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Электронный компонент: MH88612B

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2-121
Features
Input impedance 600
Transformerless 2-wire to 4-wire conversion
Battery and ringing feed to line
Off-hook and dial pulse detection
Ring ground over-current protection
Adjustable constant current feed
Relay drive output with diode protection
Power Denial
Wide V
BAT
Operating Range
Tip/Ring Reversal
Applications
Line interface for:
PABX
Intercoms
Key Telephone Systems
Control Systems
Figure 1 - Functional Block Diagram
VBat
VDD VEE GNDA
VR
VX
VRef
CAP
SHK
RD1
RC1
VRLY
RC2
RF
RING
TIP
TF
Relay
Drive
Circuit
Over Current
Protection
2-Wire to
4-Wire
Conversion
Loop
Supervision
Current
Constant
Feed
Power
Denial
Battery
Feed
T/R
Reverse
T/R Reverse
Relay Driver
PD
LPGND
RV
Ordering Information
MH88612K 30 Pin SIL Package
0
C to 70C
Description
The SLIC provides a complete interface between a
switching system and subscriber loop. Functions
provided include battery feed, ringing feed and tip-
ring reversal to the subscriber line, 2-Wire to 4-Wire
hybrid interfacing, constant current feed and dial
pulse detection. The device is fabricated as a thick
film hybrid using various technologies.
DS5066
ISSUE 3
April 1995
MH88612K
Subscriber Line Interface Circuit
Preliminary Information
2-122
MH88612K
Preliminary Information
Figure 2 - Pin Connections
Pin Description
Pin #
Name
Description
1
TF
Tip Feed. Connects to external diode for protection. Internally connected to pin 21.
2
RF
Ring Feed (Input). is normally connected to ring relay for negative battery feed voltage
and ringing voltage input.
3
IC/NC
No Connections to be made to this pin, used for internal connection.
4
IC/NC
No Connections to be made to this pin, used for internal connection.
5
IC/NC
No Connections to be made to this pin, used for internal connection.
6
IC/NC
No Connections to be made to this pin, used for internal connection.
7
IC/NC
No Connections to be made to this pin, used for internal connection.
8
TIP
Connects to the "Tip" lead of the telephone line.
9
IC/NC
No Connections to be made to this pin, used for internal connection.
10
RING
Connects to the "Ring" lead of the telephone line.
11
RC2
Relay Control 2 (Input). Active high to reverse Tip/Ring.
12
LPGND
Loop Ground is the system ground reference with respect to V
Bat
. Normally tied with
GNDA.
13
IC/NC
No Connections to be made to this pin, used for internal connection.
14
VR
Voice Receive (Input) is the 4-wire analog signal to the SLIC.
15
VRef
Voltage Reference (Input). to set the constant current feed to the subscriber line.
Constant current feed can be adjusted by the input voltage on the V
Ref
. This pin can also be
grounded for normal 25mA loop current.
16
CAP
Connects external capacitor to ground for ring trip.
17
SHK
Switch Hook Detect (Output). Active high
18
GNDA
Analog Ground (0V)
19
VEE
Negative Power Supply Voltage (-5V).
20
VDD
Positive Power Supply Voltage (+5V).
21
TF
Tip Feed. Connect an external diode for protection. Internally connected to pin 1.
22
VBat
Negative Battery Feed Supply Voltage (-48V).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
TF
RF
IC
IC
IC
IC
IC
TIP
IC
RING
RC2
LPGND
IC
VR
VRef
CAP
SHK
GNDA
VEE
VDD
20
21
22
23
24
25
26
27
28
29
30
TF
VBat
RV
PD
VX
IC
IC
VRLY
RC1
RD1
2-123
Preliminary Information
MH88612K
23
RV
Ring Feed Voltage connects to (RF) through a normally closed ring relay.
24
PD
Power Denial (Input). A logic high will isolate the battery voltage to tip/ring.
25
Vx
Voice Transmit (Output). is the 4-wire analog signal from the SLIC.
26
IC/NC
No connections to be made to this pin, used for internal connection.
27
IC/NC
No connections to be made to this pin, used for internal connection.
28
VRLY
Relay Voltage Supply (+5V). This pin is used to power the on board relay.
29
RC1
Relay Control 1 (Input). Active high. Normally used for ringing.
30
RD1
Open collector sinks current when RC1 is at logic high.
Pin Description (Continued)
Pin #
Name
Description
Functional Description
The SLIC performs a transformerless 2-wire to 4-
wire conversion of the analog signal. The 2-wire
circuit is the balanced line going to the subscriber
loop, while the 4-wire circuit is the audio signal going
to and from devices such as the voice codec or
switching circuit. The SLIC also provides a switch
hook (SHK) status output which goes high when the
telephone is set off-hook.
Constant Current Feed
The SLIC employs a complex feedback circuit to
supply a constant feed current to the line. This is
done by sensing the sum of the voltages across the
internal feed resistors and comparing it to an input
reference voltage (V
Ref
) that determines the constant
feed current. If V
REF
is externally grounded, the
constant current is set at 25mA. For a constant
current setting between 18mA and 30mA. V
Ref
can
be set between 8.75 Vdc and -6.35 Vdc. The
relationship is defined by the equation:
I
Loop
= 25 - V
Ref
mA (
2 mA)
1.25
Switch Hook Detection
When the DC current exceeds an internal threshold
level, the switch hook (SHK) will go high. If the loop
resistance is so high that V
BAT
can no longer supply
the required amount of loop current as determined
by constant current supply circuit, the output of the
switch hook (SHK) will go low to indicate that the
loop resistance is too high and the line is on hook.
Ringing And Ring Trip Detection
In Figure 3 a ringing signal (e.g., 90 Vrms +-48 Vdc
is applied to the line by disconnecting (RV) from
(RF), and connecting the ringing voltage at (RF) by
use of the relay K1. An internal clamp diode is
provided between VRLY and RD1.
The SLIC can detect an off-hook condition during
ringing but there is a large AC component which
must be filtered out to give a true off-hook condition
at SHK.
A 1.0
F capacitor connected from (Cap) to ground
will provide adequate attenuation when ringing is
applied. Once an off-hook condition has been
detected a logic high should be applied to (RC)
which will activate the relay (K1) to disconnect the
ringing voltage from (RF) and reconnect to (RV). At
that time SLIC will revert to constant current feed
operation.
For applications requiring Dial Pulse Detection the
Capacitor connection to ground should be controlled
such that the capacitor is only connected during
ringing. During off-hook conditions (closed loop), the
capacitor should be switched out. This can be
performed using a transistor, relay to system drive
output of a codec. Applying GNDA to the Ring Trip
Filter Control pin will switch in the filter, whilst
removing GNDA, (with the switch in a tristate
condition), will switch out the filter.
For applications using DTMF signalling, the
capacitor can be permanently connected to ground.
Tip/Ring Reverse
The MH88612K provides a Tip/Ring reversal relay
driver. To activate the internal relay to reversal Tip
and Ring apply a logic input to RC2.
Current Limit
The Tip or Ring may be accidentally shorted to
ground. In such a case, current will only flow through
the feed resistor. This high current will be sensed
2-124
MH88612K
Preliminary Information
and reduced by the current limit circuit to a lower
value to protect the internal circuitry.
Receive Gain
The power denial function is a feature of the
MH88612C which allows for powering down of the
subscriber loop. A logic high input applied to the
power denial pin effectively removes the battery
voltage from the loop driver circuitry. The resulting
I
Loop
is negligible and power consumption is
minimised. The power denial function is useful for
disabling a loop which may have a ground fault. This
pin should be held low when not in use.
Applications
Component List
R1
= 1/4 W, + 10%, 200
R2
= 1/4 W, + 5%, 470
C1
= Cap. elec., 1.0
F, + 10%, 25V
D1,D2,D3,D4
= Diode Rect., 200V, 1A, IN4003
K1
= Relay E/M, 5 or 6V, 1 form C
Decoupling capacitors (Cap. Cer 0.1
F, 50% + 20%) should be added to V
DD
, V
EE
, V
Bat
, V
Ref
and V
RLY
Options RV1, RV2 = 160V Vrms, 250V, 10J
Figure 3 - Application Circuit
VR
VX
VRef
SHK
CAP
GNDA
VEE
VDD
VBat
RD1
RC2
RC1
RING
TIP
TF
RV
RF
VBat
VBat
C1
R1
RV1
RV2
K1
D1
D2
D3
D4
90 VRMS
SUPERIMPOSED
ON -48VDC
+
-
-5V
+5V
-48V
+5V
MH88612K
VRLY
PD
Tip
Ring
K1
Ring Trip
Filter
Control
R2
2-125
Preliminary Information
MH88612K
Absolute Maximum Ratings*
* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
Typical figures are at 25C and are for design aid only.
Parameter
Symbol
Min
Max
Units
1
DC Supply Voltage
V
DD
V
EE
V
Bat
-0.3
+0.3
0.3
+15
-15
-60
V
V
V
2
Storage Temperature
T
STG
-40
100
C
3
Package Power Dissipation
P
D
2
W
Recommended Operating Conditions
Characteristics
Sym
Min
Typ
Max
Units
Comments
1
Operating Supply Voltage
V
DD
4.75
5.0
5.25
V
V
EE
-4.75
-5.0
-5.25
V
V
Ref
0
V
Adjustable
V
Bat
-27
-48
-60
V
V
RLY
5
V
2
Operating Temperatures
T
O
0
70
C