®
MH88634K
Central Office Interface Circuit
Preliminary Information
Features
•
•
•
Loop Start Trunk Interface
600 Ohm input impedance
Line state detection outputs:
- forward loop
- reverse loop
- ringing voltage
- service out
Transformerless 2W to 4W conversion
One loop start relay driver
+/- 5V operation
MH88634K
ISSUE 3
April 1995
Ordering Information
21 Pin SIL Package
0°C to 70°C
•
•
•
Description
The Mitel MH88634K Central Office Trunk Interface
circuit provides a complete audio and signalling link
between audio switching equipment and a central
office. The functions provided by the MH88634K
include 2-4 Wire conversion, 600 Ohm input
impedance and network balance. The device is
fabricated as a thick film hybrid incorporating various
technologies for optimum circuit design and very
high reliability.
Applications
Interface to Central Office for:
•
•
•
•
•
•
•
PABX
Key Telephone Systems
Channel Bank
Voice Mail
Terminal Equipment
Digital Loop Carrier
Optical Multiplexer
RING
TIP
VDD VEE AGND
RV
FL
RL
SO
Dummy
Ringer
Status
Detection
XLA
XLB
XLC
XLD
LRC
LRD
Loop
Termination
Receive
Gain
Rx
2 - 4 Wire Hybrid
Loop Relay
Driver
Impedance
Matching
Network
Balance
Transmit
Gain
Tx
VRLY
RGND
Figure 1 - Functional Block Diagram
2-261
MH88634K
Preliminary Information
TIP
RING
XLA
XLD
XLB
XLC
IC
IC
IC
SO
Rx
VEE
Tx
RV
FL
RL
VDD
AGND
LRC
VRLY
LRD
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Figure 2 - Pin Connections
Pin Description
Pin #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Name
TIP
RING
XLA
XLD
XLB
XLC
IC
IC
IC
SO
Rx
VEE
Tx
RV
Description
Tip Lead.
Connects to the “Tip” lead of the central office
Ring Lead:
Connects to the “Ring” lead of the central office
Loop Relay Contact A:.
Connects to XLB through the Loop relay (K1) contacts when the
relay is activated. This operates the internal active termination circuitry.
Loop Relay Contact D:
See XLC for description
Loop Relay Contact B:
See XLA for description
Loop Relay Contact C:
Connects to XLD through the loop relay (K1) contacts when the
relay is activated. This operates the internal active termination circuitry.
Internal Connection:
This pin is internally connected and must be left open.
Internal Connection.:
This pin is internally connected and must be left open.
Internal Connection:
This pin is internally connected and must be left open.
Service Out Detect (Output).
A logic low indicates that the central office “Tip” and “Ring”
are out of service.
Receive (Input):
4-Wire ground (AGND) referenced audio input.
Negative Supply Voltage.
-5V
Transmit (Output).
4-Wire ground (AGND) referenced audio output.
Ring Voltage Detect (Output).
A logic low indicates that ringing voltage is across the Tip
and Ring leads. Note that this output toggles at the ringing cadence and not at the ringing
frequency.
Forward Loop Detect (Output).
In the on-hook state, a logic low output indicates that
forward loop battery is present. In the off-hook state, a logic low indicates that forward loop
current is present
Reverse Loop Detect (Output):
In the on-hook state, a logic low output indicates that
reverse loop battery is present. In the off-hook state, a logic low output indicates that reverse
loop current is present. Reverse loop refers to the Tip lead negative respect to the Ring lead.
15
FL
16
RL
2-262
Preliminary Information
Pin Description (Continued)
Pin #
17
18
19
Name
VDD
AGND
LRC
Positive Supply Voltage:.
+5V
Analog Ground:
4-wire ground. Connected to system ground.
Description
MH88634K
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 MH88634K 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.
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).
Service Out detect - the SO output will detect the
loop current between 5mA to 10.13 mA as “out of
service” during the DC termination. The Central
Office applies -48V battery to the line but limits the
loop current to this range to indicate the line is out of
service. FL and RV outputs will not go low is the loop
current is less than 12.5mA.
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.
Line Impedance
The input impedance of the MH88634K is 600 ohms.
The network balance is also set at 600 ohm to
maximize the Transhybrid Balance.
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 signalling
status outputs. The ringing voltage, forward current,
reverse current and Service Out. 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
voltage is applied and remains low for 50ms after
ringing voltage is removed.
2-263
MH88634K
DC Electrical Characteristics
†
Characteristics
1
2
3
FL
RL
SO
RV
LRD
LRC
Supply Current
Power Consumption
Low Level Output Voltage
High Level Output Voltage
Sink Current, Relay to V
DD
Clamp Diode Current
Low Level Input Voltage
High Level Input Voltage
High Level Input Current
Low Level Input Current
Sym
I
DD
I
EE
PC
V
OL
V
OH
I
OL
I
CD
V
IL
V
IH
I
IH
I
IL
3.7
100
150
0.8
2.0
40
40
Min
0.5
0.5
Typ*
Max
13
13
137
0.5
Preliminary Information
Units
mA
mA
mW
V
V
mA
mA
V
V
µA
µA
Test Conditions
V
BAT
not connected
I
OL
= 4mA
I
OH
= 100µA
V
OL
= 0.35V not
continuous
4
5
6
V
IH
= 5.0V
* Typical figures are at 25°C with nominally +5V supplies and are for design use only.
† DC Electrical Characteristics are over recommended operating conditions unless otherwise stated.
Absolute Maximum Ratings*
Voltages are with respect to AGND
Parameters
1
DC Supply Voltages
Sym
V
BAT
V
DD
V
EE
V
VRLY
T
S
Min
0
-0.3
0.3
-0.3
-55
Max
-60
7
-7
7
+125
Units
V
V
V
V
°C
2
3
DC Ring Relay Voltage
Storage Temperature
* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
Recommended Operating Conditions
Parameters
1
2
3
DC Supply Voltages
DC Ring Relay Voltage
Operating Temperature
Symbol
V
DD
V
EE
V
VRLY
T
OP
0
Min
4.75
-4.75
Typ*
5.0
-5.0
5.0
Max
5.25
-5.25
15
70
Units
V
V
V
°C
Comments
* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
2-264
Preliminary Information
Loop Electrical Characteristics*
Characteristics
1
2
3
Ringing Voltage
Ringing Frequency
Ringer Equivalence number
REN
Symbol
VR
Min
40
16
0.5
Typ
†
90
20
1
Max
130
33
2
Units
V
rms
Hz
MH88634K
Test Conditions
Dummy Ringer is 17K
in series with 330nF.
Type A ringing
mA
Ω
Ω
mA
@ 20mA, -42.5V
@ 20mA
@ 1000Vac
50 or 60 Hz
LRC = 0v
LRC = 5V
LRC = 0v
LRC = 5V
V
BAT
= -48V
4
5
6
7
8
Operating Loop Current
Operating Loop Resistance
Off-Hook DC Resistance
Leakage Current
(Tip-Ring to AGND)
FL Threshold
Tip-Ring (On-hook)
Tip-ring Current (Off-Hook)
RL Threshold
Tip-Ring (On-Hook)
Tip-Ring current (Off-Hook)
SO Detect
15
0
250
70
1800
275
10
+30
12.5
-30
-12.5
-10.13
+40
15
-40
-15
-12.4
Vdc
mA
Vdc
mA
mA
9
10
* Loop Electrical Characteristics are over recommended operating conditions unless otherwise stated.
† Typical figures are at 25°C and are for design aid only.
AC Electrical Characteristics *
Characteristics
1
2
3
2-wire Input Impedance
Return Loss at 2-wire
(Z
in
= Ref = 600)
Longitudinal to Metallic
Balance
Transhybrid Loss
Gain (voltage) 2 wire to Tx
Gain (Voltage)
Rx to 2 wire
Input impedance at Rx
Output impedance at Tx
Signal Overload Level
at 2-wire output
at Tx
THD
1.0
1.0
NC
13
13
PSRR
30
30
dB
dB
dBrnc
dBrnc
Ripple 0.1V, 1kHz
%
%
Input 0.5V, 1kHz @ Rx
Input 0.5V, 1kHz @ Tip-Ring
4.0
0.95
THL
Sym
Z
in
RL
20
58
58
53
20
-0.25
-2.25
10
5
0
-2
0.25
-1.75
Min
Typ
†
600
Max
Units
Ω
dB
dB
200-3400 Hz
200Hz
1000Hz
3.4kHz
200-3400Hz
1024Hz
Spec Freq
Test Conditions
4
5
6
7
8
9
dB
dΒ
dB
kΩ
Ω
dBm
Vrms
% THD < 5%
Ref 600Ω @ 20mA
10 Total Harmonic Distortion
at 2-wire
at Tx
11 Idle Channel Noise
at 2-Wire
at Tx
12 Power Supply Rejection Ratio
at 2-wire and Tx
V
DD
V
EE
* AC Electrical Characteristics are over recommended operating conditions unless otherwise stated.
† Typical figures are at 25°C and are for design aid only.
2-265
京公网安备 11010802033920号
EEWORLD
