MH88610 Subscriber Line Interface Circuit (SLIC) Preliminary Information Features ISSUE 6 • Transformerless 2-wire to 4-wire conversion • Battery and ringing feed to line • Off-hook and dial pulse detection • Ring ground over-current protection • Loop length detection • Constant current feed April 1995 Ordering Information MH88610 20 Pin SIL Package 0°C to 70°C Description Applications The Mitel MH88610 Subscriber Line Interface Circuit 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, loop length and dial pulse detection. The device is fabricated using thick film hybrid technology in a 20-pin single in-line package. Line interface for: • PABX • Intercoms • Key Telephone Systems • Control Systems LPGND TF TIP RING RF VBat VDD VEE GNDA 2-Wire to 4-Wire Conversion Current &Voltage Sensing VR VX RV Over Current Protection Constant Current Feed VRef Loop Supervision LOOP SHK CAP Figure 1 - Functional Block Diagram 2-97 MH88610 Preliminary Information TF LPGND VR VRef VEE GNDA LOOP VX TIP RING RF VDD IC IC RV IC NC 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 # Name 1 TF 2 LPGND 3 VR Voice Receive (input) is the 4 wire analog signal to the SLIC. 4 VRef Voltage Reference (Input) to set the line current feed to the subscriber line. 5 VEE Negative Power Supply Voltage (-5V). 6 GNDA Analog Ground (0V). 7 LOOP Loop Monitor Voltage (Output). is proportional to the loop length. 8 VX Voice Transmit (Output) is the 4-wire analog signal from the SLIC. 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 VDD Positive Power Supply Voltage. 13 IC Internal Connection. Pin cut short. 14 IC Internal Connection. Pin cut short. 15 RV Ring Feed Voltage connects to pin 11 (RF) through a normally closed ring relay. 16 IC Internal Connection. Pin cut short. 17 NC No Connection. 18 VBat Negative Battery Feed Supply Voltage. 19 CAP Connects external capacitor and resistor to ground for ring trip filter control. 20 SHK Switch Hook Detect (Output). Digital output of an open-collector comparator. This output will go low (VEE) when the subscriber line resistance falls below a set threshold value indicating that the telephone set has gone off-hook. This output can be monitored for dial pulse collection. 2-98 Description TF Tip Feed. Internal connection. Normally connects a pair of external diodes for protection. Loop Ground. is the system ground reference with respect to VBat. MH88610 Preliminary Information Functional Description The MH88610 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 an from devices such as the voice codec or switching circuit. The SLIC also provides two status signals. switch hook (SHK) and loop length (Loop). The Loop signal is an analog voltage which is proportional to the loop length and the SHK goes low when the telephone set is off-hook. Constant Current Feed The MH88610 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. This gives the loop current as: ILoop = 25 - (VRef) mA (+2 mA) 1.25 Switch Hook Detection When the DC current exceeds an internal threshold level, the switch hook (SHK) will go low. 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 high impedance (open collector output) 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 (e.g., 90Vrms=+/-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. been detected an external circuit 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 GNDA to the Ring Trip Filter Control pin will switch in the filter, whilst removing GNDA, (with the switch in a tristate condition), will switch out the filter. For applications using DTMF signalling, the capacitor can be permanently connected to ground. 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. Components List R1 =Resistor 1/4w, + 5%, 30.0kΩ R2 =Resistor 1/4w, + 5%, 750kΩ R3 =Resistor 1/4w, + 5%, 3.9kΩ R4 =Resistor 1/4w, + 5%, 4.7kΩ R5 =Resistor 1/4w, + 5%, 43kΩ R6 =Resistor 1/4w, + 5%, 470kΩ RV1*, RV2* =Var. 160 VRMS, 250V,10J D1*, D3*, D4* =Diode Rect., 200V, 1A IN4003 D2 =Diode Rect., 200V, 1A IN4003 D5 =Diode Sw., 75V, 02A, 0.5W IN4148 Q =NPN, 2N2222 or equivalent K1 =Relay E/M, 12V, 1 form C C1*,C2*,C3*,C4*= Cap. Cer., 1.0µF, 50V, 20% C5 =Cap. Elec., 1.0µF, 16V 10% Note: Components marked * are optional for extra protection of the hybrid. A 1.0µF capacitor connected from pin 19 (CAP) to ground will provide adequate attenuation when ringing is applied. Once an off-hook condition has 2-99 MH88610 Preliminary Information -5V C4 9 VEE TIP TIP RV1 VRef 4 -11V C3 MH88610 LOOP RV2 7 10 RING RING D1 +12V 8 VBat VX 1 D5 TF VR K1 3 D2 Q1 VBat D3 D4 20 15 RV 2 R5 C5 CAP RF GNDA 18 VDD 12 6 C1 VBat -28V - + 19 R6 LPGND VBat ˜ -5V RING TRIP FILTER CONTROL C2 +5V ILOOP = VRef mA (+2mA) 0.423 Figure 3 - Application Circuit 2-100 R4 R3 R1 11 R2 SHK RINGING RELAY CONTROL MH88610 Preliminary Information Absolute Maximum Ratings* Parameter 1 Symbol Min VDD VEE VBat -15 -60 -40 DC Supply Voltage LPGND=GNDA 2 Storage Temperature TS 3 Package Power Dissipation PD Max Units +15 V V V 100 °C 2 W * Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied. Recommended Operating Conditions Parameter 1 Sym Operating Supply Voltage Min Typ† Operating Temperature Units VDD 4.75 5.0 5.25 VEE -5.25 -5.0 -4.75 VRef -23 -11 V -28 V VBat 2 Max 0 TO Comments V V 70 °C † Typical figures are at 25°C and are for design aid only. DC Electrical Characteristics† Characteristics 1 Sym Min Power Consumption IDD IEE 64 -3.4 PC 3 Constant Current Line Feed ILoop 24 4 Operating Loop Resistance RLoop 800 5 Off-Hook Threshold 6 Ring Ground Over-Current protection 7 Output High Voltage Loop (On-hook) VDD-2 8 Output High Source Current Loop (on-hook) 15 Output Low Voltage SHK Loop (off-hook) VEE 1.9 Output Low Sink Current SHK Loop (off-hook) 6 10 9 10 Typ‡ Max Units Test Conditions Supply Current VDD VEE 2 - Voltages are with respect to GNDA unless otherwise stated. 26 7.6 -5.0 mA mA 212 1110 mW mW 28 mA 1200 33 Ω VBat = -28V Ω VBat = -28V 42 mA VDD V mA VEE+1.5 2.4 16 20 Standby Active V V mA mA No Load RLOOP = 2.5V 10kΩ pull-up to 5V No Load V SHK = 1.5V VLoop = 2.5V † DC Electrical Characteristics are over recommended operating supply voltages. ‡ Typical figures are at 25°C with nominal +5V supplies and are for design aid only. 2-101 MH88610 Preliminary Information AC Electrical Characteristics Characteristics 1 Sym Ringing Voltage (rms) Min Typ* VR 17 Max Units 105 Vrms 25 Hz Test Conditions 2 Ring Frequency 3 Ringer Equivalence Number 4 Ring Trip Detect time 5 Input AC Impedance 2-wire 6 7 8 Gain 2-wire to Vx 0.60 0.62 0.70 dB Input 6dBm at 2-wire 9 Gain VR to 2-wire -6.75 -6.69 -6.65 dB Input 1.0V at VR 600Ω termination 10 2-wire Return Loss 20 dB Input 0.5 V 1kHz 600Ω 11 Transhybrid Loss 40 dB Input 0.5 V, 1kHz at V R 600Ω 12 Longitudinal Balance 45 dB Input 0.5V, 1kHz metallic output voltage 13 Total Harmonic Distortion at Vx % Input 6dBm at 2-wire REN 3 200 600 Ω Input Impedance at VR 230 kΩ Output Impedance at Vx 1 Ω Zin THL at THD at Tip and Ring 14 Common Mode Rejection Ratio 2-wire to Vx CMRR 15 Idle channel Noise (at Vx) Nc 16 Power supply rejection ratio VDD 0.1 1.0 0.1 1.0 40 15 % Input 1.0V at V R dB Input 0.5Vrms, 1KHz at metallic output voltage dBrnC C- Message PSRR 39 dB At VX, ripple at Vpp, 1kHz VDD 37 dB VEE 23 dB VBAT 23 dB At 2-Wire, ripple at 1Vpp, 1kHz At VX, ripple at 1Vpp, 1kHz At 2-Wire, ripple at 1Vpp, 1kHz * Typical figure are at 25°C and are for design aid only. 2-102 ms MH88610 Preliminary Information 0.080 Max (2.0 Max) Side View 2.00 + 0.020 (50.8 + 0.5) 0.52+0.02 (13.2+0.5) 1 2 3 4 19 20 0.010 + 0.002 (0.25 + 0.05) 0.12 Max (3.1 Max) 0.05 + 0.01 (1.3 + 0.5) Notes: 1) Not to scale 2) Dimensions in inches). 3) (Dimensions in millimetres). * Dimensions to centre of pin & tolerance non accumulative. * 0.05 + 0.02 (1.3 + 0.05) * 0.020 + 0.05 (0.51 + 0.13) * 0.18 + 0.02 (4.6 + 0.5) 0.100 + 0.10 (2.54 + 0.13) Figure 4 - Mechanical Data 2-103 MH88610 Notes: 2-104 Preliminary Information