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Zarlink Semiconductor Inc.
Zarlink, ZL and the Zarlink Semiconductor logo are trademarks of Zarlink Semiconductor Inc.
Copyright 2003, 2001 Zarlink Semiconductor Inc. All Rights Reserved.
Features
Loop Start Trunk Interface
600
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 Zarlink MH88634CV-K Central Office Interface
Circuit trunk provides a complete analog and signalling
link between audio switching equipment and a
telephone line.
The device is fabricated as a thick film hybrid
incorporating various technologies for optimum circuit
design and very high reliability.
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 and on hook
reception.
The main difference between the MH88634BV-2 and
MH88634CV-K is that SHK is active high on the CV-K.
September 2003
Ordering Information
MH88634CV-K 21 Pin SIL Package
0
C to 70C
MH88634CV-K
Central Office Interface Circuit
Data Sheet
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
RV
VCC
RX
TX
VEE
AGND
FL
RL
SHK
MH88634CV-K
Data Sheet
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Zarlink Semiconductor Inc.
Figure 2 - Pin Connections
Pin Description
Pin #
Name
Description
1
TIP
Tip Lead. Connects to the "Tip" lead of a Telephone Line.
2
RING
Ring Lead. Connects to the "Ring" lead of a Telephone Line.
3
XLA
Loop Relay Contact A. Connects to XLB through the Loop relay (K1) contacts when the
relay is activated.
4
XLD
Loop Relay Contact D. Connects to XLC through the loop relay (K1) contacts, when the
relay is activated.
5
XLB
Loop Relay Contact B. Connects to XLA through the loop relay (K1) contacts, when the
relay is activated.
6
XLC
Loop Relay Contact C. Connects to XLD through the loop relay (K1) contacts, when the
relay is activated.
7-9
IC
Internal Connection. No connection should be made to this pin.
10
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.
11
RX
Receive (Input). 4-Wire ground (AGND) referenced analog input.
12
VEE
Negative Supply Voltage. -5V DC
13
TX
Transmit (Output). 4-Wire ground (AGND) referenced analog output.
14
RV
Ringing Voltage Detect (Output). A logic low indicates that ringing voltage is across the Tip
and Ring leads.
15
FL
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.
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
RX
VEE
TX
RV
FL
RL
VCC
AGND
LRC
VRLY
LRD
21
XLD
SHK
MH88634CV-K
Data Sheet
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Zarlink Semiconductor Inc.
Functional Description
The MH88634CV-K 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 MH88634CV-K 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 regulatory
standards. Further details should be obtained from the specific country's regulatory body. Typically you will need
lightening protection supplied by resettable fuses or PTC
TM
and mains crossover protection via a foldover diode.
Suitable Markets
The MH88634CV-K has fixed 600
line and network balance impedance for use in North America and Asia.
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.
16
RL
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.
17
VCC
Positive Supply Voltage. +5V DC
18
AGND
Analog Ground. 4-wire ground (AGND). Normally connected to system ground.
19
LRC
Loop Relay Control (Input). A logic 1 activates the Loop Relay Driver output (LRD).
20
VRLY
Relay Positive Supply Voltage. Typically +5V. Connects to the relay supply voltage.
21
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)
Pin #
Name
Description
MH88634CV-K
Data Sheet
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Zarlink Semiconductor Inc.
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 MH88634CV-K places across Tip and Ring to terminate
the Telephone line. This is fixed at 600
.
Network Balance Impedance
The MH88634CV-K Network Balance Impedance is fixed at 600
.
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 Zarlink 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 MH88634CV-K 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
MH88634CV-K
Data Sheet
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Zarlink Semiconductor Inc.
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.
RV shall not toggle during ringing.
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 MH88634CV-K accepts a control signal from the system controller at the Loop Relay Control input (LRC). This
energizes 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.
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