MH88612K Subscriber Line Interface Circuit Preliminary Information Features ISSUE 3 April 1995 Ordering Information • Input impedance 600 Ω • 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 with diode protection • Power Denial • Wide V BAT Operating Range • Tip/Ring Reversal MH88612K 30 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, ringing feed and tipring reversal to the subscriber line, 2-Wire to 4-Wire hybrid interfacing, constant current feed and dial pulse detection. The device is fabricated as a thick film hybrid using various technologies. Applications Line interface for: • PABX • Intercoms • Key Telephone Systems • Control Systems LPGND VBat PD VDD VEE GNDA RF TF TIP Power Denial T/R Reverse Battery Feed RING RC2 RC1 VR Loop Supervision VRef VX Over Current Protection T/R Reverse Relay Driver VRLY RD1 2-Wire to 4-Wire Conversion Constant Current Feed Relay Drive Circuit RV CAP SHK Figure 1 - Functional Block Diagram 2-121 MH88612K Preliminary Information TF RF IC IC IC IC IC TIP IC RING RC2 LPGND IC VR VRef CAP SHK GNDA VEE VDD 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 TF VBat RV PD VX IC IC VRLY RC1 RD1 21 22 23 24 25 26 27 28 29 30 Figure 2 - Pin Connections Pin Description Pin # Name 1 TF Tip Feed. Connects to external diode for protection. Internally connected to pin 21. 2 RF Ring Feed (Input). is normally connected to ring relay for negative battery feed voltage and ringing voltage input. 3 IC/NC No Connections to be made to this pin, used for internal connection. 4 IC/NC No Connections to be made to this pin, used for internal connection. 5 IC/NC No Connections to be made to this pin, used for internal connection. 6 IC/NC No Connections to be made to this pin, used for internal connection. 7 IC/NC No Connections to be made to this pin, used for internal connection. 8 TIP 9 IC/NC No Connections to be made to this pin, used for internal connection. 10 RING Connects to the “Ring” lead of the telephone line. 11 RC2 Relay Control 2 (Input). Active high to reverse Tip/Ring. 12 LPGND 13 IC/NC 14 VR 15 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 25mA loop current. 16 CAP Connects external capacitor to ground for ring trip. 17 SHK Switch Hook Detect (Output). Active high 18 GNDA 19 VEE Negative Power Supply Voltage (-5V). 20 VDD Positive Power Supply Voltage (+5V). 21 TF 22 VBat 2-122 Description Connects to the “Tip” lead of the telephone line. Loop Ground is the system ground reference with respect to VBat. Normally tied with GNDA. No Connections to be made to this pin, used for internal connection. Voice Receive (Input) is the 4-wire analog signal to the SLIC. Analog Ground (0V) Tip Feed. Connect an external diode for protection. Internally connected to pin 1. Negative Battery Feed Supply Voltage (-48V). MH88612K Preliminary Information Pin Description (Continued) Pin # Name Description 23 RV Ring Feed Voltage connects to (RF) through a normally closed ring relay. 24 PD Power Denial (Input). A logic high will isolate the battery voltage to tip/ring. 25 Vx Voice Transmit (Output). is the 4-wire analog signal from the SLIC. 26 IC/NC No connections to be made to this pin, used for internal connection. 27 IC/NC No connections to be made to this pin, used for internal connection. 28 VRLY Relay Voltage Supply (+5V). This pin is used to power the on board relay. 29 RC1 Relay Control 1 (Input). Active high. Normally used for ringing. 30 RD1 Open collector sinks current when RC1 is at logic high. Functional Description The SLIC performs a transformerless 2-wire to 4wire 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 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: ILoop = 25 - V Ref 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. use of the relay K1. An internal clamp diode is provided between VRLY and RD1. 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 (Cap) to ground will provide adequate attenuation when ringing is applied. Once an off-hook condition has been detected a logic high should be applied to (RC) which will activate the relay (K1) to disconnect the ringing voltage from (RF) and reconnect to (RV). At that time 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 to 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. Tip/Ring Reverse The MH88612K provides a Tip/Ring reversal relay driver. To activate the internal relay to reversal Tip and Ring apply a logic input to RC2. Current Limit Ringing And Ring Trip Detection In Figure 3 a ringing signal (e.g., 90 Vrms +-48 Vdc is applied to the line by disconnecting (RV) from (RF), and connecting the ringing voltage at (RF) by The Tip or Ring may be accidentally shorted to ground. In such a case, current will only flow through the feed resistor. This high current will be sensed 2-123 MH88612K Preliminary Information and reduced by the current limit circuit to a lower value to protect the internal circuitry. subscriber loop. A logic high input applied to the power denial pin 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. This pin should be held low when not in use. Receive Gain The power denial function is a feature of the MH88612C which allows for powering down of the Applications Component List R1 = 1/4 W, + 10%, 200Ω R2 = 1/4 W, + 5%, 470Ω C1 = Cap. elec., 1.0µF, + 10%, 25V D1,D2,D3,D4 = Diode Rect., 200V, 1A, IN4003 K1 = 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 V RLY Options RV1, RV2 = 160V Vrms, 250V, 10J 90 VRMS SUPERIMPOSED ON -48VDC R1 VBat K1 MH88612K RF VR D4 RV D1 VX D2 TF D3 VRef VBat Tip TIP RV1 SHK RV2 RING Ring PD RC2 RC1 VRLY +5V C1 K1 VBat VDD -48V +5V VEE -5V Figure 3 - Application Circuit 2-124 Ring Trip Filter CAP RD1 GNDA + R2 Control MH88612K 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 1 Characteristics Sym Min Typ† Max Units Operating Supply Voltage VDD 4.75 5.0 5.25 V VEE -4.75 -5.0 -5.25 V 0 VRef VBat -27 Operating Temperatures TO -60 5 VRLY 2 -48 V 0 Comments Adjustable V V 70 °C † Typical figures are at 25°C and are for design aid only. 2-125 MH88612K Preliminary Information DC Electrical Characteristics* - Voltages are with respect to GNDA unless otherwise stated. Characteristics 1 Typ† Max Units Test Conditions IDD IEE IBAT 5.8 -2.6 500 mA mA µA PD = Logic high PC 210 1410 mW mW Standby Active 27 mA VRef = GNDA, V Bat = -48V 30 mA Adjustable with Ext. VRef Input, VBat = -48V 1200 Ω 40 mA 0.4 5.25 V V Sym Min Supply Current VDD VEE VBat 2 Power Consumption 3 Constant Current Line Feed ILoop 23 4 Adjustable Loop Current Range Operating Loop Resistance ILoop 18 5 Ring Ground Over-Current RLoop 6 Protection Off-Hook Detect 7 Output Low Voltage (On-hook) Output High Voltage (Off-hook) Off- Hook Detect VOL VOH Output Low Current (on-hook) Input High Current. (off-Hook) RC1,RC2, PD Control Inputs IOL IOH 8 -400 mA µA Input Low Volt. (no activation) Input High Volt. (activation) RC1, RC2, PD control Inputs VIL VIH 0.7 V V Input Low Current (no activation) Input high current (activation) IIL IIH -50 50 µA µA 8 9 10 25 Active high logic 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. 2-126 VBat = -28V @ ILoop = 18mA, R Loop includes telephone set MH88612K Preliminary Information AC Electrical Characteristics Characteristics Sym Min Typ* Max Units 40 17 80 110 25 Vrms Hz 1 Ringing Voltage VRING 2 Ringer Equivalence Number REN 3 Ring Trip Detect time 4 Input AC Impedance 2-wire 5 Test Conditions Superimposed on VBAT = -48V 3 100 125 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 Input 3 dBm, 1kHz across Tip and Ring, 300-3400 Gain relative to Gain @ 1kHz +0.1 Gain VR to 2-wire -1.0 dB +0.25 dB (Input 1.0 Vrms 1kHz at VR ZLoad = 600Ω 300-3400 Hz) 20 30 dB Input 0.5 Vrms 1kHz across Tip and Ring, ZLoad = 600Ω 35 50 dB Input 0.5V Vrms 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 over 300-3400 Hz 11 Longitudinal to Metallic Balance 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 0.1 1.0 % 0.1 1.0 % 50 Nc dB 12 dBrnC Input 0.5 Vrms, 1KHz C- Message PSRR 30 30 30 35 40 60 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. 2-127 MH88612K Preliminary Information 3.000 + 0.020 0.020 Max (0.5 Max) Side View (76.2 + 0.5) 0.527+0.020 (13.4 + 0.5) 0.010 + 0.002 (0.25 + 0.05) 0.34 Max (8.5 Max) * 0.05 + 0.02 (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. * 0.15 + 0.02 (3.81 + 0.5) Figure 4 - Mechanical Data 2-128 0.100 + 0.010 (2.54 + 0.26) 0.180 + 0.02 (4.6 + 0.5)