Advance Information
Pin Description (continued)
Pin #
20,23
26
21,22
24
25
27
28
Name
IC
SC
VLOOP2
VLOOP1
RING
TIP
Description
MH88437-P
Internal Connection.
No connection should be made to this pin externally.
Short Circuit.
These two pins should be connected to each other via a 0Ω link.
Loop Voltage Control Node 2.
Used to set DC termination characteristics.
Loop Voltage Control Node 1.
Used to set DC termination characteristics.
Ring Lead.
Connects to the “Ring” lead of the telephone line.
Tip Lead.
Connects to the “Tip” lead of the telephone line.
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.
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.
Line Termination
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.
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 300Ω
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.
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 100MΩ 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
Network Balance
The network balance impedance of the device can
be programmed by adding external components By
3
MITEL [ MITEL NETWORKS CORPORATION ]
