MITEL MH88634K Datasheet

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MH88634K

Central Office Interface Circuit

Preliminary Info rm atio n

Features

• Loop Star t Trunk Inter face

• 600 Ohm input impedance

• Line s tate de tect ion ou tputs:

- forward loop

- reverse loop

- ringing voltag e

- service out

• Transformerless 2W to 4W conversion

• One loop sta rt relay driver

• +/- 5V operation

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 3 April 1995

Ordering Information

MH88634 K 21 Pin SIL Pac kage

0°C to 70°C

Description

The Mitel MH88634K C entral Office Trunk In terface circuit provides a complete audio and signalling link between audio switching equipment and a central office. The functions provided by the MH88634K 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

Ring er

Loop

Termination

2 - 4 Wire Hybrid

Loop Relay

Driver

Impedance

Matching

VRLY RGND

Network Balance

Figure 1 - Functional Blo ck Diag ram

FL RL SOVDD VEE AGND

Status

Detection

Receive

Gain

Transmit

Gain

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MH88634K Preliminary Information

TIP

RING

XLA

XLD

XLB XLC

IC IC IC

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 # Name Description

1TIPTip Lead. Connects to the “Tip” lead of the central office 2RINGRing Lead: Connects to the “Ring” lea d of the central office 3XLALoop Relay Contact A:. Connects to XLB throu gh the Loop relay (K1) contacts when the

relay is activated. This operates the int ernal 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 operates the int ernal 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 SO

Service Out Detect (Output). A logic low indicates that the central offi ce “Tip” and “Ring”

are out of service.

11 Rx Receive (Input ): 4-Wire ground (AGND) referenced audio input. 12 VEE Negative Supply V o ltage. -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 indicate s that

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

current is present

16 RL

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Reverse Loop Detect (Output): In the on-hook state, a logic low output indicate s that

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

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

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

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

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

supply voltage

21 LRD

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

is provided.

Functional Description

Forward loop and reverse loop detect - the FL

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.

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).

Service Out detect - the SO 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.

output will detect the

). The

output

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 terminat ion 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 signalling status outputs. The ringing voltage, forward current, reverse current and Service Out. 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 voltage is applied and remains low for 50ms after ringing voltage is removed.

output provides a logic low when

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.

Tr a nsmit and Rec eiv e Ga in

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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