Preliminary Information
Pin Description (Continued)
Pin #
18
19
Name
AGND
LRC
Description
Analog Ground.
4-wire ground. Connected to system ground
MH88634
Loop Relay Control (Input):
A logic high activates the Loop Relay Driver output (LRD).
The Loop Relay activates internal circuitry which provides a DC termination across Tip and
Ring. Used for line seizure and dial pulsing.
Relay Positive Supply Voltage.
Typically +5V. Connects to the relay coil and the relay
supply voltage
Loop Relay Drive (Output).
Connects to the Loop Relay coil. A logic low activates the
relay. An internal clamp diode from VRLY to LRD is provided.
20
21
VRLY
LRD
Functional Description
The MH88634 is a COIC (Central Office Interface
Circuit) used to interface the Central Office 2-Wire
analog trunks. The COIC provides a Loop Start
interface function.
Incoming analog (voiceband) signals from the 2-Wire
circuit are applied differentially across Tip and Ring
the output of which is applied to the 2 to 4 wire
converter with a fixed gain to the Tx output.
The outgoing analog signals are applied to Rx. The
audio signals undergo 4 to 2 wire conversion with a
fixed gain, and are differentially applied to Tip and
Ring.
voltage is applied and remains low for 50ms after
ringing voltage is removed.
Forward loop and reverse loop detect - the FL output
provides a logic low when either forward loop battery
or forward loop current is detected (ring lead voltage
negative with respect to tip lead). The RL output
provides a logic low when either reverse loop battery
or reverse loop current is detected (tip lead voltage
negative with respect to ring lead)
SHK output is active if either forward loop or reverse
loop current is detected.
Line Impedance
The input impedance of the MH88634-2 is 600 ohms.
The network balance is also set at 600 ohms to
maximize the Transhybrid Balance.
DC Loop Termination
The line is provided with an active DC load
termination when a logic high is applied to the LRC
(Loop Start Relay) input. The termination is similar to
a DC resistance of less than 275 ohms. An external
relay is used to activate internal circuitry which
switches the termination in and out of the loop. This
is used for both seizing the line as well as generating
dial pulses.
Transmit and Receive Gain
Transmit Gain (Tip-Ring) is set at 0dB and Receive
Gain (Rx to Tip-Ring) is set at -2dB.
Supervision Features
The supervision circuitry provides, the signally status
outputs. The ringing voltage, forward current,
reverse current and switch hook. Ringing Voltage
detect - the RV output provides a logic low when
ringing voltage is detected. This sector includes a
ringing filter which ensures that the output toggles at
the ringing cadence and not at the ringing frequency.
Typically, this output goes low 50ms after the ringing
2-255
MITEL [ MITEL NETWORKS CORPORATION ]
