MH88614 데이터 시트보기 (PDF) - Mitel Networks
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MH88614 Datasheet PDF : 10 Pages
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MH88614
Advance Information
The hybrid also provides an output which is
proportional to the loop length / resistance. LA must
be high for ILoop to be valid.
RLoop = - [(10 x VLoop)-1.5]
ILoop
- 82Ω
Where VLoop = the voltage at Loop
ILoop = the programmed line current
Constant Current Control
Whilst working within the RLoop maximum limit set by
the ILoop & VBat levels chosen the circuit allows the loop
current to be set to one of the two discrete levels by
the use of the loop current adjust pin. Applying a logic
low to this pin sets the constant current to the lowest
level. By changing the level to a logic high the constant
current is set to the highest level. This feature can be
used with the loop alarm signal when setting up the
line to chose the loop current setting most suitable.
Line Drivers & Battery Feed
The Line Drivers & Battery Feed circuit provide
power to the line and allow bi-directional audio
transmission.
The line impedance present by the line driver
circuitry is a nominal 600 ohms, allowing the circuit
to be used on its own in a PABX application. The
nominal impedance can be modified to look like a
complex impedance such as those used within
Europe by allowing an impedance to be reflected
through the SLIC from the CODEC or DSP module.
The outputs at tip & ring protected from short term
over voltage between tip & gnd, ring to gnd or tip to
ring reducing the requirement for secondary
protection circuitry.
There is also long term protection on the outputs
against short circuits applied across tip & ring, tip to
gnd, ring to gnd and tip & ring to gnd.
Switch circuits
There are three switches built into the functionality of
this circuit, they are Ringing Enable, Message Signal
Enable and Power Denial.
Ringing Enable allows a logic level to be applied to a
pin and the ringing voltage superimposed on a d.c.
level to then be switched onto the line. The ringing
signal applied to the line at zero voltage crossing and
switched off at zero current. (see figure 3). The
ringing signal can be terminated by either returning
the Ringing Enable pin to a logic low level or it will
automatically stop when the phone goes off hook
regardless of the state of the input pin.
The Message Signal Enable pin provides the
switching control of the message voltage. A logic
high on the MSE pin applies the message voltage to
the line. Internal circuitry allows the input signal to
MSE to be cadenced, causing the output signal to be
cadenced, without causing bell tinkle. This is
possible by conditioning the rising and falling edges
of the output signal. Message Signal Enable also has
auto trip facility.
RE
IRING
SHK
1
0
tt
tt
30/45mA
Off Hook
ILOOP
0mA
On Hook
Figure 3 - Call Supervision
2-132
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