MH88630 Central Office Interface (LS/GS) Preliminary Information Features ISSUE 7 • Transformerless 2-4 Wire conversion • Line state detection outputs: - Ordering Information MH88630 forward current reverse current ring ground tip ground ringing voltage 40-Pin DIL Package 0°C to 70°C Description • Programmable audio transmit and receive gain • Loop start or ground start termination • Selectable 600Ω or AT&T compromise balance network Applications • • • • April 1995 The Mitel MH88630 Central Office Trunk Interface circuit provides a complete audio and signalling link between an audio switching equipment and a central office. The loop seize circuitry is controlled by an external input to provide either a loop start or ground start termination. The device is fabricated using thick film hybrid technology to achieve high density circuit design. PBX Interface to Central Office Channel bank Intercom Key system RG FC T R RV RC TG LPGND RINGND VCC+ VCC- AGND Ring Ground Relay Driver 1 Signal Detection Circuitry Relay Driver 2 VTR+ VTRRXINRXIN+ Network Balance Active Termination QB QE XA XB GSX VX VR GSR Audio Section Circuitry (2 - 4 Wire) XC VDD VEE RXOUT TXIN+ RC1 RD1 RGND CD RD2 RC2 NETBAL TXIN- Figure 1 - Functional Block Diagram 2-215 MH88630 Preliminary Information IC T R IC IC LPGND RINGND VTR+ QE QB VTRXA XB XC RGND RC1 RD1 CD RD2 RC2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 RG FC RV RC TG VDD VEE AGND RXINRXIN+ NETBAL VX GSX TXIN+ TXINVCCVCC+ RXOUT GSR VR Figure 2 - Pin Connections Pin Description Pin # Name 1 IC Internal Connection. Pin cut short. Leave open circuit. 2 T Tip (Input). Normally connects to the “Tip” lead of the C.O. 3 R Ring (Input). Normally connects to the “Ring” lead of the C.O. 4 IC Internal Connection. Leave open circuit. 5 IC Internal Connection. Leave open circuit. 6 LPGND Loop Ground is the system ground reference with respect to -48 volts. 7 RINGND 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. 8 VTR+ 9 QE Connects to the emitter of an external transistor (Q1). 10 QB Connects to the base of an external transistor (Q1). 11 VTR- 12 XA External relay contact (K1) connection from VTR+ (pin 8), activated by loop seize control input (RC1). 13 XB External relay contact (K1) connection from XC (pin 14), activated by loop seize control input (RC1). 14 XC External relay contact (K1) connection from XB (pin 13), activated by loop seize control input (RC1). 15 RGND 16 RC1 Relay Control 1 (Input). A logic high will activate the relay (K1) to provide loop seize across Tip and Ring. 17 RD1 Relay Driver 1 (Output): Open collector sinks current when RC1 is high. Diode clamp protected. 18 CD Clamping Diode: Normally connects to the positive supply voltage. 2-216 Description Connects to the collector of an external transistor (Q1) and TXIN - (pin 26) via an external capacitor. Connects to the TXIN+ (pin 27), via an external capacitor (C1). Relay Ground. MH88630 Preliminary Information Pin Description (Continued) Pin # Name Description 19 RD2 Relay Driver 2 (Output): Open collector sinks current when RC2 is high. Diode clamp protected. 20 RC2 Relay Control 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. 21 VR 22 GSR 23 RXOUT 24 VCC+ Positive analog Power Supply Voltage (+12V). 25 VCC- Negative analog Power Supply Voltage (-12V). 26 TXIN- Transmit (Input). Different audio signal from VTR+ (pin 8), via an external capacitor (C4). 27 TXIN+ Transmit (Input). Different audio signal from VTR- (pin 11), via an external decoupling capacitor (C1). 28 GSX Gain Setting Transmit (Input). Normally used to set the transmit gain with an external resistor connected to VX (pin 29). 29 VX 30 NETBAL Network Balance (Input). When there is no connection (open), the network is balanced at 600Ω. When this pin is grounded, the network is balanced at AT&T compromise. 31 RXIN+ Differential Receive (Input). Connects to analog ground via an external capacitor (C2). 32 RXIN- Differential Receive (Input). Connects to RXOUT (pin 23) via an external capacitor (C3). 33 AGND Analog Ground. 34 VEE Negative Power Supply (-5V). 35 VDD Positive Power Supply (+5V). 36 TG Tip Lead Ground Detect (Output). Active low. 37 RC Reverse Loop current Detect (Output). Active low. 38 RV Ringing Voltage Detect (Output). Active low. 39 FC Forward Loop Current Detect (Output). Active low 40 RG Ring Lead Ground Detect (Output). Active low. Audio Receive (Input). The 4-wire audio signal input to the interface. Gain Setting Receive (Input). Normally used to set the receive gain with an external resistor connected to RXOUT (pin 23). Audio receive signal (output) to the RXIN- (pin 32), via an external decoupling capacitor (C3). Audio Transmit (Output). The 4-wire audio signal output from the interface. 2-217 MH88630 Functional Description The MH88630 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 from 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 receive audio circuit via TXIN+ and TXIN-. The receive 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 receive signal appears at the Vx output pin. Relay K1 is the loop seize relay which applies active line termination and also provides biasing of the current modulator circuit. Activating and deactivating K1 provides dial pulsing. Q1 is the current modulator output transistor, referred to as the loop drive transistor. Outgoing analog signal 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 Tx 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 balanced network reduces power loss and signal reflections. The network balance input, NETBAL, of the interface’s 2-wire to 4-wire converter circuitry provides selection of a 600Ω balance, used when feeding channel banks or when performing external 2-218 Preliminary Information tests on the trunk circuit, or the AT&T compromise. With the NETBAL input pin left the interface is balanced to match to 600Ω. If the NETBAL input pin is grounded, the interface is balanced against the AT&T compromise network consisting of 350Ω plus 1kΩ shunted by a 0.21µF capacitor. This is intended for typical North American C.O. connections. The Tip and Ring also enter the balanced input of the signal detection circuitry which provides 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 -48Vdc supply to Tip and Ring through biasing resistors R1 and R2. Upon detection of TG or RG, the system them pulls RC1+ low closing K1, then pulls RC2 low which opens K2 to remove the -48V volts supply from Tip and Ring. In the Ground Start signalling environment, initiating a call to the C.O. is preformed by the following sequence of events. The system provides a logic low on the ring ground input pin of the interface. This activates the circuit which grounds the ring lead through a current limiting resistance. The C.O. recognises 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 circuit provides the signalling status output. The system, controlling the interface, monitors these active low logic outputs. RV is the Ringing Voltage detect output. When the C.O. applies ringing voltage to the termination, the trunk interface provides a 50ms debounced outputs at RV during the ringing burst period. This output will remain low for approximately 50ms after the C.O. removes the ringing voltage. Ringing voltage above 40 VRMS at 20 Hz 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 provide a means of determining call origination or other handshaking functions. The high MH88630 Preliminary Information impedance detection circuitry of the interface will detect both Tip and Ground and Ring Ground voltages above approximately -15.3V of true ground. RC is the Reverse loop current detect output and FC if the Forward loop Current detect output. The RC and FC outputs of the interface 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. 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. A protection circuit 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 and Ring inputs of the interface, following by metal oxide varistors from Tip and Ground, Ring to Ground and Tip to Ring. External Circuitry Requirements Components List (for Figure 3) The loop seize circuit is completed with the addition of external components Q1, C5, R5 and K1. R1*, R2 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. 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. = 30.9kΩ, ± 1%, ¼ W = Receive Gain Adjust Resistor = 523.2 E3 x Gain VTR/VR Typical Value = 505kΩ, ±1%, ¼ W R3 = Transmit Gain Adjust Resistor = 301.5 E3 x Gain VX/VTR-100 E3 Typical Value = 200kΩ, ± 1%, ¼ W R5 = 510Ω, ± 5%, ¼ W R6 = 10kΩ, ± 5%, ¼ W C1, C2, C3, C4 = 0.22µF, ± 10%, 200V C5 = 0.1µF, ± 5%, 250V C6 = 1.0µF, ± 5%, 250V Q = 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. 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 2-219 MH88630 Preliminary Information Absolute Maximum Ratings* - Voltages are with respect to AGND. Parameters 1 DC Supply Voltages Sym Min. Max Units VDD -GNDA -0.3 +6.0 V VEE -GNDA -6.0 +0.3 V +18.0 V VCC+ -GNDA 2 VCC- -GNDA -18.0 TSTG -55 Storage Temperature V +125 * Exceeding these values may cause damage. Functional operation under these conditions is not implied. Recommended Operating Conditions Parameters 1 2 Operating Supply Voltage Operating Current Sym Min. Typ‡ Max Units VDD 4.75 5.0 5.25 V VEE -5.25 -5.0 -4.75 V VCC+ 11.4 12.0 12.6 V VCC- -11.4 12.0 -12.6 V VBat -48 V IDD 7.0 mA IEE -7.0 mA ICC+ 8.0 mA ICC- -8.0 mA 265 mW 70 °C 3 Power Consumption PC 4 Operating Temperature TOP 0 Comments RINGND High ‡ Typical figures are at 25°C and are for design aid only: not guaranteed and not subject to production testing. 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 // 0.21µF) 6000Ω network 2-220 AGND Open (no connection) °C MH88630 Preliminary Information AC Electrical Characteristics† Characteristics Sym Min Typ‡ Max Units VR 40 90 130 Vrms 1 Ringing Voltage 2 Ringing Frequency 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 20 Ringing Type A, RS-464 70 mA RT 300 Ω @18mA RL 2300 Ω @18mA µA RINGND = 5.0Vdc mA -48VDC with 200Ω in series on Ring lead Ω with 10kΩ + 1.0µF inparallel 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 1000-3400Hz 3 100 IRG 600 longitudinal to metallic 10 18 Hz Test Conditions Return Loss Trunk to Line 11 Transhybrid Loss (single frequency) into 600Ω THL 16 18.5 34 30 dB dB dB 200Hz 1000Hz 3000Hz 12 Transhybrid Loss (single frequency) into AT&T Compromise THL 16 18 18 21 dB dB 200-1000Hz 1000-4000Hz 13 Frequency response (Output relative to 1kHz, VTR/VR and VX/VTR) 0.05 0.05 0.05 0.05 dB dB dB dB 200Hz 300Hz 3000Hz 3400Hz See Note 1 14 Idle Channel Noise 13 dBrncO C-Message 15 Power Supply rejection ratio 16 Analog signal overload level (adjustable gain) -0.15 -0.10 -0.10 -0.15 8 PSRR 40 dB 6 dBm 1kHz, 0dBm=0.775Vrms into 600Ω. † AC Electrical Characteristics are over recommended operating conditions unless otherwise stated. ‡ Typical figures are at 25°C and are for design aid only: not guaranteed and not subject to production testing. Note 1: Input 0dBm at VTR, or input 0.775Vrms at VR. TR-600Ω termination 2-221 MH88630 Preliminary Information DC Electrical Characteristics - Control Inputs 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 RC1, RC2 RINGND VIL RC1, RC2 RINGND IIL 3 4 Input Low Voltage Input Low Current Typ Max Units Test Conditions V V 5.0 -100 mA µA 0.7 V 1.0 1.1 µA mA Max Units DC Electrical Characteristics* Characteristics 1 2 3 4 Sym Min Typ Output High Voltage (TG, RC, RV, FC, RG) 4.75 V Output High Current (TG, RC, RV, FC, RG) 0.17 mA Output Low Voltage (TG, RC, RV, FC, RG) -0.3 V Output Low Sink Current (TG, RC, RV, FC, RG) -0.40 mA * DC Electrical Characteristics are over recommended operating conditions unless otherwise stated. 2-222 Test Conditions No Load on output VOH= -2.7Vdc No Load on output VOL= -0.4Vdc MH88630 Preliminary Information MH88630 C1 DUMMY RINGER VTR- 2 T TIP 11 27 TXIN+ LIGHTNING 31 R6 C2 RXIN+ PROTECTION C6 3 R RING 32 R1 K2A C3 RXIN- R2 33 K2B RXOUT AGND GSR -48V RETURN 6 XB 23 22 R3 K1A 13 LPGND -48V BATTERY 14 15 XC RGND 20 RC2 19 +12V K2 18 17 K1 16 TXIN- RD2 VTR+ CD K1B 26 C4 8 C5 10 R5 QB Q1 9 RD1 QE RC1 NETBAL 37 38 12 XA 30 7 RC RINGND RV VR FC VX 21 39 29 40 GSX RG 28 R4 36 TG VDD VEE 35 +5V 34 -5V VCC+ VCC24 25 +12V -12V Figure 3 - Application Circuit 2-223 MH88630 Preliminary Information 2 (50.8) 2 (50.8) 0.015 (0.381) Components 0.16 ± 0.05 (4.06 ± 1.27) AAAAAAAA AAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA 0.04 (1.02) 0.030 ± 0.015 (1.91 ± 0.381) Pin 1 AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA AAAAAAAA AAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAAAAAA AAAA 0.01 (2.54) 0.18 ± 0.015 (4.57 ± 0.381) Pin 2 Figure 4 - Physical Dimensions of 40 Pin Dual in Line Hybrid Package 2-224