MITEL MT88634BV-2, MT88634BT-2, MT88634BV-4 Datasheet

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Features

• Loop Start Trunk Interface

• 600Ω & 900Ω Input Impedance

• 2-4 Wire Conversion

• Line state Detection Outputs:

• - Forward Loop

• - Reverse Loop

• - Ringing Voltage

• - Switch Hook

• One Relay Driver

• On-Hook Reception

• Small footprint area

• Meets FCC Part 68 Leakage Current Requirements

Applications

Interface to Central Ofﬁce for:

• PABX

• Key Telephone Systems

• Channel Bank

• Voice Mail

• Ter minal Equipment

• Digital Loop Carrier

• Optical Multiplexer

Description

The Mitel MH88634-2 Central Ofﬁce Interface Circuit trunk provides a complete analogue and signalling link between audio switching equipment and a telephone Line. The device is available in a single in line package for high packing densities or with a lead frame formed at 90° for low clearance applications.

The device is fabricated as a thick ﬁlm hybrid incorporating various technologies for optimum circuit design and very high reliability.

This part supercedes the MH88634-2 and is pin for pin compatible.

We advise that the B rev parts are fully tested. However, we do not expect to see changes between MH88634-2 and MH88634BV-2.

The component design has been changed to improve the general performance of the part. It is also now capable of operating at a 24V battery.

Figure 1 - Functional Block Diagram

Status

Detection

Receive

Gain

Transmit

Gain

2 - 4 Wire

Hybrid

Dummy

Ringer

Line

Termination

Loop Relay

Driver

Impedance

Matching

Network Balance

XLA XLB XLC

XLD

LRC LRD

VRLY

RING

TIP

VCC

VEE AGND

FL RL

SHK

DS5061 ISSUE 6 January 1999

Ordering Information

MH88634BV-2 21 Pin SIL Package

MH88634BT-2 21 Pin 90° L/F Package MH88634BV-4 21 Pin SIL Package

0°C to 70°C

MH88634B

Central Ofﬁce Interface Circuit

Advance Information

MH88634B Advance Information

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Figure 2 - Pin Connections

Pin Description

Pin # Name Description

1 TIP Tip Lead. Connects to the "Tip" lead of a Telephone Line. 2 RING Ring Lead. Connects to the "Ring" lead of a Telephone Line. 3 XLA Loop Relay Contact A. Connects to XLB through the Loop relay (K1) contacts when the

relay is activated.

4 XLD Loop Relay Contact D. Connects to XLC through the loop relay (K1) contacts, when the

relay is activated.

5 XLB Loop Relay Contact B. Connects to XLA through the loop relay (K1) contacts, when the

relay is activated.

6 XLC Loop Relay Contact C. Connects to XLD through the loop relay (K1) contacts, when the

relay is activated.

7-9 IC Internal Connection. No connection should be made to this pin.

10 SHK Switch Hook (Output). A logic 0 indicates the presence of forward or reverse battery

voltage when LRC is logic 0 and the presence of forward or reverse loop current when LRC

is logic 1. 11 RX Receive (Input). 4-Wire ground (AGND) referenced analog input. 12 VEE Negative Supply Voltage. -5V DC 13 TX Transmit (Output). 4-Wire ground (AGND) referenced analog output. 14 RV Ringing Voltage Detect (Output). A logic low indicates that ringing voltage is across the Tip

and Ring leads. 15 FL Forward Loop Detect (Output). In the on-hook state, a logic 0 output indicates that

forward loop battery is present. In the off-hook state, a logic 0 indicates that forward loop

current is present. 16 RL Reverse Loop Detect (Output). In the on-hook state, a logic 0 output indicates that

reverse loop battery is present. In the off-hook state, a logic 0 output indicates that reverse

loop current is present. 17 VCC Positive Supply Voltage. +5V DC

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

TIP

RING

XLA

XLB

XLC

IC IC IC

VEE

VCC

AGND

LRC

VRLY

LRD

XLD

SHK

21 20 19 18 17 16 15 14 13 12 11 10 9 8

6 5 4 3 2 1

Advance Information MH88634B

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18 AGND Analog Ground. 4-wire ground (AGND). Normally connected to system ground. 19 LRC Loop Relay Control (Input). A logic 1 activates the Loop Relay Driver output (LRD). 20 VRLY Relay Positive Supply Voltage. Typically +5V. Connects to the relay supply voltage. 21 LRD Loop Relay Drive (Output). Connects to the Loop Relay Coil. When LRC is at a logic 1 an

open collector output at LRD sinks current and energizes the relay.

Pin Description (continued)

Functional Description

The MH88634 is a Central Ofﬁce Interface Circuit (COIC). It is used to correctly terminate a Central Ofﬁce 2-wire telephone line. The device provides a signalling link and a 2-4 Wire line interface between the Telephone Line and subscr iber equipment. The subscriber equipment can include Private Branch Exchanges (PBXs), Key Telephone Systems, Terminal Equipment, Digital Loop Carriers and Wireless Local Loops.

All descriptions assume that the device is connected as in the application circuit shown in Figure 3.

Isolation Barrier

The MH88634 provides an isolation barrier which is designed to meet FCC Part 68 (November 1987) Leakage Current Requirements.

External Protection Circuit

An external Protection Circuit Device assists in preventing damage to the device and the subscriber’s equipment, due to over-voltage conditions. The type of protection required is dependant upon the application and regulatorary standards. Further details should be obtained from the speciﬁc country’s regulatorary body. Typically you will need lightening protection supplied by resettable fuses or PTCTM and mains crossover protection via a foldover diode.

Suitable Markets

The MH88634BV-2/BT-2 has ﬁxed 600Ω line and network balance impedance for use in North America and Asia.

The MH88634BV-4 has a ﬁxed 900R impedance and is also suitable for some applications in North and South America

Line Termination

When LRC is at a logic 1, LRD will sink current which energizes the Loop Relay (K1), connecting XLA to XLB and XLC to XLD. This places a line termination across Tip and Ring. The device can be considered to be in an off-hook state and DC loop current will ﬂow. The line termination consists of a DC resistance and an AC impedance. When LRC is at a logic 0, the line termination is removed from across Tip and Ring.

An internal Dummy Ringer is permanently connected across Tip and Ring which is a series AC load of (17kΩ+330nF). This represents a mechanical telephone ringer and allows ringing voltages to be sensed. This load can be considered negligible when the line has been terminated.

Depending on the Network Protocol being used the Line Termination can terminate an incoming call, seize the line for an outgoing call, or if applied and disconnected at the correct rate can be used to generate dial pulse signals.

The DC line termination circuitry provides the line with an active DC load termination which is equivalent to a DC resistance of 280Ω at 20mA

Ringing Equivalent Number

The Ringing Equivalent Number (REN) is application speciﬁc. See the governing regulatory body speciﬁcation for details.

Input Impedance

The input impedance (Zin) is the AC impedance that the MH88634 places across Tip and Ring to terminate the Telephone line. This is ﬁxed at 600Ω on the -2 variant and 900R on the -4.

MH88634B Advance Information

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Network Balance Impedance

The MH88634BV-2/BT-2’s Network Balance Impedance is ﬁxed at 600Ω.

The MH88634BV-4 Network Balance Impedance is ﬁxed at 900R.

2-4 Wire Conversion

The device converts the balanced 2-Wire input, presented by the line at Tip and Ring, to a ground referenced signal at TX. This circuit operates with or without loop current; signal reception with no loop current is required for on-hook reception enabling the detection of Caller Line Identiﬁcation (CLI) signals.

Conversely the device converts the ground referenced signal input at RX, to a balanced 2-Wire signal across Tip and Ring.

The 4-Wire side (TX and RX) can be interfaced to a ﬁlter/codec, such as the Mitel MT896X, for use in digital voice switched systems

During full duplex transmission, the signal at Tip and Ring consists of both the signal from the device to the line and the signal from the line to the device. The signal input at RX, being sent to the line, must not appear at the output TX. In order to prevent this, the device has an internal cancellation circuit. The measure of attenuation is Transhybrid Loss (THL).

Transmit and Receive Gain

The Transmit Gain of the device is the gain from the balanced signal across Tip and Ring to the ground referenced signal at TX. It is set at 0dB.

The Receive Gain of the device is the gain from the ground referenced signal at RX to the balanced signal across Tip and Ring. It is set at -2dB.

Supervision Features

Line Status Detection Outputs

The MH88634 supervisory circuitry provides the signalling status outputs which are monitored by the system controller. The supervisory circuitry is capable of detecting: Ringing Voltage; Forward and Reverse loop battery; Forward and Reverse loop current; and Switch Hook.

Ringing Voltage Detect Output (RV) The RV output provides a logic 0 when ringing

voltage is detected across Tip and Ring. This detector includes a ﬁlter which ensures that the output toggles at the ringing cadence and not at the ringing frequency. Typically this output switches to a logic 0 after 50ms of applied ringing voltage and remains at a logic 0 for 50ms after ringing voltage is removed.

The threshold is different on the two variants. The 900R part has been designed to meet the ring sensitivity requirements of TR57, 30 not detecting ringin below 35Vrms.

Forward Loop and Reverse Loop Detect Outputs (FL & RL)

The FL output provides a logic 0 when either forward loop battery or forward loop current is detected, that is the Ring pin voltage is more negative than the Tip pin voltage.

The RL output provides a logic 0 when either reverse loop battery or reverse loop current is detected, that is the Tip pin voltage is more negative than the Ring pin voltage.

Switch Hook (SHK) The SHK output is active if either forward loop or

reverse loop current is detected, or if forward or reverse battery voltage is detected.

Control Input

The MH88634 accepts a control signal from the system controller at the Loop Relay Control input (LRC). This energises the relay drive output Loop Relay Drive (LRD). The output is active low and has an internal clamp diode to VRLY.

The intended use of this relay driver is to add and remove the Line Termination from across Tip and Ring, as shown in Figure 3.

If this Control input and the Supervisory Features are used as indicated in Figure 3, Loop-Start Signalling can be implemented.

Mechanical Data

See Figure 9 for details of the mechanical speciﬁcation.

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