2-63
Features
Differential to single ended conversion
Transformerless 2-2 wire conversion
Minimum installation space
Off-Hook detection and LED indicator drive
Relay drive output
Battery and ringing feed to line
Logic interface: MUTE, SHK, RRC
Mute of incoming audio
Dial pulse detection
Voltage surge protection
German complex input impedance
Applications
Line Interface for:
Intercoms
Key Systems
PABX
Description
The Mitel MH88520-1 German 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
MH88520-1 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' (SIL) package allowing
optimum circuit board packing density and very high
reliability.
Relay Drive
Circuit
JUNC
MUTE
SHK
LED
THRESH ADJ
TIP (A)
RING (B)
RING FEED 1
RING FEED 2
VRLY
RRD
RRC
RGND
Speech Circuit
Loop Detection
Loop Feed/
Ring Feed
VBAT AGND
VDD
VEE
ISSUE 4
April 1995
Ordering Information
MH88520-1
20 Pin SIL Package
0
C to 70
C
Figure 1 - Functional Block Diagram
MH88520-1
German Subscriber Line Interface Circuit (SLIC)
Preliminary Information
2-64
MH88520-1
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
IC
Internal Connection. Leave open circuit.
3
RING
Ring Lead. Connects to the "Ring" lead (B-wire) of the telephone line.
4
RF1
Ring Feed 1. Connect to the Ring Relay contact. See Figure 5.
5
IC
Internal Connection. Leave open circuit.
6
RF2
Ring Feed 2. Connect to normally closed contact of Ring Relay. See Figure 5.
7
IC
Internal Connection. Leave open circuit.
8
V
EE
Negative Power Supply Voltage. Normally -5V.
9
LED
LED Drive (Output). Drives an LED directly. A logic low indicates an off-hook condition.
10
SHK
Switch Hook Detect (Output). A logic low indicates an off-hook and dial pulsing
condition. Open collector output with 10k
internal pull up to V
DD
.
11
THRESH ADJ
Allows adjustment of SHK detection threshold as shown in Figure 6.
12
V
DD
Positive Power Supply Voltage. Normally +5V. This provides current for both internal
circuitry as well as the loop.
13
AGND
Analog Ground. Supply and Battery Ground.
14
V
BAT
Battery Supply Voltage. Normally -24V. This provides current to the loop.
15
MUTE
MUTE (Input). A logic low will mute signals coming from Tip-Ring to the JUNC pin.
16
JUNC
JUNCTOR. Ground (AGND) referenced transmit and receive speech path.
17
RRD
Ring Relay Drive (Output). Connects to the ring relay coil. A logic low activates the
relay.
18
RGND
Relay Ground. Return path for relay supply voltage. Normally connected to AGND.
19
RRC
Ring Relay Control (Input). A logic high activates the Ring Relay Drive (RRD) outputs.
20
VRLY
Relay Positive Supply voltage. Normally +5V. Connects to the relay coil and the relay
supply voltage. An internal clamp diode from VRLY to GRND is provided.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
TIP
IC
RING
IC
RF2
IC
VEE
LED
SHK
THRESH ADJ
VDD
AGND
VBAT
MUTE
JUNC
RRD
RGND
RRC
VRLY
RF1
2-65
Preliminary Information
MH88520-1
Functional Description
The BORSH Functions
The MH88520-1 performs all of the Borsh functions
of Battery Feed Overvoltage Protection, Ringing,
Supervision and Hybrid (2-2 Wire).
Return Loss at Tip-Ring
To maximise return loss, the impedance at Tip-Ring
should match the SLIC's impedance (220R + 820R //
115nF). However, the SLIC's input impedance is
dependent on the JUNCTOR termination resistance.
Therefore the JUNCTOR must be terminated with
754
.
Figure 3 illustrates a typical connection between two
SLICs through two crosspoint switches. Optimum
return loss occurs when the JUNCTOR is terminated
with 754
. Since the JUNCTOR input/output
impedances is 604
and the crosspoint switch
resistances are 75
+ 75
, this configuration gives
optimum return loss as shown in Figure 4.
Hybrid
The 2-2 wire hybrid circuit converts the incoming
balanced signal at Tip and Ring of the telephone line
into a ground referenced output signal at JUNC of
the SLIC, and converts the ground referenced input
signal at JUNC of the SLIC into the non-balanced
output signal at Tip-Ring of the telephone line.
Mute
A logic low at the MUTE input results in muted
signals coming from Tip and Ring to the JUNC
terminal while allowing signals from the JUNC
terminal to Tip and Ring to be transmitted.
Overvoltage Protection
The MH88520-1 is protected from short term (1ms)
(+250V) between Tip and Ring, Tip and Ground, and
Ring and Ground. However, additional protection
circuitry may be needed depending upon the
requirements which must be met for the final
equipment.
Loop Detection
The loop detection circuit determines whether a low
enough path is across Tip and Ring to be recognised
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. When an off-hook condition
occurs the SHK and LED outputs toggle to a logic
low level. These outputs also toggle during incoming
dial pulses.
Figure 3 - SLIC Crosspoint Switch Connection
MH88520-1
MH88520-1
TIP
RING
TIP
RING
TIP
RING
TIP
RING
JUNC
JUNC
75
75
CROSSPOINT
SWITCH
CROSSPOINT
SWITCH
16
16
1
3
1
8
SLIC 1
SLIC 2
2-66
MH88520-1
Preliminary Information
Ringing
The relay drive circuit switches ringing onto Ring
Feed (Fig. 7). The diode is present to suppress
voltage transients during relay switching caused by
the inductive coils of the relay. Ringing voltage
included ac ringing (90V
RMS
typically) and DC line
feed voltage (-24V typically).
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
dc
(although for ac it is optimised for a German complex
impedance) which gives the loop current as:
Voltage at Ring Feed pin
Amps
Telephone Impedance + 600
The positive supply for the line feed circuit is VDD
though the loop current is determined from Ring
Feed and GND.
Line Impedance
The MH88520-1's Tip-Ring (Zin) impedance is fixed
at the German complex impedance. For correct SLIC
impedance, JUNC must be appropriately terminated.
See AC Electrical Characteristics.
Transmit and Receive Gain
Transmit Gain (JUNC to Tip-Ring) and Receive Gain
(Tip-Ring to JUNC) are fixed (See AC Electrical
Characteristics). For correct gain, the SLIC input
impedance must match theline impedance and
JUNC must be appropriately terminated.
Digital Applications
The 2-wire junctor output can be converted to a
4-wire circuit using the MH88524 (2-4 wire
converter). This 4 wire circuit can be interfaced to a
filter/codec to use in digital voice switched systems.
Alternatively the MH88600/MH88612, digital ONS
SLIC can be used.
Figure 4 - Return Loss VS Junctor Load Impedance
10
20
30
40
50
60
550
600
650
700
750
800
850
900
950
TYPICAL
RETURN
LOSS
LOAD IMPEDANCE ON JUNCTOR (
)
(dB)
2-67
Preliminary Information
MH88520-1
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: German Impedance connected between TIP (A) (pin 1) and RING (B) (pin 3).
Parameter
Symbol
Min
Max
Units
1
Voltage Supplies
Referenced to GND
V
DD
-0.3
+15
V
V
EE
-15
0.3
V
V
Bat
-35
0.3
V
2
Clamp Diode Breakdown Voltage-V
Ref
to RGND
V
RLY
+32
V
3
Operating Temperature
T
AMB
0
+70
C
4
Storage Temperature
T
S
-55
+125
C
5
Power Dissipation
P
D
4
Watt
AC Electrical Characteristics
Voltages are with respect to ground (V
SS
), TA = 25C, unless otherwise stated.
Test conditions unless noted, V
DD
=5V, V
EE
=-5V, V
Bat
=-24V).
Characteristics
Sym
Min
Typ
Max
Units
Test Conditions
1
Junctor to Differential Output
(tip-ring) Gain
-7.0
0
dB
1kHz, 0.5V source on
pin 16. Note 2
2
Differential; Input (tip-ring) to
Junctor Gain
0.0
dB
1kHz, 0.5V
Source
Applied on pins 1&3
Note 1, 2
3
On/Off Hook Detection Threshold
Loop Current
I
Thresh
8.0
10
12
mA
Note 1
4
Transhybrid Loss
30
dB
Notes 1,2
5
Passband Frequency Response
1.0
dB
Notes 1,2
200Hz - 3400Hz
6
Power Supply V
BAT
Rejection Ratio
V
DD
(@ Junctor) V
EE
PSRR
PSRR
PSRR
30
40
40
dB
dB
dB
Notes 1,2. Ripple
0.1V 1kHz
7
Common Mode Rejection Ratio
(Tip and Ring to Junctor)
CMRR
40
dB
Notes 1,2
1kHz, 0.5V
8
Longitudinal Balance
46
50
dB
Notes 1
9
Junctor Output Impedance
Z
OJ
604
10
Return Loss at Tip, Ring
18
30
dB
1kHz Notes 1,2
11
Max. Signal Level
3
dB
Notes 1,2
12
Max. Ringing Voltage
105
V
RMS
13
Max. Ringing Frequency
25
60
z
14
Idle Channel Noise
at T-R
at Junctor
N
TR
N
J
-80
-80
-70
-75
dBmp
dBmp
Notes 1,2
15
Mute Attenuation
30
dB
Notes 1,2
2-68
MH88520-1
Preliminary Information
.
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.
MH88520 Input Impedance
Characteristics
Sym
Min
Typ
Max
Units
Test Conditions
1
S
U
P
P
L
Y
Operating Supply Voltages
V
DD
V
EE
V
Bat
4.5
-5.5
-30
5
-5
-24
5.5
-4.5
-20
V
V
V
2
Operating Supply Currents
I
DD
I
EE
I
Bat
8
6
1
mA
mA
mA
On Hook
3
I
N
P
U
T
S
High Level Input Voltage
MUTE
RRC
V
IH
V
IH
2.0
4.5
V
V
4
Low Level Input Voltage
MUTE
RRC
V
IL
V
IL
0.8
0.5
V
V
5
High Level Input Current
MUTE
RRC
I
IH
I
IH
-28
700
A
A
6
Low Level Input Current
MUTE
RRC
I
IL
I
IL
100
10
A
A
7
O
U
T
P
U
T
S
Sink Current
LED
RRD
I
LED
I
RRD
65
1.5
100
200
mA
mA
V
RLY
= RRC= 5V
RGND = 0V
V
RRD
< 1.5V
8
Relay to V
DD
Diode Clamp Current
I
RLY
65
100
mA
RRC=RGND=0V
V
RLY
= 5V
V
RRD
> 4.5V
9
High Level Output Voltage
SHK
V
OH
4.5
5
5.5
V
LED Unconnected
10
Low Level Output Voltage
SHK
V
OL
0
.01
0.7
V
LED Unconnected
11
Low Level Output Current
I
OL
4
A
12
Power Consumption
P
C
mW
400
Loop
13
Max. Operating loop
R
L
R
L
600
900
at 18mA, 24V
at 18mA, 30V
Variant
Country
Impedance
01
GERMANY
220
+ 820
// 115nF
2-69
Preliminary Information
MH88520-1
Figure 5 - Typical Application Circuit
Figure 6 - Off-Hook Threshold Adjust
TIP
RING
RINGING
GENERATOR
90VRMS
Optional
Protection
Circuit
K1
R1
-24V
-5V
C1
C2
+5V
K1
DS1
AUDIO
INPUT/OUTPUT
MUTE CONTROL
INPUT
SWITCH HOOK
OUTPUT
OFF-HOOK LED
RING CONTROL
INPUT
TIP
RING
RF1
RF2
VBAT
VEE AGND VDD RGND
VRLY
RRD
LED
SHK
MUTE
JUNC
RRC
1
3
4
6
14
8
13
12
18
20
17
19
9
10
15
16
MH88520-1
Notes:
R1= 200
, 1/4W, 5%
K1= Relay E/M 5V, 1Form C
C1, C2 = 0.1uF, 50V, Ceramic
Earth Ground
RV
RG
GND
SLIC
THRESH
ADJ
SLIC
11
11
VBAT
THRESH
ADJ
60
50
40
30
20
10
2
3
4
5
6
400
200
10
15
20
25
R
R
(k
)
(k
)
RG = 6000 x I
VDD - (501 x I)
RV= (100 x VDD) - (6000 x I)
(501 x I) - VDD
R and R
THRESH
(k
)
R and R
THRESH
(k
)
RG(k
)
(a)
RV(k
)
(b)
7
8
I = Threshold current
in Amps
V
DD
= +5V
2-70
MH88520-1
Preliminary Information
Figure 7 - Relay Drive Circuit
TIP(a)
RING
RING FEED 1
VRLY
RRD
RGND
RELAY COIL
LINE FEED/
RING FEED
CLAMP DIODE
RELAY
DRIVE
CIRCUIT
V
DD
HYBRID
RRC
-24VDC
+90VAC
RING FEED 2
+5V
2-71
Preliminary Information
MH88520-1
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
MH88520-1
MH88520-1
MH88520-1
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
2-72
MH88520-1
Preliminary Information
Figure 9 - Mechanical Data
2.00+ 0.020
(50.8 + 0.5)
0.58+0.02
(14.7+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)
0.8 + 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.
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