ZLoad = 600 Input 0.5 Vrms, 1kHz at VR ZLoad= 600 Input 0.5 Vrms Input 3dBm, 1 kHz across Tip and Ring, Input 1.0 Vrms 1kHz at VR Input 0.5Vrms, 1kHz
10
20
30
dB
11 12
Longitudinal to Metallic Balance over 300-3400 Hz Total Harmonic Distortion at Vx at Tip and Ring THD
50
55 0.1 1.0
dB %
0.1 CMRR 40 50
1.0
% dB
13
Common Mode Rejection Ratio 2-wire to Vx Idle channel Noise (at Vx) Power supply rejection ratio VDD VEE VBat
14 15
Nc PSRR 26 26 26
12
dBrnC
C- Message
dB dB dB
1 VPP ripple, 1kHz on VDD/VEE/V BAT, measure at Vx and across Tip and Ring
* Typical figures are at 25C and are for design aid only.
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MH88612
Preliminary Information
Side View
0.080 Max (2.0 Max)
2.00 + 0.020 (50.8 + 0.5)
0.52+0.02 (13.2+0.5)
1234
19 20
0.010 + 0.002 (0.25 + 0.05) 0.12 Max (3.1 Max) 0.05 + 0.01 (1.3 + 0.5) * 0.05 + 0.02 (1.3 + 0.05) 0.020 + 0.05 (0.51 + 0.13) * *
Notes: 1) Not to scale 2) Dimensions in inches). 3) (Dimensions in millimetres). *Dimensions to centre of pin & tolerance non accumulative.
0.18 + 0.02 (4.6 + 0.5)
0.100 + 0.10 (2.54 + 0.13)
Figure 4 - Mechanical Data
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