Advance Information

MH88437-P

3

20,23

26

IC

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

21,22

SC

Short Circuit. These two pins should be connected to each other via a 0

Ω link.

24

VLOOP2

Loop Voltage Control Node 2. Used to set DC termination characteristics.

25

VLOOP1

Loop Voltage Control Node 1. Used to set DC termination characteristics.

27

RING

Ring Lead. Connects to the “Ring” lead of the telephone line.

28

TIP

Tip Lead. Connects to the “Tip” lead of the telephone line.

Pin Description (continued)

Pin #

Name

Description

Functional Description

The device is a Data Access Arrangement (D.A.A.). It

is used to correctly terminate a 2-Wire telephone

line. It provides a signalling link and a 2-4 Wire line

interface between an analog loop and subscriber

data transmission equipment, such as Modems,

Facsimiles (Fax’s), Remote Meters, Electronic Point

of Sale equipment and Set Top Boxes.

Isolation Barrier

The device provides an isolation barrier capable of

meeting the supplementary barrier requirements of

the international standard IEC 950 and the national

variants of this scheme such as EN 60950 for

European applications and UL 1950 for North

American applications.

External Protection Circuit

An External Protection Circuit assists in preventing

damage to the device and the subscriber equipment,

due to over-voltage conditions. See Application Note

MSAN-154 for recommendations.

Suitable Markets

The MH88437 has features such as programmable

line and network balance impedance, programmable

DC

termination

and

a

supplementary

isolation

barrier. For countries that do not need to meet the

French and German requirements there is a pin for

pin compatible device the MH88435.

There are, however, a small number of countries with

a 100M

Ω leakage requirement that this device does

not

meet.

These

are

Belgium,

Greece,

Italy,

Luxembourg,

Spain

and

Poland.

Although

Luxembourg will now accept TBR21 and there are

exceptions to the Italian specification, in most

applications

the

MH88437

will

comply

with

Luxembourg and Italian specifications. For approval

in Denmark and Sweden the TRB21 route is

recommended.

Approval specifications are regularly changing and

the relevant specification should always be consulted

before commencing design.

Line Termination

When Loop Control (LC) is at a logic 1, a line

termination is applied across Tip and Ring. The

device can be considered off-hook and DC loop

current will flow. The line termination consists of both

a DC line termination and an AC input impedance. It

is used to terminate an incoming call, seize the line

for an outgoing call, or if it is applied and

disconnected at the required rate, can be used to

generate dial pulses.

The DC termination resembles approximately 300

Ω

resistance,

which

is

loop

current

dependent.

Furthermore, it can be programmed to meet different

national

requirements.

For

normal

operation

VLOOP3 should be open circuit and a resistor (R2)

should be fitted between VLOOP1 and VLOOP2, as

shown in Figure 4.

The approval specification will give a DC mask

characteristic that the equipment will need to comply

to. The DC mask specifies the amount of current the

DAA can sink for a given voltage across tip and ring.

Graph 1 shows how the voltage across tip and ring

varies with different resistors (R2) for a given loop

current.

Network Balance

The network balance impedance of the device can

be programmed by adding external components By