Advance Information

MH88617

2-159

18

15

RV

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.

7

16

ESE

External Signal Enable. Meter pulse input enable.

8

17

ESI

External Signal Input. Meter pulse input.

2,

4,10

11,13

,23

25,24

18

IC

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

14

19

SHK

Switch Hook Detect (Output). A logic 1 at this pin indicates when the subscriber has

gone Off-Hook.

620

RC

Ringing Control (Input). A logic 1 will cause the ringing voltage to be applied to the line.

19

21

ZA

Line Impedance. Connect passive components from ZA to ground to match input and

line impedance.

Pin Description (continued)

28

Pin

DIL

21

Pin

SIL

Name

Description

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.

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

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.

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