2-265

Features

Loop Start Trunk Interface

600

& 900

Input Impedance

2-4 Wire Conversion

Line state Detection Outputs:

- Forward Loop

- Reverse Loop

- Ringing Voltage

- Switch Hook

One Relay Driver

On-Hook Reception

Small footprint area

Meets FCC Part 68 Leakage Current
Requirements

Applications

Interface to Central Office for:
·

PABX

Key Telephone Systems

Channel Bank

Voice Mail

Terminal Equipment

Digital Loop Carrier

Optical Multiplexer

Description

The Mitel MH88634-2 Central Office Interface Circuit
trunk provides a complete analogue and signalling
link between audio switching equipment and a
telephone Line. The device is available in a single in
line package for high packing densities or with a lead
frame formed at 90

for low clearance applications.

The device is fabricated as a thick film hybrid
incorporating various technologies for optimum
circuit design and very high reliability.

This part supercedes the MH88634-2 and is pin for pin
compatible.

We advise that the B rev parts are fully tested.
However, we do not expect to see changes between
MH88634-2 and MH88634BV-2.

The component design has been changed to
improve the general performance of the part. It is
also now capable of operating at a 24V battery.

Figure 1 - Functional Block Diagram

Status

Detection

Receive

Gain

Transmit

Gain

2 - 4 Wire

Hybrid

Dummy

Ringer

Line

Termination

Loop Relay

Driver

Impedance

Matching

Network

Balance

XLA XLB XLC XLD

LRC

LRD

VRLY

RING

TIP

VCC

VEE

AGND

SHK

DS5061

ISSUE 6

January 1999

Ordering Information

MH88634BV-2

21 Pin SIL Package

MH88634BT-2

21 Pin 90

L/F Package

MH88634BV-4

21 Pin SIL Package

C to 70

MH88634B

Central Office Interface Circuit

Advance Information

MH88634B

Advance Information

2-266

Figure 2 - Pin Connections

Pin Description

Pin #

Name

Description

TIP

Tip Lead. Connects to the "Tip" lead of a Telephone Line.

RING

Ring Lead. Connects to the "Ring" lead of a Telephone Line.

XLA

Loop Relay Contact A. Connects to XLB through the Loop relay (K1) contacts when the
relay is activated.

XLD

Loop Relay Contact D. Connects to XLC through the loop relay (K1) contacts, when the
relay is activated.

XLB

Loop Relay Contact B. Connects to XLA through the loop relay (K1) contacts, when the
relay is activated.

XLC

Loop Relay Contact C. Connects to XLD through the loop relay (K1) contacts, when the
relay is activated.

7-9

Internal Connection. No connection should be made to this pin.

SHK

Switch Hook (Output). A logic 0 indicates the presence of forward or reverse battery
voltage when LRC is logic 0 and the presence of forward or reverse loop current when LRC
is logic 1.

Receive (Input). 4-Wire ground (AGND) referenced analog input.

VEE

Negative Supply Voltage. -5V DC

Transmit (Output). 4-Wire ground (AGND) referenced analog output.

Ringing Voltage Detect (Output). A logic low indicates that ringing voltage is across the Tip
and Ring leads.

Forward Loop Detect (Output). In the on-hook state, a logic 0 output indicates that
forward loop battery is present. In the off-hook state, a logic 0 indicates that forward loop
current is present.

Reverse Loop Detect (Output). In the on-hook state, a logic 0 output indicates that
reverse loop battery is present. In the off-hook state, a logic 0 output indicates that reverse
loop current is present.

VCC

Positive Supply Voltage. +5V DC

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

TIP

RING

XLA

XLB

XLC

IC
IC
IC

VEE

VCC

AGND

LRC

VRLY

LRD

XLD

SHK

21
20
19
18
17
16
15
14
13
12
11
10
9
8

6
5
4
3
2
1

Advance Information

MH88634B

2-267

AGND

Analog Ground. 4-wire ground (AGND). Normally connected to system ground.

LRC

Loop Relay Control (Input). A logic 1 activates the Loop Relay Driver output (LRD).

VRLY

Relay Positive Supply Voltage. Typically +5V. Connects to the relay supply voltage.

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.

Pin Description (continued)

Functional Description

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 PTC

and mains crossover

protection via a foldover diode.

Suitable Markets

The MH88634BV-2/BT-2 has fixed 600

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

Line Termination

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
(17k

+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 280

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 600

on the -2 variant and 900R on the -4.

MH88634B

Advance Information

2-268

Network Balance Impedance

The MH88634BV-2/BT-2's Network Balance
Impedance is fixed at 600

The MH88634BV-4 Network Balance Impedance is
fixed at 900R.

2-4 Wire Conversion

The device converts the balanced 2-Wire input,
presented by the line at Tip and Ring, to a ground
referenced signal at TX. This circuit operates with or
without loop current; signal reception with no loop
current is required for on-hook reception enabling the
detection of Caller Line Identification (CLI) signals.

Conversely the device converts the ground
referenced signal input at RX, to a balanced 2-Wire
signal across Tip and Ring.

The 4-Wire side (TX and RX) can be interfaced to a
filter/codec, such as the Mitel MT896X, for use in
digital voice switched systems

During full duplex transmission, the signal at Tip and
Ring consists of both the signal from the device to
the line and the signal from the line to the device.
The signal input at RX, being sent to the line, must
not appear at the output TX. In order to prevent this,
the device has an internal cancellation circuit. The
measure of attenuation is Transhybrid Loss (THL).

Transmit and Receive Gain

The Transmit Gain of the device is the gain from the
balanced signal across Tip and Ring to the ground
referenced signal at TX. It is set at 0dB.

The Receive Gain of the device is the gain from the
ground referenced signal at RX to the balanced
signal across Tip and Ring. It is set at -2dB.

Supervision Features

Line Status Detection Outputs

The MH88634 supervisory circuitry provides the
signalling status outputs which are monitored by the
system controller. The supervisory circuitry is
capable of detecting: Ringing Voltage; Forward and
Reverse loop battery; Forward and Reverse loop
current; and Switch Hook.

Ringing Voltage Detect Output (RV)

The RV output provides a logic 0 when ringing
voltage is detected across Tip and Ring. This
detector includes a filter which ensures that the
output toggles at the ringing cadence and not at the
ringing frequency. Typically this output switches to a
logic 0 after 50ms of applied ringing voltage and
remains at a logic 0 for 50ms after ringing voltage is
removed.

The threshold is different on the two variants. The
900R part has been designed to meet the ring
sensitivity requirements of TR57, 30 not detecting
ringin below 35Vrms.

Forward Loop and Reverse Loop Detect Outputs
(FL & RL)

The FL output provides a logic 0 when either forward
loop battery or forward loop current is detected, that
is the Ring pin voltage is more negative than the Tip
pin voltage.

The RL output provides a logic 0 when either reverse
loop battery or reverse loop current is detected, that
is the Tip pin voltage is more negative than the Ring
pin voltage.

Switch Hook (SHK)

The SHK output is active if either forward loop or
reverse loop current is detected, or if forward or
reverse battery voltage is detected.

Control Input

The MH88634 accepts a control signal from the
system controller at the Loop Relay Control input
(LRC). This energises the relay drive output Loop
Relay Drive (LRD). The output is active low and has
an internal clamp diode to VRLY.

The intended use of this relay driver is to add and
remove the Line Termination from across Tip and
Ring, as shown in Figure 3.

If this Control input and the Supervisory Features are
used as indicated in Figure 3, Loop-Start Signalling
can be implemented.

Mechanical Data

See Figure 9 for details of the mechanical
specification.

MH88634B

Advance Information

2-270

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

Typical figures are at 25

C with nominal 5V supplies and are for design aid only.

Electrical Characteristics are over recommended operating conditions unless otherwise stated.
Typical figures are at 25

C with nominal 5V supplies and are for design aid only.

Absolute Maximum Ratings*

Parameters

Sym

Min

Max

Units

Comments

DC Supply Voltages

-0.3

0.3

-7

V
V

DC Ring Relay Voltage

RLY

-0.3

Storage Temperature

-55

+125

°C

Ring Trip Current

TRIP

180

mArms

250ms 10% duty cycle or 500ms single shot

Recommended Operating Conditions

Parameters

Sym

Min

Typ

Max

Units

DC Supply Voltages

4.75

-4.75

5.0

-5.0

5.25

-5.25

V
V

DC Ring Relay Voltage

RLY

5.0

Operating Temperature

°C

DC Electrical Characteristics

Characteristics

Sym

Min

Typ

Max

Units

Test Conditions

Supply Current

2.5

13
13

mA
mA

Power Consumption

37.5

137

BAT

not connected

SHK

Low Level Output Voltage
High Level Output Voltage

2.4

0.5

V
V

= 4mA

= 0.4mA

LRD

Sink Current, Relay to
V

Clamp Diode Current

100
150

mA
mA

= 0.35V not

continuous, LRC=5V

LRC

Low Level Input Voltage
High Level Input Voltage

2.0

0.8

V
V

LRC

High Level Input Current
Low Level Input Current

40
40

= 5.0V

Advance Information

MH88634B

2-271

Electrical Characteristics are over recommended operating conditions unless otherwise stated.
Typical figures are at 25

C with nominal 5V supplies and are for design aid only.

Note 1: Maximum figure of 282

at 0

DC Electrical Characteristics

Characteristics

Symbol

Min

Typ

Max

Units

Test Conditions

Ringing Voltage

150

rms

-2 Variant only

17 to 68Hz

Detect
No Detect

106

rms

-4 Variant only
-4 Variant only

16-33Hz

(TR57 compliant)

Operating Loop Current

Off-Hook DC Resistance

270

280

@ 20mA Note 1

Leakage Current
(Tip-Ring to AGND)

mArms

@ 1000VAC

SHK & FL Threshold
Tip-Ring (On-hook)
Tip-Ring Current (Off-Hook)

21
15

Vdc

LRC = 0V
LRC = 5V

SHK & RL Threshold
Tip-Ring (On-Hook)
Tip-Ring Current (Off-Hook)

-5

-15

Vdc

LRC = 0V
LRC = 5V

MH88634B

Advance Information

2-272

Electrical Characteristics are over recommended operating conditions unless otherwise stated.
Typical figures are at 25

C with nominal 5V supplies and are for design aid only.

AC Electrical Characteristics

Characteristics

Symbol

Min

Typ

Max

Units

Test Conditions

2-wire Input Impedance

Zin

600
900

-2 Variant
-4 Variant

Return Loss at 2-wire

Test Circuit as Fig 6
200-3400 Hz

Longitudinal to Metallic
Balance

58
55
53

60
60
58

dB
dB
dB

Test Circuit as Fig 7
200Hz
1000Hz
3400Hz

Transhybrid Loss

THL

200-3400Hz

Gain, 2 wire to TX

Relative Gain

-0.25

-0.3

0
0

0.25

0.3

dB
dB

Test Circuit as Fig 4
1000Hz
200-3400Hz

Gain, Rx to 2 wire

Relative Gain

-2.25

-0.3

-2

-1.75

0.3

dB
dB

Test Circuit as Fig 5
1000Hz
200-3400Hz

Input impedance at RX

Output impedance at TX

Signal Overload Level
at 2-wire
at TX

4.0
1.7

dBm
dBm

% THD < 5% @ 20mA

Total Harmonic Distortion
at 2-wire

at TX

THD

1.0

Input 0.5V, 1kHz @
RX
Input 0.5V, 1kHz @
Tip-Ring

Idle Channel Noise
at 2-Wire
at TX

15
15

16.5
16.5

dBrnC
dBrnC

Power Supply Rejection Ratio
at 2-wire and TX
V

PSRR

25
25

48
47

dB
dB

Ripple 0.1V, 1kHz

On-Hook Gain, 2-Wire to TX
Relative to Off-Hook Gain

-1

Input 1000Hz @ 0.5V

Met. to Long. Balance

-2 Variant

-4 Variant

60
40
55
40

62
48
62
48

Test Circuit as Fig. 8

200-1000Hz
1000-3400Hz
200-1000Hz
1000-3400Hz

Common Mode Rejection
Ratio

CMRR

Test Circuit as Fig. 7
1000Hz, FL = 0V,
I

Loop

= 25mA

Advance Information

MH88634B

2-275

Figure 8 - Metallic to Longitudinal Balance Test Circuit

Figure 9 - Mechanical Data

368

Met to Long Bal. = 20 * Log (V1\Vs)

100uF

-V

RING

TIP

XLA

XLB

XLC

XLD

Vs = 0.5V

AGND

VCC

VEE

100uF

+5V

-5V

I = 25mA

10H 300

368

510

0.625 Max

(15.9 Max)

0.020 +0.005

(0.5 +0.13)

0.100 + 0.010

(6.35+0.51)

0.250+0.020

0.180 + 0.020

(4.57 + 0.51)

(2.54 + 0.25)

0.14 Max

(3.6 Max)

0.010 + 0.002

(0.25 + 0.05)

0.13 Max

(3.3 Max)

Notes:

1) Not to scale
2) Dimensions in inches. (Dimensions in millimetres)

* Dimensions to centre of pin.

3) Pin tolerances are non-accumulative.
4) Recommended soldering conditions: Wave soldering tempetature 260°C for 10 secs.

2.120 Max

(53.85 Max)

TECHNICAL DOCUMENTATION - NOT FOR RESALE

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Tel: +1 (613) 592 2122

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Europe, Middle East,

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Tel: +65 333 6193

and Africa (EMEA)

Fax: +1 (770) 631 8213

Fax: +65 333 6192

Tel: +44 (0) 1793 518528

Fax: +44 (0) 1793 518581

http://www.mitelsemi.com

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liability for errors that may appear in this publication, or for liability otherwise arising from the application or use of any such information, product or service or for any infringement of
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data used is up to date and has not been superseded. Manufacturing does not necessarily include testing of all functions or parameters. These products are not suitable for use in
any medical products whose failure to perform may result in significant injury or death to the user. All products and materials are sold and services provided subject to Mitel's
conditions of sale which are available on request.

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