2-129
Features
Transformerless 2-wire to 4-wire conversion
Battery Feed
Ringing & Messaging Facility
Power Down with Wake Up output
Automatic Ring Trip
Programmable Constant Current
Earth Ground Button detection
Switch Hook detection
Interface for a programmable CODEC
Ring ground over-current protection
Impedance reflection
Loop Length Indication
Applications
Line Interface for
PABX
Intercoms
Key Telephone Systems
Control Systems
Description
The SLIC provides a complete interface between an
industry standard programmable CODEC or DSP
and a subscriber loop.
Functions provided include battery feed, zero
crossing ring control, programmable current feed,
power down with wake up signal, cadenced
messaging facility, switch hook & dial pulse
detection, loop length indication and the capability of
reflecting a programmable CODEC's impedance or
supplying a standard 600 ohm impedance to the line.
The device is fabricated as a thick film hybrid using
various technologies for optimum circuit design high
reliability.
Figure 1 - Functional Block Diagram
2W-4W
Converter
Loop
Supervision
Line Drivers
&
Battery Feed
Constant
Current
Control
Switch
Circuits
VX
VR
SHK
EGB
LA
RE
MSE
PD
V
MSG
V
RNG
V
EE
V
DD
V
BAT
A
GND
B
GND
TIP
RING
Loop
WU
LCA
ISSUE 2
April 1995
Ordering Information
MH88614 30 Pin SIL Package
0
C to 70
C
MH88614
Programmable CODEC SLIC
Advance Information
MH88614
Advance Information
2-130
Figure 2 - Pin Connections
Pin Description
Pin #
Name
Description
1
IC
Internal Connection
2
IC
Internal Connection
3
TIP
Connects to the "Tip" lead of the telephone line.
4
IC
Internal Connection
5
RING
Connects to the "Ring" lead of the telephone line
6
LOOP
Loop Length Indication. The output on this pin is proportional to the loop length /
resistance, and is valid for off hook conditions only.
7
BGND
Battery Ground. This pin is the return pin for the battery feed to the line and also for the
message voltage supply and the Ring Voltage supply. This pin should normally be
connected to AGND.
8
WU
Wake Up(Output). When in the power down mode this pin goes high to indicate the phone
has gone off hook. When this occurs the power down signal should be removed.
9
EGB
Earth Ground Button Detection (Output) This output goes low when the ring lead or tip
lead is grounded.
10
IC
Internal Connection
11
VBAT
Battery Feed Supply. This pin is the supply for the line feed. (Typically -48V).
12
IC
Internal Connection
13
PD
Power Down (Input) Applying a logic 0 (Active low) will Power down the hybrid. This may
be used, but must be removed to allow a call to be made or to reduce power consumption.
14
AGND
Analog Ground. This pin is the return pin for the positive and negative supplies and is
normally connected to BGND.
15
VDD
Positive Supply. (Typically +5V).
16
VEE
Negative Supply. (Typically -5V).
17
IC
Internal Connection
18
VR
Receive (Input). The audio input signal is applied to this pin from the programmable
CODEC. This signal is internally a.c. coupled
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
IC
IC
TIP
IC
RING
LOOP
BGND
WU
EGB
IC
VBAT
IC
PD
AGND
VDD
VEE
IC
VR
IC
VX
IC
LCA
IC
LA
IC
VRING
VMSE
RE
MSE
SHK
2-131
Advance Information
MH88614
Pin Description- (Continued)
Pin #
Name
Description
19
IC
Internal Connection
20
VX
Transmit (Output). The audio output signal appears on this pin and is internally a.c.
coupled. This signal is applied to the programmable CODEC.
21
IC
Internal Connection
22
LCA
Loop Current Adjust (input). The circuit has two constant current settings that are logic
selectable
23
IC
Internal Connection
24
LA
Loop Alarm (Output) When the loop impedance exceeds the maximum limits that the SLIC
can support for a specified voltage & current this output will go low. This indicates that the
SLIC will no longer support the line. Note: This pin will also pulse low if Loop Disconnect
Dialling is performed, and goes low when the phone is on hook.
25
IC
Internal Connection
26
VRING
Ring Voltage Supply. This pin is the supply for the Ringing signal to the telephone.
(Typically 90V
RMS
on -48V battery).
27
VMSE
Message Voltage Supply. This pin is the supply for the message signal to the telephone.
(Typically -100V)
28
RE
Ring Enable (Input). The ringing signal is applied across Tip & Ring by applying a logic 1 to
this pin while the phone is "On Hook". Ringing will be automatically stopped when the
phone goes "Off Hook" regardless of the state of the RE pin.
29
MSE
Message Signal Enable (Input). A cadenced signal can be applied to this pin which will
switch the V
MSG
voltage onto Tip & Ring. The output voltage is internally conditioned to
prevent bell tinkle on the telephone. This is automatically switched off when the phone goes
off hook.
30
SHK
Switch Hook (Output). The output of this pin goes low when the phone goes "Off Hook"
and can be used externally to switch MSE off.
Functional Description
The MH88614 is an ONS SLIC for use with a
programmable / intelligent CODEC or DSP. The SLIC
performs all of the normal interface functions
between the CODEC and the analog telephone set
whilst having such additional features as Earth
Ground Button Detection, message switching and
Ringing switching with zero crossing.
The MH88614 is available as a 30 pin SIL package
to increase board densities.
2 Wire to 4 Wire Conversion
The hybrid performs 2 wire to 4 wire conversion by
taking the 4 wire signal from the programmable
CODEC at VR and converting it to a 2 wire
differential signal at Tip & Ring. The 2 wire signal
applied across Tip & Ring by the phone is converted
to 4 wire signal at Vx which is the output from the
SLIC to the programmable CODEC. Both the VR
input & Vx output are internally a.c. coupled.
Loop Supervision
The Loop Supervision circuit monitors the state of
the phone line and provides three different output
stages.
When the phone goes "Off Hook" the SHK pin goes
low to indicate this state. This pin reverts to a high
state when the phone goes back "On Hook" (see
figure 3).
When the phone is off hook the circuitry can also
detect two other features of the line status namely
Earth Ground Button & Loop Alarm.
A logic low signal on the Earth Ground Button output
indicates that an earth ground path has been applied
to the Tip or Ring lead of the telephone. This function
can be used for recall operations on phone sets with
Earth Ground Buttons.
The Loop Alarm signal low to indicate that the R
Loop
has been exceeded and that the circuit will no longer
support the line.
2-132
MH88614
Advance Information
The hybrid also provides an output which is
proportional to the loop length / resistance. LA must
be high for I
Loop
to be valid.
Where V
Loop
= the voltage at Loop
I
Loop
= the programmed line current
Constant Current Control
Whilst working within the R
Loop
maximum limit set by
the I
Loop
& V
Bat
levels chosen the circuit allows the loop
current to be set to one of the two discrete levels by
the use of the loop current adjust pin. Applying a logic
low to this pin sets the constant current to the lowest
level. By changing the level to a logic high the constant
current is set to the highest level. This feature can be
used with the loop alarm signal when setting up the
line to chose the loop current setting most suitable.
Line Drivers & Battery Feed
The Line Drivers & Battery Feed circuit provide
power to the line and allow bi-directional audio
transmission.
The line impedance present by the line driver
circuitry is a nominal 600 ohms, allowing the circuit
to be used on its own in a PABX application. The
nominal impedance can be modified to look like a
complex impedance such as those used within
R
Loop
= - [(10 x V
Loop
)-1.5]
I
Loop
- 82
Europe by allowing an impedance to be reflected
through the SLIC from the CODEC or DSP module.
The outputs at tip & ring protected from short term
over voltage between tip & gnd, ring to gnd or tip to
ring reducing the requirement for secondary
protection circuitry.
There is also long term protection on the outputs
against short circuits applied across tip & ring, tip to
gnd, ring to gnd and tip & ring to gnd.
Switch circuits
There are three switches built into the functionality of
this circuit, they are Ringing Enable, Message Signal
Enable and Power Denial.
Ringing Enable allows a logic level to be applied to a
pin and the ringing voltage superimposed on a d.c.
level to then be switched onto the line. The ringing
signal applied to the line at zero voltage crossing and
switched off at zero current. (see figure 3). The
ringing signal can be terminated by either returning
the Ringing Enable pin to a logic low level or it will
automatically stop when the phone goes off hook
regardless of the state of the input pin.
The Message Signal Enable pin provides the
switching control of the message voltage. A logic
high on the MSE pin applies the message voltage to
the line. Internal circuitry allows the input signal to
MSE to be cadenced, causing the output signal to be
cadenced, without causing bell tinkle. This is
possible by conditioning the rising and falling edges
of the output signal. Message Signal Enable also has
auto trip facility.
Figure 3 - Call Supervision
RE
I
RING
SHK
I
LOOP
1
0
30/45mA
0mA
On Hook
Off Hook
t
t
t
t
2-133
Advance Information
MH88614
When applying ringing and message signal to the
phone the two signals should be applied separately
to minimise total power consumption. Figure 4
indicates how the timing of this process could best
be achieved for cadenced and uncadenced message
signalling.
Power Denial can be applied at any time to remove
the line from service. The Power Denial input
enables the line to be isolated from the battery under
fault conditions or for maintenance purposes. A logic
low will remove the battery feed whilst a logic high
will provide power to the line.
Figure 4 - Call & Message Indication
MSE
Uncadenced
MSE
cadenced
RE
trdr
trda
trdr
trda - MSE should be removed at least 200ms before applying RE.
trdr - RE should be removed at least 120ms before applying MSE.
Absolute Maximum Ratings
*
* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
Parameter
Symbol
Min
Max
Units
Comments
1
DC Supply Voltage
V
DD
V
EE
V
BAT
-0.3
+0.3
0.3
+15
-15
-60
V
V
V
2
Ringing Voltage
V
RING
130
V
RMS
3
Message Voltage
V
MSG
-180
V
V
DC
+ AC
PEAK
4
Overvoltage Tip/Gnd
Ring/Gnd, Tip/Ring
300
V
MAX 1ms
(with power on)
5
Ringing Current
I
RING
45
mA
6
Message Current
I
MSG
6
mA
7
Short Circuit current
(continuous),
Tip/Gnd, Ring/Gnd, Tip/Ring
60
mA
8
Storage
Temp
T
STG
-40
+100
C
9
Package Power
Dissipation
P
DISS
2.5
W
T
AMB
70
C max
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