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MH88630
Central Office Interface (LS/GS) Preliminary Information
Features
* * Transformerless 2-4 Wire conversion Line state detection outputs: * * * forward current reverse current ring ground tip ground ringing voltage
ISSUE 7
April 1995
Ordering Information MH88630 40-Pin DIL Package 0C to 70C
Description
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.
Programmable audio transmit and receive gain Loop start or ground start termination Selectable 600 or AT&T compromise balance network
Applications
* * * * PBX Interface to Central Office Channel bank Intercom Key system
RG FC
RV RC TG
LPGND RINGND
VCC+ VCC- AGND
T R
Signal Detection Circuitry
Ring Ground
Relay Driver 1 Relay Driver 2
VTR+ VTRRXINRXIN+
Network Balance Active Termination Audio Section Circuitry (2 - 4 Wire)
RC1 RD1 RGND CD RD2 RC2 NETBAL GSX VX VR GSR
QB QE XA XB
XC
VDD
VEE
RXOUT
TXIN+
TXIN-
Figure 1 - Functional Block Diagram
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MH88630
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
Preliminary Information
Figure 2 - Pin Connections
Pin Description
Pin # 1 2 3 4 5 6 7 Name IC T R IC IC LPGND RINGND Description Internal Connection. Pin cut short. Leave open circuit. Tip (Input). Normally connects to the "Tip" lead of the C.O. Ring (Input). Normally connects to the "Ring" lead of the C.O. Internal Connection. Leave open circuit. Internal Connection. Leave open circuit. Loop Ground is the system ground reference with respect to -48 volts. 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 (390). This is a signal to the C.O. that the interface is seizing the line. Connects to the collector of an external transistor (Q1) and TXIN - (pin 26) via an external capacitor. Connects to the emitter of an external transistor (Q1). Connects to the base of an external transistor (Q1). Connects to the TXIN+ (pin 27), via an external capacitor (C1). External relay contact (K1) connection from VTR+ (pin 8), activated by loop seize control input (RC1). External relay contact (K1) connection from XC (pin 14), activated by loop seize control input (RC1). External relay contact (K1) connection from XB (pin 13), activated by loop seize control input (RC1). Relay Ground. Relay Control 1 (Input). A logic high will activate the relay (K1) to provide loop seize across Tip and Ring. Relay Driver 1 (Output): Open collector sinks current when RC1 is high. Diode clamp protected. Clamping Diode: Normally connects to the positive supply voltage.
8 9 10 11 12 13 14 15 16 17 18
VTR+ QE QB VTRXA XB XC RGND RC1 RD1 CD
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Preliminary Information
Pin Description (Continued)
Pin # 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Name RD2 RC2 VR GSR RXOUT VCC+ VCCTXINTXIN+ GSX VX NETBAL RXIN+ RXINAGND VEE VDD TG RC RV FC RG Description
MH88630
Relay Driver 2 (Output): Open collector sinks current when RC2 is high. Diode clamp protected. 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. 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). Positive analog Power Supply Voltage (+12V). Negative analog Power Supply Voltage (-12V). Transmit (Input). Different audio signal from VTR+ (pin 8), via an external capacitor (C4). Transmit (Input). Different audio signal from VTR- (pin 11), via an external decoupling capacitor (C1). Gain Setting Transmit (Input). Normally used to set the transmit gain with an external resistor connected to VX (pin 29). Audio Transmit (Output). The 4-wire audio signal output from the interface. Network Balance (Input). When there is no connection (open), the network is balanced at 600. When this pin is grounded, the network is balanced at AT&T compromise. Differential Receive (Input). Connects to analog ground via an external capacitor (C2). Differential Receive (Input). Connects to RXOUT (pin 23) via an external capacitor (C3). Analog Ground. Negative Power Supply (-5V). Positive Power Supply (+5V). Tip Lead Ground Detect (Output). Active low. Reverse Loop current Detect (Output). Active low. Ringing Voltage Detect (Output). Active low. Forward Loop Current Detect (Output). Active low Ring Lead Ground Detect (Output). Active low.
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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 600 balance, used when feeding channel banks or when performing external
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 600. If the NETBAL input pin is grounded, the interface is balanced against the AT&T compromise network consisting of 350 plus 1k shunted by a 0.21F 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
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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. External Circuitry Requirements 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 500 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. 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
MH88630
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 600 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. Components List (for Figure 3) R1*, R2 = 30.9k, 1%, 1/4 W = Receive Gain Adjust Resistor = 523.2 E3 x Gain VTR/VR Typical Value = 505k, 1%, 1/4 W R3 = Transmit Gain Adjust Resistor = 301.5 E3 x Gain VX/VTR-100 E3 Typical Value = 200k, 1%, 1/4 W R5 = 510, 5%, 1/4 W R6 = 10k, 5%, 1/4 W C1, C2, C3, C4 = 0.22F, 10%, 200V C5 = 0.1F, 5%, 250V C6 = 1.0F, 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.
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MH88630
Absolute Maximum Ratings* - Voltages are with respect to AGND.
Parameters 1 DC Supply Voltages
Preliminary Information
Sym VDD -GNDA VEE -GNDA VCC+ -GNDA VCC- -GNDA
Min. -0.3 -6.0
Max +6.0 +0.3 +18.0
Units V V V V
-18.0 -55 +125
2
Storage Temperature
TSTG
C
* Exceeding these values may cause damage. Functional operation under these conditions is not implied.
Recommended Operating Conditions
Parameters 1 Operating Supply Voltage Sym VDD VEE VCC+ VCC2 Operating Current VBat IDD IEE ICC+ ICC3 4 Power Consumption Operating Temperature PC TOP 0 Min. 4.75 -5.25 11.4 -11.4 Typ 5.0 -5.0 12.0 12.0 -48 7.0 -7.0 8.0 -8.0 265 70 Max 5.25 -4.75 12.6 -12.6 Units V V V V V mA mA mA mA mW C RINGND High Comments
Typical figures are at 25C and are for design aid only: not guaranteed and not subject to production testing.
Control Inputs State Table
Parameter 1 2 3 4 RC1 RC2 RINGND NETBAL AT&T compromise network (350 + 1k // 0.21F) 6000 network Active Logic High Logic High Logic Low Idle Logic Low Logic Low Logic High
AGND Open (no connection)
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Preliminary Information
AC Electrical Characteristics
Characteristics 1 2 3 4 5 6 7 8 Ringing Voltage Ringing Frequency Operating Loop Current Off-Hook DC Resistance Operating Loop Resistance On-Hook Leakage Current Ring Ground Sink Current Tip and Ring AC Impedance
IRG IL RT RL
MH88630
Sym
VR
Min 40
Typ 90 20
Max 130
Units Vrms Hz
Test Conditions
Ringing Type A, RS-464
18
70 300 2300 3 100 600
mA A mA @18mA @18mA RINGND = 5.0Vdc -48VDC with 200 in series on Ring lead with 10k + 1.0F inparallel with Tip and Ring 200-1000Hz 1000-4000Hz 200-1020Hz 1020-3020Hz 200-500Hz 500-1000Hz 1000-3400Hz 200Hz 1000Hz 3000Hz 200-1000Hz 1000-4000Hz 200Hz 300Hz 3000Hz 3400Hz See Note 1 C-Message
9
Longitudinal Balance metallic to longitudinal longitudinal to metallic
60 40 58 53 20 26 30 THL 16 18.5 34 30 18 21 0.05 0.05 0.05 0.05 8 PSRR 40 6 13
dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB
dBrncO
10
Return Loss Trunk to Line
11
Transhybrid Loss (single frequency) into 600 Transhybrid Loss (single frequency) into AT&T Compromise Frequency response (Output relative to 1kHz, VTR/VR and VX/VTR)
12
THL
16 18 -0.15 -0.10 -0.10 -0.15
13
14 15 16
Idle Channel Noise Power Supply rejection ratio Analog signal overload level (adjustable gain)
dB dBm 1kHz, 0dBm=0.775Vrms into 600.
AC Electrical Characteristics are over recommended operating conditions unless otherwise stated. Typical figures are at 25C 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-600 termination
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MH88630
DC Electrical Characteristics - Control Inputs
Characteristics 1 2 3 4 Input High Voltage Input High Current Input Low Voltage Input Low Current RC1, RC2 RINGND RC1, RC2 RINGND RC1, RC2 RINGND RC1, RC2 RINGND Sym VIH IIH VIL 0.7 IIL 1.0 1.1 Min 2.7 4.5 2.5
5.0
Preliminary Information
Typ
Max
Units V V
Test Conditions
-100
mA A V A mA
DC Electrical Characteristics*
Characteristics 1 2 3 4 Output High Voltage (TG, RC, RV, FC, RG) Output High Current (TG, RC, RV, FC, RG) Output Low Voltage (TG, RC, RV, FC, RG) Output Low Sink Current (TG, RC, RV, FC, RG) Sym Min Typ 4.75 0.17 -0.3 -0.40 Max Units V mA V mA Test Conditions No Load on output VOH= -2.7Vdc No Load on output VOL= -0.4Vdc
* DC Electrical Characteristics are over recommended operating conditions unless otherwise stated.
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Preliminary Information
MH88630
MH88630
C1 DUMMY RINGER 2 VTRT TXIN+ R6 RXIN+ C6 3 R 32 C3 RXIN33 RXOUT AGND GSR XB LPGND 15 RGND 20 RC2 19 12 XA TXINVTR+ CD RD1 QB 9 QE 30 7 RINGND 21 VR 29 FC 40 RG 36 TG VDD VEE 35 34 VCC+ VCC24 25 VX GSX 28 R4 Q1 26 8 10 R5 K1B C4 C5 14 XC 23 22 13 R3 K1A 31 C2 11 27
TIP LIGHTNING PROTECTION RING R1 K2A R2 K2B
-48V RETURN 6 -48V BATTERY
+12V
K2 18 17 K1 16 37
RD2
RC1
NETBAL
RC 38 39 RV
+5V
-5V
+12V -12V
Figure 3 - Application Circuit
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MH88630
Preliminary Information
2 (50.8)
2 (50.8)
0.015 (0.381)
Components
0.16 0.05 (4.06 1.27) 0.04 (1.02)
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0.030 0.015 (1.91 0.381)
0.01 (2.54) 0.18 0.015 (4.57 0.381)
Pin 1 Pin 2
Figure 4 - Physical Dimensions of 40 Pin Dual in Line Hybrid Package
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