MH88612C Subscriber Line Interface Circuit Preliminary Information Features ISSUE 4 April 1995 Ordering Information • Input impedance 200Ω + 560Ω // 0.1µF • 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 VBat Denial • Wide Operating Range • Programmable Receive Gain MH88612C 20 Pin SIL Package 0°C to 70°C Description The SLIC provides a complete interface between a switching system and 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 VBat VDD VEE GNDA TF TIP RING RF Current & Voltage Sensing RV RD 2-Wire to 4-Wire Conversion VR VX Over Current Protection VRLY RC GS Relay Drive Circuit Constant Current Feed Loop Supervision VRef CAP SHK FIgure 1 - Functional Block Diagram 2-113 MH88612C Preliminary Information IC TF IC VR VRef VEE GNDA GS VX TIP RING RF VDD RC RD RV VRLY IC VBat CAP SH K 0 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 0 IC Internal Connection. No pin fitted in this position. 1 TF Tip Feed. Connects to external diode to LPGND for protection. 2 IC Internal Connection. No pin fitted in this position. 3 VR Voice Receive (input) is the 4 wire analog signal to the SLIC. 4 VRef Voltage Reference 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 21mA loop current. 5 VEE Negative Power Supply voltage. (-5V). 6 GNDA 7 GS Gain setting (Input). A logic low at this input adds an additional -0.5dB gain in the receive direction. This gain is in addition to the gain set by the Codec. A high adds 0dB gain. 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 11 RF 12 VDD 13 RC Relay Control (Input). Active high will apply ringing to the line. 14 RD Output Drive Sources current when RC is at a logic high. 15 RV Ring Feed Voltage connects to pin 11 (RF) through a normally closed relay contact. 16 VRLY 17 IC 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. 2-114 Description Analog Ground. (0V) Connects to the “Ring” lead of the telephone line. Ring Feed (Input). is connected via the ring relay to either negative battery feed voltage, (RV), or ringing voltage input. Positive Power Supply Voltage. (+5V) Relay voltage Supply. (+5V) Internal Connection. No pin fitted in this position. MH88612C 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 21mA. For a constant current setting between 18mA and 30mA, VRef can be set between -8.75 Vdc and -6.35 Vdc. The relationship is detailed in the formula below: ILoop = [-2.6(VRef) + 21.5] mA +2mA 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 (e.g. 90 Vrms superimposed on -48 VDC) is applied to the line by disconnecting pin 15 (RV) from pin 11 (FR), and connecting the ringing voltage at pin 11 (RF) by use of the relay K1. For applications requiring dial pulse detection the capacitor connection to ground should be controlled so 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 to system drive output of a codec. Applying GNDA to 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. Once an off-hook condition has been detected a logic low on the Relay Control (RC) input deactivates the relay (K1) to disconnect the ringing voltage from pin 11 (RF)and reconnect to pin 15 (RV). At that time the SLIC will revert to constant current feed operation. 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. Receive Gain The MH88612C Receive Gain (VR to 2-wire) can be adjustable by -0.5dB if GS is taken logic low or by 0dB if GS is taken logic high. When the MH88612C issued with an off hybrid MT896x codec the Receive Gain can be set to either -3.5dB or -7dB by writing to control Register A of Codec and programming GS appropriately. 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 1µF capacitor connected from pin 19 (CAP) to ground will provide adequate attenuation when ringing is applied. 2-115 MH88612C Preliminary Information Applications Component List R1 R2, C1 D1,D2 K1 = 1/4 W, + 10% 200Ω = 1/4W, ±5%, 470KΩ = 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 VDD, V EE, VBat, VRef and V RLY. Options RV1, RV2= 160 Vrms, 250V 10J 90 VRMS SUPERIMPOSED ON -48VDC VBat R1 K1 11 D4 15 MH88612C RF 3 RV VR D1 D2 1 TF D3 VX 8 VBat 4 TIP VRef 9 RV1 20 SHK RV2 10 RING 7 GS RC 13 VRLY +5V 16 K1 14 RD CAP VBat VDD 18 -48V 12 +5V VEE GNDA 5 6 -5V Figure 3 - Application Circuit 2-116 C1 19 - + R2 Ring Trip Filter Control MH88612C Preliminary Information Absolute Maximum Ratings* Parameter Symbol Min Max Units 1 DC Supply Voltage VDD VEE VBat -0.3 +0.3 0.3 +15 -15 -60 V V V 2 Storage Temperature TSTG -40 100 °C 3 Package Power Dissipation 2 w PD * 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* 4.75 5.0 5.25 V VEE -4.75 -5.0 -5.25 V VBat 0 -27 -60 V 70 °C 5 Adjustable V 0 TO Comments V -48 VRLY Operating Temperature Units VDD VRef 2 Max * Typical figures are at 25°C and are for design aid only. DC Electrical Characteristics† - Voltages are with respect to GNDA unless otherwise stated. Characteristics 1 Sym Min Typ* Max Units IDD IEE IBAT 0.8 0.5 0.0 5 3 2 12 10 2.5 mA mA mA Idle State mW mW Standby Active 24 mA VRef = GNDA, V Bat = -48V 30 mA Adjustable with Ext. VRef input, VBat = -48V 1850 Ω VBat = -48V @ I Loop = 18mA, RLoop includes telephone set 40 mA 0.4 5.25 V V Supply Current VDD VEE VBat 210 1410 2 Power Consumption 3 Constant Current Line Feed ILoop 18 4 Adjustable Loop Current Range ILoop 18 5 Operating Loop Resistance RLoop 6 Ring Ground Over-Current protection 7 Off-Hook Detect Output Low Current (On-hook) Output High Current (Off-hook) VOL VOH Off- Hook Detect Output Low Current (on-hook) Input High Current. (activation) IOL IOH 8 -400 mA µA RC Control Input Input Low Volt. (no activation) Input High Volt. (activation) VIL VIH 0.7 V V IIL -50 µA IIH 50 µA 8 9 10 Test Conditions RC control Input Input Low Current (no activation) Input high current (activation) PC 21 Active high logic 0.0 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. 2-117 MH88612C Preliminary Information AC Electrical Characteristics Characteristics Sym Min 40 1 Ringing Voltage VRING 2 Ringer Equivalence Number REN 3 Ring Trip Detect time 4 Input AC Impedance 2-wire (1) 5 6 7 Max Units 90 25 Vrms Hz ms 719 Ω Input Impedance at VR 100 kΩ Output Impedance at VX 10 Ω Gain 2-wire to VX 0 dB Zin -0.5 -0.22 0.1 0.1 dB dB Gain VR to 2-wire Superimposed on VBat =-48V @1020Hz Input 3 dBm, 1kHz across Tip and Ring, 300Hz & 3k4Hz 600Hz & 2k4Hz ZLoad See Note (1). Input 1.0Vrms, 1kHz @ VR -0.6 -0.4 dB dB with GS @ at logic high with GS @ at logic low -0.5 0.22 0.1 0.1 dB dB 300Hz & 3k4Hz 600Hz & 2k4Hz ZLoad, See Note (1). 0 Gain relative to Gain @ 1kHz with GS @ logic high 9 2-wire Return Loss over 300-3400Hz 10 Transhybrid Loss over 300-3400 Hz 11 Longitudinal to Metallic Balance over 300-3400 Hz 12 Total Harmonic Distortion at VX THL 20 30 dB Input 0.5 Vrms , across Tip and Ring, ZLoad = complex network. See Note (1). 20 35 dB Input 0.5V Vrms, ZLoad= complex network. See Note (1). 46 55 dB Input 1 Vrms % Input 3dBm, 1 kHz across Tip and Ring, Input 1.0 Vrms 1kHz at VR THD at Tip and Ring 13 Common Mode Rejection Ratio 2-wire to VX 14 Idle channel Noise (at VX) CMRR 40 0.1 1.0 0.1 1.0 50 Nc Power supply rejection ratio VDD VEE VBat % dB 14 -76 12 -78 (at T & R) 15 Test Conditions 3 100 Gain relative to Gain @ 1kHz 8 Typ* dBrnC dBrnp dBrnC dBrnp Input 1 Vrms, 1KHz C- Message psophemetric C- Message psophometric PSRR 20 20 20 30 30 30 dB dB dB 1 VPP ripple, 1kHz on VDD/VEE//VBat,measure at Vx and across Tip and Ring * Typical figure are at 25°C and are for design aid only: not guaranteed and not subject to production testing. Note (1): Zin = 200 + 560Ω //0.1µF 2-118 MH88612C Preliminary Information 0.080 Max (2.0 Max) Side View 2.13 Max (54.34 Max) 0.6 Max (15.3 Max) 20 1 0.010 + 0.002 (0.25 + 0.05) 0.05 + 0.02 (1.3 + 0.5) 0.27 Max (6.9 Max) * * 0.025 Max Notes: 1) Not to scale 2) Dimensions in inches). 3) (Dimensions in millimetres). *Dimensions to centre of pin & tolerance non accumulative. * 0.15 + 0.02 (3.81 + 0.5) 0.020 typ 0.180 + 0.02 (4.6 + 0.5) 0.100 + 0.010 (2.54 + 0.26) Figure 4 - Mechanical Data 2-119 MH88612C Notes: 2-120 Preliminary Information