MITEL MH88422-1, MH88422S-1, MH88422S-2, MH88422S-3, MH88422-3 Datasheet

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

Features

• FAX and Modem interf ace (V 29/V2 2 bis)

• Variants mat ch Germ an, UK & 600

Ω network

impedance s

• Provides reinforced barrier to interna tional PTT requiremen ts

• Transformerless 2-4 W ire conversion

• Loop star t oper ation

• Pulse and DT MF ope rati on

• Accommo date s extern al mo nitor ph one

• Line state detec tion out put s:

• -loo p curr ent/ri nging outp uts

• Single +5V operat ion, l ow idle po wer (5 mW)

• Full Duplex

• Suitable for p ower dow n ap plica tions

Applications

Interface to Central Office for:

•DAA

• Modem

•FAX

• Answering M achi ne

• Terminal Equip men t

Description

The Mitel MH88422 Line Interface Circuit provides a complete audio and signalling link between audio equipment and central office. The functions provided by the MH88422 include 2-4 Wire conversion, loop seizure, ring voltage and loop current detection. The device is fabricated as thick film hybrid which incorporates various technologies for optimum circuit design, high voltage isolation and very high reliability.

Variants are provided to meet German (-1) and UK (-3) line impedance (see section on Line Impedances), as well as a 600Ω variants (-2).

ISSUE 5 April 1995

Ordering Information

MH88422 -1 14 Pin DIL Pac kage MH88422 -2 14 Pin DIL Packag e MH88422 -3 14 Pin DIL Packag e

Surface Mount Options are available by adding the

Suffix “S”

Power

Supply

Opto-

Isolation

Logic Inp ut

Buffer

Opto-

Isolation

Opto-

Isolation

Opto-

Isolation

Audio

Buffer

Audio Buffer

Ring &

Loop

Buffer

Transhybrid

Loss

Cancellat io n

Circuit

Active

Termina tio n

Audio Input

Buffer

Input Buffer

Isolation Barrier

VDD AGND

RVLC

TIP

RING

TXIN

RLS

USER CONNECTIONS

NETWORK CONNECTIONS

Figure 1 - Functional Block Diagram

MH88422

Line Interface Circuit

Preliminary Information

2-22

MH88422 Preliminary Information

Figure 2 - Pin Connections

Pin Description

Pin # Name Description

1VDDPositive Pow er Su pp ly Voltage. +5V. 2AGNDAnalog Ground. 4-Wire Ground. Normally connect ed to System Ground. 3LC

Loop Control (Input). A logic low activates internal circuitr y which provides a dc termination across Tip and Ring. Used for seizing the line and dial pulsing.

4RVLCRin g Voltage and Current Detect (Output). A logic low indicates that loop current is

detected. The loop current can be due to the external monitor phone or the MH88422 in the off-hook mode. The RVLC output pulses when the external monitor phone is dial pulsing or when the MH88422 is dial pulsing via the LC

input. In addition, when the MH88422 is on the on-hook mode, a pulsing output indicates ringing voltage across the Tip and Ring leads. The pulsing output frequency is twice the ringing frequency.

5NCNo Connection sho uld be mad e to this pin. 6VXTransmit (Outp ut ). 4-Wire ground (AGND) referenced audio out put , biased at 2.5V.

Outputs in off-h ook mode only.

7VRRecei ve (In pu t). 4-Wire ground (AG ND) referenced audio input , biased at 2.5V. LC

must be activated low and loop current must be flowing .

8NCNo Connection sho uld be mad e to this pin. 9 RING Ring Lead. Connects to the “Ring” lead of the central office through an opt iona l relay

contact. The central office “Tip” and “Ring” leads may be interchanged.

10 TXIN Transmit (Input). Connects to the “Ring” lead of the central offi ce through a coupli ng

capacitor.

11 TF Tip Feed. Connects to the “Tip” lead of the central office through an internal resistor and

an optional external resistor.

12 NC No Connection sho uld be made to thi s pin. 13 RLS Ring Loop Sense (Input). Sense node for ringing voltage detector and the loop current

detector.

14 TIP Tip Lead. Connects to the “Tip” lead of the central office through an optional relay

contact. The central office “Tip” and “Ring” leads may be interchanged.

RLS NC TF TXIN

TIP

AGND

RING

RVLC

VDD

1 2 3 4 5

6 78

Preliminary Information MH88422

2-23

Functional Description

The MH88422 Line Interface Circuit is a COIC (Central Office Interface Circuit) used to interface FAX’s Modems or user defined equipment to Central Office 2-Wire Analog Trunks.

Opto-Isolation

The isolation barrier is designed to meet regulatory requirements for a reinforced barrier of 3kVac. It provides full isolation of mains voltages up to 250V RMS and all telecom voltages.

In order that this barrier is not bypassed a creepage/ clearance distance of 6.4mm minimum must be maintained between wiring, pcb tracking, etc., connected to external circuitry on either side of the barrier. To make this requirement simpler, pins on the MH88422 connected to opposite sides of the barrier are on opposite sides of the package.

External Protection Circuit

To meet regulatory high voltage requirement, an external protection circuit is required. The protection circuit shown in Figure 3 (Clamp Diode D1) is recommended.

DC Loop Termination

The DC loop termination circuitry provides the loop with an active DC load termination when a logic low is applied to the LC

(Loop Control) input. The termination is similar to a resistance of approximately 300Ω (loop current dependent). Internal optically isolated circuitry is used to switch the termination in and out the loop. This is used for both seizing the line as well as generating dial pulses. The MH88422 will not seize the line when powered down.

Supervision Features

The supervision circuitry is capable of detecting ringing voltage and loop current as well as the status of an optional external monitor phone. The RVLC (Ring Voltage Loop Current Detect) output provides a logic low when loop current flows due to the external monitor phone or the MH88422 being in the off-hook mo de .

The RVLC outputs pulses when the external monitor phone is dial pulsing or when the MH88422 is dial pulsing via the LC

mode.

In addition, when the MH88422 is on-hook, a pulsing output indicates that ringing voltage is across the tip and ring leads; the pulsing output frequency is twice the ringing frequency. See Figure 3.

Ringing frequency may require external validation. An RC monostable is usually satisfactory for this purpose or this may also be achieved using software applications.

2-4 Wire Conversion

The 2-4 Wire conversion circuit converts the balanced full duplex signal at Tip and Ring of the central office line into a transmit ground referenced signal at VX (Transmit) of the MH88422. It also converts the receive ground referenced signal at VR (Receive) of the MH88422 into a balanced transmit signal at Tip and Ring of the central office line.

In full duplex transmission, the Tip-Ring signal consists of an audio signal from the central office as well as an audio signal due to the VR input. There is an internal cancellation circuit which prevents the V

signal appearing at the VX output. The degree to which the 2-4 wire conver sion circuit min imizes the contribution of the VR signal at the VX output is specified as transhybrid loss (THL).

The MH88422 is suitable to drive a COMBO II codec or a VLSI modem device.

Line Impedance

The MH88422 provides a fixed Tip-ring impedance which conforms to the following PTT requirements.

MH88422-1 Zin = 200 + 820 // 115nF

Germany

MH88422-2 Zin = 600Ω

MH88422-3 Zin = 370 + 620 // 310nF

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MH88422 Preliminary Information

* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied

‡ Typical figures are at 25°C with nom inal +5V suppl y and are for design aid only

Loop Electrical Characteristics*

* Loop Electrical Characteristics are over recommended operating conditions unless otherwise stated. ‡ Typical figures are at 25°C and are for desi gn aid only. Note 1: All of the above characteristics use a test circuit as per Figure 3.

Absolute Maximum Ratings* - All voltages are with respect to AGND unless otherwise specified.

Parameter Symbol Min Max Units

1 DC Supply Voltage V

-0.3 6 V

2 Storage Temperature T

-55 +80 °C

3 DC Loop Voltage V

Bat

-100 +100 V

4 Ringing Voltage V

- 120 V

RMS

5 Loop Current I

Loop

-90

Recommended Operating Conditions.

Parameters Sym Min Typ

‡

Max Units Test Conditions

1 DC Supply Voltages V

4.5 5.0 5.5 V

2 Operating Temperature T

070°C

3 Ringing Voltage V

75 V

RMS

Bat

=-48V

Characteristics Sym Min Typ

‡

Max Units Test Conditions

Ringing Voltage No Detect

-1 Variant only Detect

20 V

RMS

Refer to FT2 1TR2 for test method

Ringing Voltage No Detect All other Variants Detect

RMS

Externally Adjustable

Ringing Frequency 15 68 Hz

On-Hook 2-wire Impedance 40k Ω 1kHz

Operating Loop Current 15 80 mA

Operating Loop Resista nce 2800 Ω V

Bat

=-48V, I

Loop

=15mA

Off-Hook DC -1 Variant Voltage

-2 Variant

-3 Variant

6.0

4.0

6.0

9.6 15

6.0

7.8

9.0

12.5

V V V V V V

Loop

=25mA

Loop

=42mA

Loop

=15-20mA

Loop

=26mA

Loop

=25mA

Loop

=42mA

Leakage Current (2-Wire to AGND) 10 µA 100V

Leakage Current on Hook (Tip to Ring)

910µAV

Bat

=-50V

DC Resistance during dialling

-1 variant only 200 220 Ω I

Loop

=20-40mA

Dial Pulse Distort ion ON

-1 Variant OFF All other Variant

+2 +8 +2

+10

ms ms ms

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