MH88634K 데이터 시트보기 (PDF) - Mitel Networks

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MH88634K

Central Office Interface Circuit

Mitel Networks 

Preliminary Information

MH88634K

Pin Description (Continued)

Pin # Name

Description

17

VDD Positive Supply Voltage:. +5V

18

AGND Analog Ground: 4-wire ground. Connected to system ground.

19

LRC Loop Relay Control (Input): A logic high activates the Loop Relay Driver output (LRD). The

Loop Relay activates internal circuitry which provides a DC termination across Tip and Ring.

Used for line seizure and dial pulsing.

20

VRLY Relay Positive Supply Voltage: Typically +5V. Connects to the relay coil and the relay

supply voltage

21

LRD Loop Relay Drive (Output): Connects to the Loop Relay Coil. A logic low activates the

relay. An internal clamp diode from VRLY to LRD is provided.

Functional Description

The MH88634K is a COIC (Central Office Interface

Circuit) used to interface the Central Office 2-Wire

Analog Trunks. The COIC provides a Loop Start

interface function.

Incoming analog (voiceband) signals from the 2-Wire

circuit are applied differentially across Tip and Ring,

the output of which is applied to the 2 to 4 wire

converter with a fixed gain to the Tx output.

The outgoing analog signals are applied to Rx. The

audio signals undergo 4 to 2 wire conversion with a

fixed gain, and are differentially applied to Tip and

Ring.

DC Loop Termination

The line is provided with an active DC load

termination when a logic high is applied to the LRC

(Loop Start Relay) input. The termination is similar to

a DC resistance of less than 275 ohms. An external

relay is used to activate internal circuitry which

switches the termination in and out of the loop. This

is used for both seizing the line as well as generating

dial pulses.

Supervision Features

Forward loop and reverse loop detect - the FL output

provides a logic low when either forward loop battery

or forward loop current is detected (ring lead voltage

negative with respect to tip lead). The RL output

provides a logic low when either reverse loop battery

or reverse loop current is detected (tip lead voltage

negative with respect to ring lead).

Service Out detect - the SO output will detect the

loop current between 5mA to 10.13 mA as “out of

service” during the DC termination. The Central

Office applies -48V battery to the line but limits the

loop current to this range to indicate the line is out of

service. FL and RV outputs will not go low is the loop

current is less than 12.5mA.

Line Impedance

The input impedance of the MH88634K is 600 ohms.

The network balance is also set at 600 ohm to

maximize the Transhybrid Balance.

Transmit and Receive Gain

Transmit Gain (Tip-Ring) is set at 0dB and Receive

Gain (Rx to Tip-Ring) is set at -2dB.

The supervision circuitry provides the signalling

status outputs. The ringing voltage, forward current,

reverse current and Service Out. Ringing Voltage

detect - the RV output provides a logic low when

ringing voltage is detected. This sector includes a

ringing filter which ensures that the output toggles at

the ringing cadence and not at the ringing frequency.

Typically, this output goes low 50ms after the ringing

voltage is applied and remains low for 50ms after

ringing voltage is removed.

2-263

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