Preliminary Information
Pin Description (continued)
18,
19
21,
22
24
25
27
28
NP
SC
VLOOP2
VLOOP1
RING
TIP
No Pin.
Isolation barrier, no pin fitted in this position.
MH88435-P
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.
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.
France’s current limit specification and Germany’s
dial pulse requirements are met by the MH88437.
This device is pin for pin compatible with the
MH88435.
Approval specifications are regularly changing and
the relevant specification should always be consulted
before commencing design.
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 and is classified as a Telecom
Network Voltage (TNV) circuit.
When Loop Control (LC) is at a logic 1, a line
termination is applied across Tip and Ring. The
device is 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 is approximately 300Ω
resistance, which is loop current dependent. It can
be programmed to meet different national
requirements. For normal operation Pin 22 and Pin
21 should be linked, and a resistor (R2) should be
fitted between VLOOP1 and VLOOP2 as shown in
Figure 5.
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 source for a given voltage across tip and
ring. Figure 3 shows how the voltage across tip and
ring varies with different resistors (R2) for a given
loop current.
The AC input impedance should be set by the user to
match the line impedance.
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 MH88435 has features such as programmable
input
and
network
balance
impedance,
programmable DC termination and a supplementary
isolation barrier that makes it ideal for use
throughout the world.
There are a small number of countries with a 100MΩ
leakage requirement that this device does not meet.
These are Belgium, Greece, Italy, Luxembourg and
Spain.
2-41
MITEL [ MITEL NETWORKS CORPORATION ]
