MH88634CV-K
Pin Description (continued)
Pin #
16
Name
RL
Description
Data Sheet
Reverse Loop Detect (Output).
In the on-hook state, a logic 0 output indicates that reverse
loop battery is present. In the off-hook state, a logic 0 output indicates that reverse loop
current is present.
Positive Supply Voltage.
+5 V DC
Analog Ground.
4-wire ground (AGND). Normally connected to system ground.
Loop Relay Control (Input).
A logic 1 activates the Loop Relay Driver output (LRD).
Relay Positive Supply Voltage.
Typically +5 V. Connects to the relay supply voltage.
Loop Relay Drive (Output).
Connects to the Loop Relay Coil. When LRC is at a logic 1 an
open collector output at LRD sinks current and energizes the relay.
17
18
19
20
21
VCC
AGND
LRC
VRLY
LRD
Functional Description
The MH88634CV-K is a Central Office Interface Circuit (COIC). It is used to correctly terminate a Central Office 2-
wire telephone line. The device provides a signalling link and a 2-4 Wire line interface between the Telephone Line
and subscriber equipment. The subscriber equipment can include Private Branch Exchanges (PBXs), Key
Telephone Systems, Terminal Equipment, Digital Loop Carriers and Wireless Local Loops.
All descriptions assume that the device is connected as in the application circuit shown in Figure 3.
Isolation Barrier
The MH88634CV-K provides an isolation barrier which is designed to meet FCC Part 68 (November 1987) Leakage
Current Requirements.
External Protection Circuit
An external Protection Circuit Device assists in preventing damage to the device and the subscriber’s equipment,
due to over-voltage conditions. The type of protection required is dependant upon the application and regulatory
standards. Further details should be obtained from the specific country’s regulatory body. Typically you will need
lightening protection supplied by resettable fuses or PTC
TM
and mains crossover protection via a foldover diode.
Suitable Markets
The MH88634CV-K has fixed 600
Ω
line and network balance impedance for use in North America and Asia.
Line Termination
When LRC is at a logic 1, LRD will sink current which energizes the Loop Relay (K1), connecting XLA to XLB and
XLC to XLD. This places a line termination across Tip and Ring. The device can be considered to be in an off-hook
state and DC loop current will flow. The line termination consists of a DC resistance and an AC impedance. When
LRC is at a logic 0, the line termination is removed from across Tip and Ring.
An internal Dummy Ringer is permanently connected across Tip and Ring which is a series AC load of
(17kΩ+330nF). This represents a mechanical telephone ringer and allows ringing voltages to be sensed. This load
can be considered negligible when the line has been terminated.
Depending on the Network Protocol being used the Line Termination can terminate an incoming call, seize the line
for an outgoing call, or if applied and disconnected at the correct rate can be used to generate dial pulse signals.
3
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