MH88500
®
Hybrid Subscriber Line Interface Circuit (SLIC)
Preliminary Information
Features
•
•
•
•
•
•
•
•
•
•
Differential to single ended conversion
No transformers required
Minimum installation space
Off-Hook detection and LED indicator drive
Relay drive output
Battery and ringing feed to line
Logic interface: MUTE, OFHK, RC
Mute of incoming audio
Dial pulse detection
Voltage surge protection
MH88500
ISSUE 5
April 1995
Ordering Information
20 Pin SIL Package
0°C to 70°C
Description
The Mitel MH88500 Subscriber Line Interface Circuit
provides a complete interface between the telephone
line and a speech switch requiring only single
bidirectional switch per crosspoint. The functions
provided by the MH88500 include bidirectional
differential to single ended conversion in the speech
path, line battery feed, ringing feed and loop and dial
pulse detection. The device is fabricated as a thick
film hybrid in a 20-pin ‘single-in-line’ package
allowing optimum circuit board packing density.
Applications
Line Interface for:
• PABX
•
•
Intercoms
Key Systems
VA
1
V
A2
V
B
V
C1
GND
TIP
RING
RING
FEED
Loop Feed/
Ring Feed
Speech Circuit
JUNCTOR
V
A2
CD
V
B
MUTE
OFHK
RD
RC
RGND
Loop Detection
Relay Drive
Circuit
LED
THRESH ADJ
V
C2
Figure 1 - Functional Block Diagram
2-33
MH88500
TIP
VA1
RING
RING FEED
IC
VC1
GND
V
B
LED
OFHK
THRESH ADJ
VA2
GND
VC2
MUTE
JUNCTOR
RD
RGND
RC
CD
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Preliminary Information
Figure 2 - Pin Connections
Pin Description
Pin #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Name
TIP
V
A1
RING
RING FEED
IC
V
C1
GND
V
B
LED
OFHK
THRESH ADJ
V
A2
GND
V
C2
MUTE
JUNCTOR
RD
RGND
RC
CD
Description
Tip Lead.
Connects to the “Tip” lead (A-wire) of the telephone line.
Positive Line Feed Supply Voltage.
Normally connected to V
A2
.
Ring Lead.
Connects to the “Ring” lead (B-wire) of the telephone line.
Negative Line Feed Voltage and Ringing Input.
Normally connected to Ring Relay.
Internal Connection.
Leave open circuit. Use for testing only.
Sense Input.
Normally connected to negative line feed voltage supply.
Analog ground (0V).
Internally connected to pin 13.
Negative Analog Supply Voltage.
LED Drive Output.
Drives an LED directly. Off-Hook condition, logic low.
Logic Low Output.
Indicates closed loop condition (Off-Hook and dial pulsing).
Allows adjustment of OFHK detection threshold.
Positive Power Supply
Voltage. Normally connected to V
A1
.
Analog Ground (0V).
Internally connected to pin 7.
Loop Detector Voltage Supply.Connected
to negative line feed voltages supply.
Input mutes the incoming audio. Active low.
Receive/transmit audio speech path.
(referenced to 0V GND)
Relay Drive Output.
Open collector sinks current when RC high. Diode clamp
protected.
Ground for Relay Drive Circuit.
Ring Control Input.
Active high.
Clamping Diode.
Normally connected to relay positive voltage.
2-34
Preliminary Information
Functional Description
Speech Circuit
The speech circuit converts the bidirectional TIP and
RING line pair to a bidirectional single ended junctor
line. Figure 3 illustrates a typical connection between
two SLIC’s through two crosspoint switches. This
configuration gives optimum transhybrid loss as
seen from Figure 4 given that the output impedance
of the Junctor line is 604Ω.
The MUTE input mutes signals coming from TIP and
RING to the junctor line while allowing the signal
from the junctor to the tip-ring pair to be transmitted.
MH88500
Line Feed/Ring Feed Circuit
The line feed circuit provides loop current and the
ability to apply ringing onto TIP and RING. The
impedance from Ring Feed to GND is 600Ω which
gives the loop current as:
IL = Voltage at RING FEED pin
Telephone Impedance + 600
Amps
The positive supply for the line feed circuit is V
A1
through the loop current is determined from RING
FEED and GND.
Relay Drive Circuit
The relay drive circuit switches ringing onto RING
FEED (Fig.7). The diode is present to suppress
voltage transients during relay switches caused by
the inductive coils of the relay. Ringing voltage
includes AC ringing (90V typically) an dDC line
feed voltage (-24V typically).
Loop Detection
The loop detection circuit determines whether a low
enough impedances is across TIP and RING to be
recognized as an off-hook condition.
(Threshold impedance = 5.4kΩ with no adjustment)
This threshold level can be adjusted by the use of
external resistors as shown in Figure 6. OFHK has
low output drive capability so it may drive CMOS
operating with different power supplies.
MH88500
1
TIP
TIP
JUNC
RING
3
RING
CROSSPOINT
SWITCH
16
75Ω
MH88500
1
TIP
TIP
JUNC
RING
3
RING
CROSSPOINT
SWITCH
16
75Ω
Figure 3 - SLIC Crosspoint Switch Connection
2-35
MH88500
Absolute Maximum Ratings
†
Parameter
1
Voltage Supplies - V
Ref
to GND
Symbol
V
A1,
V
A2
V
B
V
C1
, V
C2
2
3
4
5
Clamp Diode Breakdown Voltage-V
Ref
to RGND
Operating Temperature
Storage Temperature
Power Dissipation
V
CD
T
AMB
T
STG
P
D
Preliminary Information
Min
Max
Units
V
-18
-35
+18
V
V
+15
0
-40
+70
+100
1.2
V
°C
°C
Watt
† Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
AC Electrical Characteristics
†
Voltages are with respect to ground (V
SS
), TA = 25°C, unless otherwise stated.
Test conditions unless noted, V
A1
=V
A2
=+7V, V
B
=8V, V
C2
=-24V(+5%).
Characteristics
1
Junctor to differential output (tip-
ring) gain.
Differential Input (tip-ring) to junctor
gain
On/Off Hook Detection
Threshold
Loop Resist
Loop Current
4
5
6
7
8
Trans Hybrid Loss
Passband Linearity
Power Supply Rejection Ratio
(VC to Junctor)
Common Mode Rejection Ratio
(Tip and Ring to Junctor)
Low Frequency Cutoff (3dB)
Junctor to Line
Line to Junctor
High Frequency Cutoff (3dB)
Line to Junctor
Junctor to Line
Longitudinal Balance
Tip (or Ring) to ground AC input
impedance
Junctor output impedance
Sym
A
JL
Min
2.18
Typ
‡
2.25
7
0.321
Max
2.32
Units
V/V
dB
V/V
dB
Test Conditions
1kHz, 400mV
RMS
source on pin 16.
Note 2
1kHz, 1V
RMS
Source on pins 1&3.
Note 1,2
2
A
LJ
0.303
0.321
3
R
Thresh
I
Thresh
4.0
3.6
5.4
4.0
55
+1
6.0
5.3
kΩ
mA
dB
Note 1.
Note 1
Notes 1,2. See
Figure 2
dB
dB
dB
Notes 1,2
Notes 1,2
Notes 1,2
PSRR
CMRR
40
40
F
LLJ
F
LJL
F
HLJ
F
HJL
53
20
800
500
65
Hz
Hz
kHz
kHz
dB
Ω
Ω
Notes 1,2
Notes 1,2
Notes 1,2
Notes 1,2
Note 1
9
10
11
12
Z
I
Z
OJ
300
604
† Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
‡ Typical figures are at 25°C with nominal+ 5V supplies and are for design aid only: not guaranteed and not subject to production testing.
Note 1: 754Ω connected between JUNCTOR (pin 16) and OV.
Note 2: 604Ω connected between TIP (pin 1) and RING (pin 3).
2-36
Preliminary Information
DC Electrical Characteristics
Characteristics
1
S
U
P
P
L
Y
MH88500
.
Sym
V
A1
,V
A2
V
B
V
C1
,V
A2
I
A1
Min
-13
-30
Typ
‡
-24
Max
+13
Units
V
V
V
mA
mA
mA
mA
mA
V
V
Test Conditions
Operating Supply Voltages
-20
Operating Supply Currents
I
A2
I
B
I
C1
I
C2
High Level Input Voltage
MUTE
RC
V
IH
2
7
8
6
.2
.1
4.2
3
.8
1
3
V
IH
V
IL
4
5
I
N
P
U
T
S
Low Level Input Voltage
MUTE
RC
High Level Input Current
MUTE
RC
Low Level input Current
MUTE
RC
Sink Current
LED
RD
V
V
IL
I
IH
I
IH
I
IL
I
IL
I
LED
I
RD
I
RLY
V
OH
V
OL
I
OH
I
OL
-28
700
100
1
2
65
65
6
-6.5
10
10
6
100
100
µA
µA
µA
µA
mA
mA
mA
V
V
µA
µΑ
V
OFHK
, -6V
CD=RC=5V,RGD=0V
V
RRD
<1.5V
RC=RGND=0V,
CD=5V V
RRD
<1.5V
LED Unconnected
LED Unconnected
6
7
8
9
10
11
12
O
U
T
P
U
T
S
Diode Clamp Current
High Level Output Voltage
Low Level Output Voltage
OFHK
High Level Output Current
Low Level Output Current
‡ Typical figures are at 25°C with nominal+ 5V supplies and are for design aid only: not guaranteed and not subject to production testing.
TRANSHYBRID
LOSS
(dB)
10
20
30
40
50
60
550
600 650
700 750
800
850
900
950
LOAD IMPEDANCE ON JUNCTOR (Ω)
Figure 4 - Return Loss VS Junctor Load Impedance
2-37
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