MH88634BV-4 데이터 시트보기 (PDF) - Mitel Networks

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MH88634BV-4

Central Office Interface Circuit

Mitel Networks 

Advance Information

MH88634B

Pin Description (continued)

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.

Functional Description

Line Termination

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 subscriber 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

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.

2-267

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