MITEL MH88634-2 Datasheet

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MH88634

Central Office Interface Circuit

Preliminary Info rm atio n

Features

• Loop Star t Trunk Inter face

• 600 ohm input impedance, -2 variant

• Line state detection outputs: forward loop, reverse loop, ringing voltage, switch hook On-hook recept ion

• Transformerless 2W to 4W conversion

• One loop sta rt relay driver

• +/- 5V operation

• Small footprint area (<4.75cm

)

Applications

Interface to Central Office for:

• PABX

• Key Telephone S ystem s

• Channel B a nk

•Voice Mail

• Terminal Equipm ent

• Digital Loop Carrier

• Optical Multiplexer

ISSUE 2 April 1995

Ordering Information

MH88634-2 21 Pin SIL Package

0°C to 70°C

Description

The Mitel MH88634 Central Office Trunk Interface circuit provides a complete audio and signalling link between audio switching equipment and a central office. The functions provided by the MH88634 include 2-4 Wire conversion, 600 ohm input impedance and network balance. The device is fabricated as a thick film hybrid incorporating various technologies for optimum circuit design and very high reliability.

XLA XLB XLC XLD

LRC LRD

RING TIP RV

Dummy

Ringer

Loop

Termination

2-4 Wire Hybrid

Loop Relay

Driver

Impedance

Matching

VRLY RGND

Network Balance

Figure 1 - Functional Blo ck Diag ram

FL RL SHKVDD VEE AGND

Status

Detectio n

Receive

Gain

Transmit

Gain

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MH88634 Preliminary Information

TIP

RING

XLA

XLD

XLB XLC

IC IC IC

SHK

VEE

FL RL

VDD

AGND

LRC

VRLY

LRD

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Figure 2 - Pin Connections

Pin Description

Pin #

1TIPTip Lead: Connects to the “Tip” lead of the central office

Name Description

2RINGRing Lead: Connects to the “Ring” lead of the central office 3XLALoop Relay Contact A:. Connects to XLB through the Loop relay (K1) contacts when the

relay is activated. This operate s the internal active termi nati on cir cuitry. 4XLDLoop Relay Con tact D: See XLC for description 5XLBLoop Relay Contact B: See XLA for description 6XLCLoop Relay Con tact C: Connects to XLD through the loop relay (K1) contacts when the

relay is activated. This operate s the internal active termi nati on cir cuitry. 7ICInternal Connection: This pin is internally connected and must be left open. 8ICInternal Connection.: This pin is internally connected and must be left open. 9ICInternal Connection: This pin is internally connected and must be left open.

10 SHK

Switch Hook (Outpu t). A logic low indicates either forward or reverse loop current.

11 Rx Receive (Input ): 4-Wire ground (AGND) referenced audio input. 12 VEE Negative Sup ply Voltage. -5V 13 Tx Transmit (Output). 4-Wire ground (AGND) referenced audio output. 14 RV

Ring Voltage Detect (Output ). A logic low indicates that ringing volt age is across the Tip

and Ring leads. Note that this output toggles at the ringing cadence and not at the ringing

frequency.

15 FL

Forward Loop Detect (Output): In the on-hook state, a logic low output indicates that

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

current is present.

16 RL

Reverse Loop Detect (Output). In the on-hook state, a logic low outpu t indicates that

reverse loop battery is present. In the off-hook state, a logic low output indicates th at

reverse loop current is present. Reverse loop refers to the Tip lead negative respect to the

Ring Lead.

17 VDD Positive Supply V o ltage: +5V

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Preliminary Information MH88634

Pin Description (Continued)

Pin #

18 AGND An a lo g G round. 4-wire ground. Connected to system ground 19 LRC Loop Relay Control (Input): A logic high activates the Loop Relay Driver output (LRD

20 VRLY Relay Positive S up pl y Voltage. Typically +5V. Connects to the relay coil and the relay

21 LRD

Functional Description

The MH88634 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

Name Des cription

The Loop Relay activates internal circuitry which provides a DC termination across Tip and Ring. Used for line seizure and dial pulsing.

supply voltage Loop Relay Dri ve (Outp ut). Connects to the Loop Relay coil. A logic low activates the

relay. An internal clamp diode from VRLY to LRD

voltage is applied and remains low for 50ms after ringing voltage is removed.

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 provides a logic low when either reverse loop battery or reverse loop current is detected (tip lead voltage negative with respect to ring lead)

SHK

output is active if either forward loop or reverse

loop current is detected.

is provided.

Line Impedance

The input impedance of the MH88634-2 is 600 ohms. The network balance is also set at 600 ohms to maximize the Transhybrid Balance.

output

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

The supervision circuitry provides, the signally status outputs. The ringing voltage, forward current, reverse current and switch hook. Ringing Voltage detect - the RV 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

output provides a logic low when

Transmit an d Rec eiv e G ain

Transmit Gain (Tip-Ring) is set at 0dB and Receive Gain (Rx to Tip-Rin g ) is se t at -2 d B.

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