Advance Information
Functional Description
The Mitel MH88615 ONS SLIC provides a complete
interface between a switching system and a
subscriber loop. The functions provided by the
MH88615 include battery feed and integral ringing
amplifier feed to the subscriber line, 2W to 4W
conversion, constant current feed, off-hook and dial
pulse detection. The device is fabricated as a thick
film hybrid in a 20 pin single-in-line package.
The MH88615 is intended for applications where low
cost and basic functionality is important. The
MH88615 features an integral ringing amplifier which
enables a system designer to provide typically 60
Vrms ringing without having to generate a high
voltage, high current ac signal.
The SLIC uses a transformerless 2-4 wire converter
which can be connected to a CODEC to interface the
2 wire subscriber loop to a TDM (time division
multiplex) PCM (pulse code modulation) digital link.
Powering of the subscriber line is provided though
precision battery feed resistors on the hybrid. The
thick film hybrid circuit also contains control,
signalling and status circuits which combine to
provide a complete functional solution. A power
denial facility is provided which isolates the Battery
Feed from Tip and Ring.
The MH88615 is designed to meet German
regulatory approvals, UK regulatory approvals
(BS6305), and capable of meeting the approvals for
the USA (FCC Part 68/EIA 464).
MH88615
Power Denial
A logic high voltage applied to the power denial input
effectively removes the battery voltage from the loop
driver circuitry. The resulting loop current is
negligible and power consumption is minimised. The
power denial function is useful for disabling a loop
which may have a ground fault.
The SLIC is capable of detecting and indicating off-
hook and unbalanced conditions as well as inhibiting
ringing while in power denial.
Input and Network Impedance
The Input and Network Balance Impedances are
defined by the variant type on the MH88615.
MH88615-1Germany
Z
in
= 220Ω + (820Ω//115nF)
Z
net
= 220Ω +(820Ω//115nF)
MH88615-3 UK
Z
in
= 370Ω + (620Ω//310nF)
Z
net
= 300Ω + (1000Ω//220nF)
MH88615-7 North America
Z
in
= 600Ω
Z
net
= 350Ω (1kΩ//210nF)
Ringing Amplifier
The MH88615 incorporates an integral ringing
amplifier. A nominal 1.5Vrms ac signal is applied to
the RV pin and this produces a ringing signal of
typically 60 Vrms. This should ensure that the SLIC
can support a REN of 5.
Constant Current Feed
The loop current is programmed by the dc reference
voltage applied to V
Ref
.
Switch Hook Detection
When the dc current exceeds an internal threshold
level, the switch hook output (SHK) will go high. If
the loop resistance is so high that V
Bat
can no longer
supply the required loop current, the output SHK will
go low. This indicates that the loop resistance is too
high and the line is on hook.
Transmit Gain
Transmit gain (Tip-Ring to Vx) is fixed at 0.dB. A
dcbias on the ac input signal does not effect the
ringing signal.
Receive Gain
Receive Gain (VR to TIP-RING) is fixed at 0dB.
For correct gain, the SLIC input impedance must
match the line impedance
DC Loop Current Limit
Under Tip or Ring ground conditions the loop current
is nominally limited to 42mA.
2-141
MITEL [ MITEL NETWORKS CORPORATION ]
