MH88510/11
The SHK output has low drive capability while the
LED output can drive an LED directly. The detection
circuit engages a ringing filter during applied ringing.
The ringing filter ensures that the SHK output toggles
at the ringing cadence and not at the ringing
frequency. The ring trip detection circuit also
prevents false off-hook detection due to the current
associated with the AC ringing voltage as well as
current transients when the ringing votlage is
switched in and out.
Preliminary Information
In addition, the Tip-Ring Drive Circuit has the
capability to drive a dry line (a line with no DC
current flowing); the AC Electrical Characteristics
apply (except for longitudinal balance), even when
the loop current drops to zero. Therefore, the
MH88510 has the capability to drive a line much
longer than 2000Ω providing the user is not
concerned with loop current, SHK detection or
ringing generator current.
Short Circuit Protection
Hybrid
The 2- wire hybrid circuit converts the incoming
balanced signal at Tip and Ring of the telephone line
into a ground referenced output signal at JUNC of
the SLIC, and converts the ground referenced input
signal at JUNC of the SLIC into a non-balanced
output signal at Tip and Ring of the telephone line.
The MH88510 is protected from long term (infinite)
short circuit conditions occurring between Tip and
Ring, Tip and AGND, and Ring and AGND.
Line Impedance
The MH88510’s Tip-Ring (Zin) impedance is fixed at
600Ω. For correct SLIC impedance, JUNC must be
appropriately terminated.
See AC Electrical
Characteristics.
Return Loss at Tip-Ring
To maximise return loss, the impedance at Tip-Ring
should match the SLIC’s impedance (600Ω).
However, the SLIC’s input impedance is dependent
on the JUNC termination resistance. For a 600Ω
SLIC input impedance, the JUNC must be
terminated with 754Ω.
Figure 2 illustrates a typical connection between two
SLICs through two crosspoint switches. Optimum
return loss occurs when JUNC is terminated with
754Ω. Since the JUNC input/output is 604Ω and the
crosspoint switches resistance are 75Ω + 75Ω, this
configuration gives optimum return loss as shown in
Figure 3.
Transmit and Receive Gain
Transmit Gain (JUNC to Tip-Ring) and Receive Gain
(Tip-Ring to JUNC) are fixed. For correct gain, the
SLIC input impedance must match the line
impedance and JUNC must be appropriately
terminated.
MUTE
A logic low at the MUTE input results on, muted
signals coming from Tip and Ring to the JUNC
terminal while allowing signals from the JUNC
terminal to Tip and Ring to be transmitted.
Tip-Ring Drive Circuit
The audio input ground referenced signal at JUNC is
converted to a differential output signal at Tip and
Ring. The output signal consists of the audio signal
superimposed on the DC battery feed current. The
Tip-Ring drive circuit is optimsed for good 2-Wire
longitudinal balance.
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MITEL [ MITEL NETWORKS CORPORATION ]
