Advance Information
Pin Description (continued)
28
Pin
DIL
18
21
Pin
SIL
15
Name
RV
Description
MH88617
Ringing Voltage.
A low level AC sinusoid is applied to this pin. This signal is amplified
and output from TIP/RING to the line as the ringing signal, when RC is at logic 1. This pin
should be driven with a low impedance AGND centred source.
External Signal Enable.
Meter pulse input enable.
External Signal Input.
Meter pulse input.
Internal Connection.
No connection should be made to this pin.
7
8
2,
4,10
11,13
,23
25,24
16
17
18
ESE
ESI
IC
14
6
19
19
20
21
SHK
RC
ZA
Switch Hook Detect (Output).
A logic 1 at this pin indicates when the subscriber has
gone Off-Hook.
Ringing Control (Input).
A logic 1 will cause the ringing voltage to be applied to the line.
Line Impedance.
Connect passive components from ZA to ground to match input and
line impedance.
device to the line and the signal from the line to the
device. The signal input at VR being sent to the line,
must not appear at the output VX. In order to prevent
this, the device has an internal cancellation circuit,
the measure of this attenuation is Transhybrid Loss
(THL).
The MH88617 has the ability to transmit analog
signals from VR through to Tip and Ring when on-
hook. This can be used when sending caller line
identification information.
Functional Description
The MH88617 is a Subscriber Line Interface Circuit
(SLIC) used to provide an analog interface between
the 4-wire connection and the 2-wire subscriber line
of a communications system.
It provides powering of the subscriber line along with
signalling, control and status circuits. This combines
to provide a comprehensive line and interface
solution in applications such as PABX, Key Systems,
Analog Terminal Adapters, Pair Gain Systems, Fibre
in the Loop and Wireless Local Loop.
Battery Feed and Loop Current Adjust
The MH88617 has an active feedback circuit to
regulate the DC current to the subscriber line. This
current is programmable over a wide range via the
LCA pin. With LCA open circuit the current will be set
to 24mA. This can be increased up to 55mA by
connecting a resistor between LCA and VCC or
reduced down to 14mA by connecting a resistor
between LCA and AGND. MSAN-156 shows a table
of resistor values and loop current.
The line driver stage is biased between +5V and
-48V DC. Therefore it should be noted that loop
current will flow in the +5V supply, this must be taken
into consideration when choosing the +5V supply.
The device will operate over a very wide VBAT
supply range but care must be taken when
programming the constant current that the maximum
power dissipation is not exceeded. For the majority
External Protection Circuit
An External Protection Circuit assists in preventing
damage to the device and the subscriber equipment,
due to over-voltage conditions (see Figure 3). Also
reference MSAN-156.
2-4 Wire Conversion
The SLIC converts the balanced 2-Wire input at Tip
and Ring to a ground referenced signal at VX. The
device converts the ground referenced signal input at
VR to a balanced 2-Wire signal across Tip and Ring.
Normally the VX and VR pins connect to a Codec
that interfaces the analog signal to a digital
network.During full duplex transmission, the signal at
Tip and Ring consists of both the signal from the
2-159
MITEL [ MITEL NETWORKS CORPORATION ]
