MH88612 Subscriber Line Interface Circuit (SLIC) Preliminary Information Features ISSUE 4 • 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 April 1995 Ordering Information MH88612 20 Pin SIL Package 0°C to 70°C 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 PD VBat VDD VEE AGND Power Denial TF TIP RING RF Current & Voltage Sensing RV VRLY RC RD CD 2-Wire to 4-Wire Conversion VR Loop Supervision VRef Over Current Protection Relay Drive Circuit Constant Current Feed VX CAP SHK FIgure 1 - Functional Block Diagram 2-105 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 # Name 1 TF 2 LPGND 3 VR 4 VRef 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. 5 VEE Negative Power Supply Voltage (-5V). 6 AGND 7 PD Power Denial (Input). A logic high will isolate the battery voltage to Tip/Ring. 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 12 VDD 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 17 CD 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. 2-106 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. Analog Ground (0V). Ring Feed (Input) is normally connected to Ring relay for negative battery feed voltage and ringing voltage input. Positive Power Supply Voltage (+5V). Relay voltage Supply (+5V). Clamping Diode. Connects to GNDA. MH88612 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. 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 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 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. 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. 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. 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 1.0µF capacitor connected from pin 19 (CAP) to ground will provide adequate attenuation when 2-107 MH88612 Preliminary Information Applications Component List R1 R2 C1 D1,D2 K1 Options RV1, RV2 D3, D4 = 1/4 W, + 10% 200Ω = 1/4W, + 5% 470Ω = Cap. Elec., 1.0µF, + 10%, 25V = Diode Rect., 200V, 1A, IN4003 = Relay E/M, 5 or 6V, 1 Form C Decoupling capacitors (Cap. Cer 0.1µF, 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 K1 11 90Vrms VBAT SUPERIMPOSED ON -48VDC D4 D2 D3 D1 MH88612 1 TF 15 2 VBAT RF 9 VR 3 RV LPGND VX 8 4 TIP VRef RV1 SHK 20 RV2 10 RING PD 13 7 RC 16 +5V VRLY K1 14 19 C1 CAP RD 17 CD VBat 18 -48V VDD VEE 12 5 +5V GNDA -5V Figure 3 - Application Circuit 2-108 6 - Ring Trip Filter Control + R2 MH88612 Preliminary Information Absolute Maximum Ratings* Parameter Symbol Min Max Units VDD VEE VBat VRLY VRef 0.3 -15 -60 -0.3 -60 +15 +0.3 +0.3 +40 +15 V V V V V -40 100 °C 2 W 1 DC Supply Voltage LPGND = AGND 2 Storage Temperature TS 3 Package Power Dissipation PD * Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied. Recommended Operating Conditions Parameter 1 Operating Supply Voltage Sym Min Typa Max Units VDD 4.75 5.0 5.25 V VEE -4.75 -5.0 -5.25 V 0 VRef VBat -27 Operating Temperature TO -60 5 VRLY 2 -48 V 0 Comments Adjustable V V 70 °C a. Typical figures are at 25°C with nominal + 5V supplies and are for design aid only: not guaranteed and not subject to production testing. 2-109 MH88612 Preliminary Information DC Electrical Characteristics† - Voltages are with respect to GNDA unless otherwise stated. Characteristics 1 Sym Min Typ‡ Max Units 500 mA mA µA PD = Logic High mW mW Standby Active 27 mA V Ref = AGND V Bat = -48V 30 mA Adjustable with Ext. V Ref input, VBat = -48V 1200 Ω 40 mA 0.4 V V Supply Current VDD VEE VBat IDD IEE IBat 5.8 -2.6 PC 210 1410 2 Power Consumption 3 Constant Current Line Feed ILoop 23 4 Adjustable Loop Current Range ILoop 18 5 Operating Loop Resistance RLoop 6 Ring Ground Over-Current protection 7 Off-Hook Detect Output Low Voltage (On-hook) Output High Voltage (Off-hook) VOL VOH Off- Hook Detect Output Low Current (on-hook) Output High Current. (off-hook) IOL IOH 8 -400 mA µA RC, PD Control Input Input Low Volt. (no activation) Input High Volt. (activation) VIL VIH 0.7 V V IIL -50 µA IIH 50 mA 8 9 10 RC, PD control Input Input Low Current (no activation) Input high current (activation) 25 V Bat = -48V @ ILoop = 18mA, R Loop includes telephone set Active high logic 2.7 Active high logic 2.0 † 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. 2-110 Test Conditions MH88612 Preliminary Information AC Electrical Characteristics Characteristics Sym Min 17 1 Ringing Voltage (rms) VRING 2 Ringer Equivalence Number REN 3 Ring Trip Detect time 4 Input AC Impedance 2-wire 5 Typ* Max Units 90 25 Vrms Hz Test Conditions Superimposed on VBAT = -48V 3 200 ms 600 Ω Input Impedance at VR 100 kΩ 6 Output Impedance at Vx 10 Ω 7 Gain 2-wire to Vx -1.0 dB Gain relative to Gain @ 1kHz +0.1 Input 3dBm, 1kHz across Tip and Ring, 300-3400 Hz Gain VR to 2-wire -1.0 dB +0.15 dB (Input 1.0 Vrms 1kHz at VR ZLoad = 600Ω 300 - 3400 Hz 600Ω 20 30 dB Input 0.5 Vrms , 1kHz across Tip and Ring, ZLoad = 600Ω 20 30 dB Input 0.5 Vrms, 1kHz at VR ZLoad= 600Ω 50 55 dB Input 0.5 Vrms Input 3dBm, 1 kHz across Tip and Ring, Input 1.0 Vrms 1kHz at VR 8 Zin Gain relative to Gain @ 1kHz 9 2-wire Return Loss over 300-3400Hz 10 Transhybrid Loss 11 Longitudinal to Metallic Balance over 300-3400 Hz 12 Total Harmonic Distortion at Vx THL THD at Tip and Ring 13 Common Mode Rejection Ratio 2-wire to Vx 14 Idle channel Noise (at Vx) 15 Power supply rejection ratio VDD VEE VBat CMRR 40 Nc 0.1 1.0 % 0.1 1.0 % 50 dB 12 dBrnC Input 0.5Vrms, 1kHz C- Message PSRR 26 26 26 dB dB dB 1 VPP ripple, 1kHz on VDD/VEE/V BAT, measure at Vx and across Tip and Ring * Typical figures are at 25°C and are for design aid only. 2-111 MH88612 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) Notes: 1) Not to scale 2) Dimensions in inches). 3) (Dimensions in millimetres). *Dimensions to centre of pin & tolerance non accumulative. 0.05 + 0.01 (1.3 + 0.5) * 0.05 + 0.02 (1.3 + 0.05) * 0.020 + 0.05 (0.51 + 0.13) Figure 4 - Mechanical Data 2-112 * 0.18 + 0.02 (4.6 + 0.5) 0.100 + 0.10 (2.54 + 0.13)