MH88631 Central Office Interface (LS/GS) Preliminary Information Features ISSUE 4 Ordering Information • Transformerless 2-4 wire conversion • Line state detection outputs • - forward current • - reverse current • - ring ground • - tip ground • - ringing voltage • Programmable audio transmit and receive gain • Loop start or ground start termination • Selectable 600Ω or AT&T compromise balance network • -1 version: 20Hz Ringing Voltage • -2 version: 50Hz Ringing Voltage MH88631-1 MH88631-2 PBX • Channel bank • Intercom • Key System RG FC RV RC TG T R 40 Pin SIL Package 40 Pin SIL Package 0°C to 70°C Applications • Signal Detection Circuitry Description The Mitel MH88631-1, 2 Central Office Trunk Interface circuit provides a complete audio and signalling link between audio switching equipment and a central office. The loop seize circuitry is controlled by an external input to provide either a loop start of ground start termination. The device is fabricated using thick film ceramic technology to achieve high density circuit design. LPGND RINGND VCC+ VCC- AGND Ring Ground Relay Driver 1 RC1 RD1 RGND Relay Driver 2 CD RD2 RC2 Network Balance VTR+ VTRRXINRXIN+ April 1995 NETBAL Audio Section Circuitry (2-4 Wire) Active Termination QB QE XA XB XC VDD VEE RXOUT GSX VX VR GSR TXIN+ TXIN- Figure 1 - Functional Block Diagram 2-225 MH88631 Preliminary Information LPGND VDD RINGND T R VTRVTR+ XC XA QE AGND RXIN+ RXINVEE TG RC RV FC RG QB 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 XB VEE VDD RXOUT VCC+ GSR TXINVCCTXIN+ AGND VR VX RGND GSX RC1 NETBAL RD1 CD RD2 RC2 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Figure 2 - Pin Connections Pin Description Pin # Name 1 LPGND 2 VDD 3 RINGND 4 T Tip (Input). Normally connects to the “Tip” lead of the C.O. 5 R Ring (Input). Normally connects to the “Ring” lead of the C.O. 6 VTR- Connects to the TXIN+ (Pin 29) via an external capacitor (C1). 7 VTR+ Connects to the collector of an external transistor (Q1) and TXIN- (Pin 27) via an external capacitor (C4) 8 XC External relay contact (K1) connection from XB (Pin 21), activates by loop seize control input (RC1). 9 XA External relay contact (K1) connection from VTR+ (Pin 7), activated by loop seize control input (RC1). 10 QE Connects to the emitter of an external transistor (Q1). 11 AGND Analog Ground. 12 RXIN+ Differential Receive (Input). Connects to analog ground via an external capacitor (C2). 13 RXIN- Differential Receive (Input). Connects to RXOUT (Pin 24) via an external capacitor (C3). 14 VEE 15 TG Tip Lead Ground Detect (Output). Active low. 16 RC Reverse Loop Current Detect (Output). Active low. 17 RV Ringing Voltage Detect (Output). Active low. 18 FC Forward Loop Current Detect (Output). Active low 19 RG Ring Lead detect (Output). Active low. 20 QB Connects to the base of an external transistor (Q1). 2-226 Description Loop Ground is the system ground reference with respect to -48V. Positive Power Supply (+5V). Ring Ground (Input). For Ground Start Trunk only a logic low input will enable the trunk circuit to ground the Ring lead through a low resistance (390Ω). This is a signal to the C.O. that the interface is seizing the line. Negative Power Supply. (-5V). MH88631 Preliminary Information Pin Description (Continued) Pin # Name Description 21 XB External relay contact (K1) connection from XC (Pin 8), activated by loop seize control input (RC1). 22 VEE Negative Power Supply. (-5V). 23 VDD Positive Power Supply. (+5V) 24 RXOUT 25 VCC+ Positive analog Power Supply Voltage. (+12V). 26 GSR Gain Setting Receive (Input). Normally used to set the receive gain with an external resistor connected to RXOUT (Pin 24). 27 TXIN- Transmit (Input). Differential audio signal from VTR- (Pin 6), via an external capacitor (C4). 28 VCC- Negative Analog Power Supply Voltage. (-12V). 29 TXIN+ Transmit (Input). Differential audio signal from VTR- (Pin 6), via an external decoupling capacitor (C1). 30 AGND Analog Ground. 31 VR Audio Receive (Input). The four-wire audio signal input to the interface. 32 VX Audio Transmit (Output). The four-wire audio signal output from the interface. 33 RGND 34 GSX Gain Setting Transmit (Input). Normally used to set the transmit gain with an external resistor connected to VX (Pin 32). 35 RC1 Relay Control 1 (Input). A logic high will activate the relay (K1) to provide loop seize across Tip and Ring. 36 NETBAL 37 RD1 Relay Driver 1 (Output). Open collector sinks current when RC1 is high. Diode clamp protected. 38 CD Clamping Diode. Normally connects to the positive supply voltage. 39 RD2 Relay Driver 2 (Output). Open collector sinks current when RC2 is high. Diode clamp protected. 40 RC2 Relay Driver 2 (Input). A logic high will activate the relay (K2) to provide proper biasing to the Tip and Ring. This input control is used for Ground Start Trunk only. Audio receive signal (output) tothe RXIN- (Pin 13), via an external decoupling capacitor (C3). Relay Ground. Network Balance (Input). When there is no connection (open), the network is balanced at 600Ω. When the pin is grounded, the network is balanced at AT&T compromise. 2-227 MH88631 Functional Description The MH88631-1, 2, is a Central Office Loop Start and/or Ground start analog Trunk interface circuit providing a complete audio and signalling link to the Central Office. The trunk interface circuit performs transformerless 2 to 4 wire conversion, between the 2-wire telephone loop and the 4 wire transmit and receive pairs of a voice switching system. The 4-wire connection can be interfaced to a filter/ codec, such as the MT896X, for use in a digital voice switched system. Voiceband analog signals, coming for the C.O., applied differentially across Tip and Ring, pass through a bridge rectifier and appear at VTR+ and VTR- where they are actively terminated. Refer to Fig. 3 - Application Circuit. External capacitors C1 and C4 couple the incoming signals into the balanced input of the Transmit audio circuitry via TXIN+ and TXIN-. The transmit gain is adjusted by feedback resistor R4. For best performance R4 should be physically located as close as possible to the GSX pin. The gain adjusted transmit signal appears at the Vx output pin. Relay K1 is the loop seize which applies active line termination and also provides biasing of the current modulator circuitry. Activating and deactivating K1 provides dial pulsing. Q1 is the current modulator output transistor, referred to as the loop driver transistor. Outgoing analog signals from the system are provided to the interface at the VR input where they enter an amplifier section with the gain controlled by the selection of the Rx gain feedback resistor R3. For best performance, R3 should be physically located as close as possible to the GSR pin. The output of the amplifier, RXOUT, is coupled to RXIN-, the current modulator circuitry, via C3. The balanced input to the current modulator is completed with the connection of C2 from RXIN+ to ground. Transmission to the C.O. is accomplished by modulating the loop with the outgoing analog signals. To ensure that the transmitted signals are not coupled to the receive circuitry, transhybrid loss is maximised. The impedance matching, performed by the balance network reduces power loss and signal reflections. The network balance input, NETBAL, of the interface’s 2-wire to 4-wire convertor circuitry provides selection of a 600Ω balance, used when feeding channel banks or when performing external tests on the trunk circuit, or the AT&T compromise. When the NETBAL input pin is grounded, the interface balance against the AT&T 2-228 Preliminary Information compromise network consisting of 350Ω plus 1kΩ shunted by a 0.21µF capacitor. This is typical of North American C.O. connections. The Tip and Ring also provide the balanced input to the signal detection circuitry which generates the signalling status outputs TG, RC, RV, FC and RG. For Ground Start signalling, relay K2 and resistor R1 and R2, are required. Activation of K2 is controlled by the relay control logic input signal, RC2. In the idle state, K2 is closed connecting the -48 VDC supply Tip and Ring through biasing resistors R1 and R2. Upon detection of TG or RG, the system then pulls RC1 low, closing K1, then pulls RC2 low which opens K2 to remove the -48 volts supply from Tip and Ring. In the Ground Start signalling environment, initiating a call to the C.O. is performed by the following sequence of events. The system provides a logic low on the ring ground input pin of the interface. This activates the circuitry which grounds the ring lead through a current limiting resistance. The C.O. recognizes the ground condition and connects the tip lead to ground. The interface senses this condition and the tip lead ground detect output switches to a logic low. The system then applies active line termination by closing K1 using RC1 and opens K2 using RC2. A call from the C.O. can be performed similarly. The C.O. can signal to the interface by pulling either Tip or Ring to ground potential, or by applying ringing voltage to the Ring lead. Signal Detection Circuitry The signal detection circuitry provides the signalling status outputs. The system, controlling the interfaces, monitors these active low logic outputs. RV is the Ringing Voltage detect outputs. When the C.O. applies ringing voltage to the termination, the trunk interface provides a 50ms debounced output at RV during the ringing burst period. This output will remain low for approximately 50ms after C.O. removes the ringing Voltage. Ringing voltage above 40 VRMS at 20Hz will be detected. TG is the Tip lead Ground detect output and RG is the Ring lead Ground detect output. The TG and RG outputs provides a means of determining call original or other hand shaking functions. The high impedance detection circuitry of the interface will detect both Tip and Ring Ground voltages above approximately -15.3V of true ground. RC is the Reverse Loop Current detect output and FC is the Forward Loop Current detect output. MH88631 Preliminary Information The RC and FC outputs of the interfaces are used to determine the polarity of the Tip and Ring pair which the C.O. uses for signalling during the active (off-hook) state of the interface. When the loop is closed by the interface, the trunk is in the normal or unreversed state. Some C.O.’s may reverse the polarity of Tip and Ring, to indicate the talking state. The interface will detect this condition and RC will output a low level. and Ring inputs of the interface, following by metal oxide varistors from Tip and Ground, Ring to Ground and Tip to Ring. Components List (for Figure 3) R1*, R2* R4 External Circuitry Requirements R3 The loop seize circuit is completed with the addition of external components Q1, C5, R5 and K1. K1, a DPST reed relay, is activated by relay control signal RC1. When the loop seizure is required, K1 is closed and the interface applies active termination across Tip and Ring. The relay should have a 0.5 amp contact capability and 12 VDC operation with a typical 500Ω coil resistance. To prevent back EMF from damaging the relay drive transistor, (caused by the collapsing field of the inductive coil of the relay) a snubbing diode is provided on the hybrid and therefore not required externally. C5 and R5 provide relay contact noise filtering and transient noise suppression necessary for clamping inductive spikes created when the loop is closed during line seizure or dial pulsing. = 30.9kΩ, ± 1% 1/4W = Transmit Gain Adjust Resistor = 301.5 E3x Gain VX - 100 E3 VTR Typical Value = 200kΩ, ± 1% 1/4W = Receive Gain Adjust Resistor = 523.2 E3 x Gain VTR VR Typical Value = 505kΩ, ± 1%, 1/4W R5 = 510Ω, ± 5%, 1/4W R6 = 10kΩ, ± 5%, 1/4W C1, C2, C3, C4= 0.22µF, ± 10%, 200V C5 = 0.1µF, ± 5%, 250V C6 = 1.0µF, ± 5%, 250V Q1 = 2N5657, NPN 350V, 0.5A, 20W K1, K2 = 2A Reed Relay, E/M 12V 2 Form C Dip *Note: required for Ground Start applications, not required for Loop start applications. Q1 provides current drive for the active termination, controlling the loop current flow of the current modulator circuitry. Selection of a suitable transistor for Q1 is made based on worst case conditions which include fault conditions. A 350 volt, or higher, rating for Q1 is necessary to meet high voltage requirements. The Tip and Ring input protection varistors limit any high voltage spikes to approximately 300 volts. Under worst case conditions Q1 must be able to handle close to 100mA of collector current and dissipate two watts continuously. During pulse dialling, current spikes are generated due to the inductive nature of the loop. A 0.5 amp continuous connector current rating is therefore recommended to provide a safe margin. K2, R1 and R2 are required only for Ground Start applications. K2 is the same type of relay as K1 and is activated by RC2. Once again the snubbing diode is provided on the hybrid. R1 and R2 provide the -48V biasing the signalling (on-hook) state. R6 and C6 constitute the Dummy Ringer required for the LS/GS trunk. These components are also part of the 600Ω input impedance. Protection circuitry on the Tip and Ring inputs may be required depending upon the trunk interface application. For maximum protection it is recommended to place fuses in series with the Tip 2-229 MH88631 Preliminary Information Absolute Maximum Ratings* Parameter 1 2 DC Supply Voltage Sym Min Max Units VDD - GNDD VEE - GNDD VCC + -GNDA VCC - GNDA -0.3 -0.6 +6.0 +0.3 +18.0 +18.0 V V V V TSTG -55 +125 °C Storage Temperature * Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied. Recommended Operating Conditions Parameter Sym Typ* Min Max Units VDD VEE VCC+ VCC VBat 4.75 -5.25 11.4 -11.4 5.0 -5.0 12.0 12.0 -48 5.25 -4.75 12.6 -12.6 V V V V V 1 Operating Supply Voltage 2 Operating Current IDD IDD IDD IDD 6.0 -6.0 8.0 -8.0 mA mA mA mA 3 Power Consumption PC 265 mW 70 °C 0 Operating Temperature TOP * Typical figures are at 25° C with nominal + 5V supplies for design aid only. 4 Comments RINGND high DC Electrical Characteristics‡ Characteristics Sym Min 1 Input High Voltage RC1, RC2 RINGND VIH 2.7 4.5 2 Input High Current RC1, RC2 RINGND IIH 2.5 3 Input Low Voltage RC1, RC2 RINGND VIL RC1, RC2 RINGND IIL 4 Input Low Current Typ* Max Units Test Conditions V V 5.0 -100 mA µA 0.7 V 1.0 1.1 µA mA ‡ DC Electrical Characteristics are over recommended operating conditions unless otherwise stated. * Typical figures are at 25°C with nominal +5V supplies and are for design aid only. Control Inputs State Table Parameter Active Idle 1 RC1 Logic high Logic Low 2 RC2 Logic High Logic Low 3 RINGND Logic Low Logic High 4 NETBAL AT&T compromise network (350Ω + 1kΩ/0.2µF) 600Ω network 2-230 AGND Open (no connection) MH88631 Preliminary Information AC Electrical Characteristics Characteristics 1 Ringing Voltage 2 Ringing Frequency Sym Min Typ* Max Units VR 40 90 130 Vrms -1 version 20 Hz -2 version 50 Hz 3 Operating Loop Current IL 4 Off-Hook DC Resistance 5 Operating Loop Resistance 6 On-Hook Leakage Current 7 Ring Ground Sink Current 8 Tip and Ring AC Impedance 9 Longitudinal Balance metallic to longitudinal 18 Test Conditions Voltage range 40 -120Vrms Voltage range 35 -120Vrms 70 mA RT 300 Ω @18mA RL 2300 Ω @18mA µΑ RINGND = 5.0Vdc mΑ -48VDC with 200Ω in series on Ring lead Ω with 1.0kΩ + 1.0µF in parallel with Tip and Ring 60 40 58 53 dB dB dB dB 200-1000Hz 1000-4000Hz 200-1020Hz 1020-3020Hz 20 26 30 dB dB dB 200-500Hz 500-1000Hz 1000-340Hz 3 IRG 100 600 longitudinal to metallic 10 Return Loss Trunk to Line 11 Transhybrid Loss (single frequency) into 600Ω THL 18.5 34 30 dB dB dB 200Hz 1000Hz 3000Hz 12 Transhybrid Loss (single frequency) into AT&T Compromise THL 18 20 dB dB 200-1000Hz 1000-4000Hz 13 Frequency response (Output relative to 1kHz, VTR/VR and VX/VTR) dB dB dB dB 200Hz 300Hz 3000Hz 3400Hz -0.15 -0.10 -0.10 -0.15 0.05 0.05 0.05 0.05 See Note 1 14 Idle channel noise 15 Power Supply rejection ratio 16 Analog signal overload level (adjustable gain) PSR R 8 dBrnco 40 dB 6 dBm C-Message 1kHz,0dBm = 0.775Vrms into 600Ω * Typical figure are at 25°C with nominal ±5V supplies and are for design aid only Note 1: Input 0dBm at VTR, or input 0.0775Vrms at VR. TR=600Ω Termination. DC Electrical Characteristics Characteristics 1 Sym Min Typ* Max Units Test Conditions No Load on output Output High Voltage (TG, RC, RV, FC, RG) 4.75 V Output High Current (TG, RC, RV, FC, RG) 0.17 mA 3 Output Low Voltage (TG, RC, RV, FC, RG) -0.30 V 4 Output Low Sink Current (TG, RC, RV, FC, RG) -0.40 mA 2 VOH=-2.7Vdc No Load on output VOL=-0.4Vdc * Typical figure are at 25°C with nominal ±5V supplies and are for design aid only 2-231 MH88631 Preliminary Information MH88631-1, -2 DUMMY RINGER TIP 4 LIGHTNING VTRT TXIN+ R6 PROTECTION C6 RXIN+ 5 RING R1 RXINRXOUT K2A AGND GSR K2B -48V RETURN 1 LPGND -48V BATTERY Loop Current Setting 33 RGND 40 +12V K2 39 38 K1 37 35 16 17 18 19 15 RC2 XB XC XA CD RD1 RC1 NETBAL RC RINGND RV VR FC VX RG GSX TG +5V 13 C3 24 26 R3 K1A 21 8 K1B 9 C4 C5 Q1 36 3 31 32 VEE VCC+ VCC- 2,23 22,14 -5V 25 28 +12V -12V Figure 3 - Application Circuit 2-232 12 C2 27 TXIN 7 VTR+ 20 QB 10 QE RD2 VDD C1 29 R R2 11,30 6 34 R4 R5 MH88631 Preliminary Information 0.140 Max (3.6 Max) Side View 4.00 + 0.03 (102 + 1.0) 0.60 Max (15.25 Max) 1 2 3 4 39 40 0.010 + 0.002 (0.25 + 0.05) 0.14 Max (3.6 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) * 0.18 + 0.02 (4.6 + 0.5) 0.100 + 0.10 (2.54 + 0.13) Figure 4 - Mechanical Data 2-233 MH88631 Notes: 2-234 Preliminary Information