2-43
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
Applications
Line Interface for:
PABX
Intercoms
Key Systems
Description
The Mitel MH88500IN 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 MH88500IN 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.
Figure 1 - Functional Block Diagram
JUNCTOR
MUTE
OFHK
LED
THRESH ADJ
V
C2
V
A2
V
B
V
C1
GND
VA
1
TIP
RING
RING
FEED
CD
RD
RC
RGND
V
A2
V
B
Speech Circuit
Loop Detection
Loop Feed/
Ring Feed
Relay Drive
Circuit
ISSUE 1
April 1995
Ordering Information
MH88500IN
20 Pin SIL Package
0
C to 70
C
MH88500IN
Hybrid Subscriber Line Interface Circuit (SLIC)
Preliminary Information
2-44
MH88500IN
Preliminary Information
Figure 2 - Pin Connections
Pin Description
Pin #
Name
Description
1
TIP
Tip Lead. Connects to the "Tip" lead (A-wire) of the telephone line.
2
V
A1
Positive Line Feed Supply Voltage. Normally connected to V
A2
.
3
RING
Ring Lead. Connects to the "Ring" lead (B-wire) of the telephone line.
4
RING FEED
Negative Line Feed Voltage and Ringing Input. Normally connected to Ring Relay.
5
IC
Internal Connection. Leave open circuit. Use for testing only.
6
V
C1
Sense Input. Normally connected to negative line feed voltage supply.
7
GND
Analog ground (0V). Internally connected to pin 13.
8
V
B
Negative Analog Supply Voltage.
9
LED
LED Drive Output. Drives an LED directly. Off-Hook condition, logic low.
10
OFHK
Logic Low Output. Indicates closed loop condition (Off-Hook and dial pulsing).
11
THRESH ADJ
Allows adjustment of OFHK detection threshold.
12
V
A2
Positive Power Supply Voltage. Normally connected to V
A1
.
13
GND
Analog Ground (0V). Internally connected to pin 7.
14
V
C2
Loop Detector Voltage Supply.Connected to negative line feed voltages supply.
15
MUTE
Input mutes the incoming audio. Active low.
16
JUNCTOR
Receive/transmit audio speech path. (referenced to 0V GND)
17
RD
Relay Drive Output. Open collector sinks current when RC high. Diode clamp
protected.
18
RGND
Ground for Relay Drive Circuit.
19
RC
Ring Control Input. Active high.
20
CD
Clamping Diode. Normally connected to relay positive voltage.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
TIP
VA1
RING
IC
VC1
GND
V
B
LED
OFHK
THRESH ADJ
VA2
GND
VC2
MUTE
JUNCTOR
RD
RGND
RC
CD
RING FEED
2-45
Preliminary Information
MH88500IN
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 604
.
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.
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 = 5.4k
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.
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 600
which
gives the loop current as:
IL = Voltage at RING FEED pin Amps
Telephone Impedance + 600
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).
Figure 3 - SLIC Crosspoint Switch Connection
MH88500IN
MH88500IN
TIP
RING
TIP
RING
TIP
RING
TIP
RING
JUNC
JUNC
75
75
CROSSPOINT
SWITCH
CROSSPOINT
SWITCH
16
16
1
3
1
3
2-46
MH88500IN
Preliminary Information
Absolute Maximum Ratings
Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
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: 754
connected between JUNCTOR (pin 16) and 0V.
Note 2: 604
connected between TIP (pin 1) and RING (pin 3).
Parameter
Symbol
Min
Max
Units
1
Voltage Supplies - V
Ref
to GND
V
A1,
V
A2
V
V
B
-18
+18
V
V
C1
, V
C2
-35
V
2
Clamp Diode Breakdown Voltage-V
Ref
to RGND
V
CD
+15
V
3
Operating Temperature
T
AMB
0
+70
C
4
Storage Temperature
T
STG
-40
+100
C
5
Power Dissipation
P
D
1.2
Watt
AC Electrical Characteristics
Voltages are with respect to ground (V
SS
), TA = 25C, unless otherwise stated.
Test conditions unless noted, V
A1
=V
A2
=+7V, V
B
=8V, V
C2
=-24V(+5%).
Characteristics
Sym
Min
Typ
Max
Units
Test Conditions
1
Junctor to differential output (tip-
ring) gain.
A
JL
0.8
1.0
0
1.2
V/V
dB
1kHz, 400mV
RMS
source on pin 16.
Note 2
2
Differential Input (tip-ring) to
junctor gain
A
LJ
0.8
1.0
0
1.2
V/V
dB
1kHz, 1V
RMS
Source on pins 1&3.
Note 1,2
3
On/Off Hook Detection
Threshold
Loop Resist
Loop Current
R
Thresh
I
Thresh
4.0
3.6
5.4
4.0
6.0
5.3
k
mA
Note 1
Note 1
4
Trans Hybrid Loss
55
dB
Notes 1,2. See
Figure 2
5
Passband Linearity
+1
dB
Notes 1,2
6
Power Supply Rejection Ratio
(VC to Junctor)
PSRR
40
dB
Notes 1,2
7
Common Mode Rejection Ratio
(Tip and Ring to Junctor)
CMRR
40
dB
Notes 1,2
8
Low Frequency Cutoff (3dB)
Junctor to Line
Line to Junctor
F
LLJ
F
LJL
53
20
Hz
Hz
Notes 1,2
Notes 1,2
9
High Frequency Cutoff (3dB)
Line to Junctor
Junctor to Line
F
HLJ
F
HJL
800
500
kHz
kHz
Notes 1,2
Notes 1,2
10
Longitudinal Balance
65
dB
Note 1
11
Tip (or Ring) to ground AC input
impedance
Z
I
300
12
Junctor output impedance
Z
OJ
604
2-47
Preliminary Information
MH88500IN
.
DC Electrical Characteristics
Typical figures are at 25
C with nominal+ 5V supplies and are for design aid only: not guaranteed and not subject to production testing.
Figure 4 - Return Loss VS Junctor Load Impedance
Characteristics
Sym
Min
Typ
Max
Units
Test Conditions
1
S
U
P
P
L
Y
Operating Supply Voltages
V
A1
,V
A2
V
B
V
C1
,V
A2
-13
-30
-24
+13
-20
V
V
V
2
Operating Supply Currents
I
A1
I
A2
I
B
I
C1
I
C2
7
8
6
.2
.1
mA
mA
mA
mA
mA
3
I
N
P
U
T
S
High Level Input Voltage
MUTE
RC
V
IH
V
IH
4.2
3
V
V
4
Low Level Input Voltage
MUTE
RC
V
IL
V
IL
.8
1
V
5
High Level Input Current
MUTE
RC
I
IH
I
IH
-28
700
A
A
6
Low Level Input Current
MUTE
RC
I
IL
I
IL
100
1
A
A
7
O
U
T
P
U
T
S
Sink Current
LED
RD
I
LED
I
RD
2
65
6
100
mA
mA
V
OFHK
,-6V
CD=RC=5V,RGD=0V
V
RRD
<1.5V
8
Diode Clamp Current
I
RLY
65
100
mA
RC=RGND=0V,
CD=5V V
RRD
<1.5V
9
High Level Output Voltage
V
OH
6
V
LED Unconnected
10
Low Level Output Voltage
OFHK
V
OL
-6.5
V
LED Unconnected
11
High Level Output Current
I
OH
10
A
12
Low Level Output Current
I
OL
10
10
20
30
40
50
60
550
600
650
700
750
800
850
900
950
TRANSHYBRID
LOSS
(dB)
LOAD IMPEDANCE ON JUNCTOR (
)
2-48
MH88500IN
Preliminary Information
Figure 5 - Transhybrid Loss Test Circuit
Figure 6 - Off-Hook Threshold Adjust
5
1
3
16
1
5
16
604
604
VTR
VTR
VO
10
F
200
10H
54
VS
3
754
VX
CAN BE MEASURED THAT
V
TP
=2VX=2V
TR
(a)
TRANSHYBRID LOSS = - 20LOG (VO)
(b) 2VS
MH88500IN
MH88500IN
R
R
GND
MH88500IN
THRESH
ADJ
MH88500IN
11
11
VC2
THRESH
ADJ
120
100
80
60
40
20
1
2
3
4
5
6
2000
1000
10
20
30
40
R
R
(k
)
(k
)
R
THRESH
(k
)
(b)
R
THRESH
(k
)
(a)
(48 x R
THRESH
) -28.8
5.4 - R
THRESH
(912 x R
THRESH
) +604
R
THRESH
- 5.4
R and R
THRESH
(k
)
(a)
R and R
THRESH
(k
)
(a)
R =
R =
2-49
Preliminary Information
MH88500IN
Figure 7 - Relay Drive Circuit
TIP
RING
RING FEED
CD
RD
RGND
RELAY COIL
LINE FEED/
RING FEED
CLAMP DIODE
RELAY
DRIVE
CIRCUIT
+V
V
A1
MH88500IN
RC
-24VDC
-24VDC
+90VAC
2-50
MH88500IN
Preliminary Information
Figure 8 - PABX Typical Application
-24VDC
90VAC
-24VDC
-24VDC
90VAC
-24VDC
-24VDC
90VAC
-24VDC
-8V
-24V
0V
+7V
+5V
+5V
-8V
-24V
0V
+7V
+5V
+5V
-8V
-24V
0V
+7v
+5V
+5V
CONTROL
LOGIC
ADDRESS
OUT
00
01
02
03
04
05
06
07
A0
A1
A2
A0
A1
A2
00
01
02
03
04
05
06
07
A
0
-A
2
/D
0
-D
3
MT8812
Crosspoint
Switch
J
0
J
1
J
2
J
3
-L
7
L
0
MH88500IN
MH88500IN
MH88500IN
A0
A1
A2
SELECT
OUTPUT
D
0
D
1
D
2
|
|
D
7
2
12
9 20 17 4
1
3
TIP
RING
7
14
6
8
16
10
19
15
15
19
10
16
8
6
14
7
3
1
RING
TIP
4
17
20
9
12
2
15
19
10
16
8
6
14
7
RING
TIP
3
1
4
17
20
9
12
2
MD74SC137
1 OF 8
DECODER
MD74SC137
1 OF 8
DECODER
5 MORE
SLICS
5 MORE
SLICS
CMOS
4512
8-INPUT
MUX
2-51
Preliminary Information
MH88500IN
Figure 9 -Mechanical Data
2.00 + 0.020
(50.8 + 0.5)
0.52+0.02
(13.2+0.5)
0.12 Max
(3.1 Max)
0.010 + 0.002
(0.25 + 0.05)
0.080 Max
(2.0 Max)
Side View
*
0.05 + 0.01
(1.3 + 0.5)
*
*
*
0.05 + 0.02
(1.3 + 0.05)
0.020 + 0.05
(0.51 + 0.13)
0.100 + 0.10
(2.54 + 0.13)
0.18 + 0.02
(4.6 + 0.5)
1 2 3 4
19 20
Notes:
1) Not to scale
2) Dimensions in inches).
3) (Dimensions in millimetres).
*Dimensions to centre of pin &
tolerance non accumulative.
2-52
MH88500IN
Preliminary Information
Notes:
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