MH88617
Programmable SLIC with Ringing Amplification
Advance Information
Features
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Fully programmable line impedance,network
balance impedance and gains
Programmable loop current with long loop
capability
2-4 Wire conversion
Power down and wake up
Battery feed to line with wide operating range
Off-hook and dial pulse detection
Over-current protection
Integral ringing amplifier with auto ring trip
Tip/Ring reversal
Meter pulse injection
On-hook transmission to the line capability
Relay driver
Short loop ringing capability with low voltage
DC supply
DS5037
ISSUE 4
May 1999
Ordering Information
MH88617AV-PI 21PIN SIL Package
MH88617AD-PI 28PIN DIL Package
MH88617AS-PI 28PIN SM Package
MH88617AT-PI 21PIN 90° L/F Package
-40°C to 85°C
Description
The Mitel MH88617 is a highly featured, low cost
Subscriber Line Interface Circuit (SLIC). It provides a
total analog transmission and signalling link between
a CODEC and a subscriber line. All functions are
integrated into a single thick film hybrid module,
which provides high reliability and optimum circuit
design needing a minimum of external components.
The line impedance, network balance impedance,
gain and loop current are all externally
programmable, making the device suitable for a wide
range of applications worldwide.
Applications
Line interface for:
• PABX/Key Telephone System
• Analog Terminal Adaptors
• Pair Gain System
• Fibre in the Loop/Wireless Local Loop
VBAT
VCC VEE
GND
LCA
LR
Power
Management
Reversal
GVX
Constant
Current Control
2 - 4 Wire
Conversion
Supervision
Programmable
Impedance
ZA
Gain Adjust
& Programmable
Network Balance
TIP
VX
VR
TIP / RING
Drive and
RING
Sense
Ringing Control
and
Amplifier
Auto Ring Trip
Metering
Injection
Relay Driver
RDI
RC
RV DCRI
SHK
ESI
ESE
RDO
Figure 1 - Functional Block Diagram
2-157
MH88617
DCRI
RDI
TIP
IC
RING
IC
LR
RC
ESE
ESI
LCA
IC
IC
VBAT
IC
SHK
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28 Pin DIL
RDO
LR
TIP
RING
VBAT
LCA
VX
GVX
VR
VCC
AGND
VEE
RV
ESE
ESI
IC
SHK
RC
ZA
Advance Information
28
27
26
25
24
23
22
21
20
19
18
17
16
15
VX
GVX
DCRI
IC
IC
IC
VCC
AGND
VEE
ZA
RV
VR
RDI
RDO
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
21 Pin SIL
Figure 2 - Pin Connections
Pin Description
28
Pin
DIL
26
16
15
5
1
3
12
9
21
Pin
SIL
1
2
3
4
5
6
7
8
Name
DCRI
RDI
RDO
LR
TIP
RING
VBAT
LCA
Description
DC Ringing Voltage Input.
A continuous DC voltage is applied to this pin. This voltage
is the positive supply rail for the internal ringing amplifier.
Relay Driver Input.
Relay driver control pin.
Relay Driver Output.
Open collector relay driver output.
Line Reversal.
Setting this pin to a logic 0 will perform a line reversal. This pin must be
connected to logic 1 for normal operation.
Tip Lead.
Connects to the "Tip" lead of the subscriber line.
Ring Lead.
Connects to the "Ring" lead of the subscriber line.
Battery Voltage.
Battery supply for the subscriber line. Typically -48V DC is applied to
this pin.
Loop Current Adjust.
The loop current is programmed by connecting a resistor between
this pin and the VCC or AGND pins. Leaving this pin open circuit defaults the loop current
to 24mA. Setting this pin to 0V will apply power down.
Transmit Signal (Output).
4-wire analog signal from the SLIC.
Transmit Gain Adjust.
The transmit gain can be programmed by connecting a resistor
between this pin and VX. The Network Balance Impedance can also be programmed by
connecting external matching components from this pin to VR.
Receive Signal (Input).
4-wire analog signal to the SLIC.
Positive Supply Voltage.
+5V.
28
27
9
10
VX
GVX
17
22
21
20
11
12
13
14
VR
VCC
AGND
Analog Ground.
Ground path for the subscriber line and all DC power supplies,
normally connected to system ground.
VEE
Negative Supply Voltage.
-5V.
2-158
Advance Information
Pin Description (continued)
28
Pin
DIL
18
21
Pin
SIL
15
Name
RV
Description
MH88617
Ringing Voltage.
A low level AC sinusoid is applied to this pin. This signal is amplified
and output from TIP/RING to the line as the ringing signal, when RC is at logic 1. This pin
should be driven with a low impedance AGND centred source.
External Signal Enable.
Meter pulse input enable.
External Signal Input.
Meter pulse input.
Internal Connection.
No connection should be made to this pin.
7
8
2,
4,10
11,13
,23
25,24
16
17
18
ESE
ESI
IC
14
6
19
19
20
21
SHK
RC
ZA
Switch Hook Detect (Output).
A logic 1 at this pin indicates when the subscriber has
gone Off-Hook.
Ringing Control (Input).
A logic 1 will cause the ringing voltage to be applied to the line.
Line Impedance.
Connect passive components from ZA to ground to match input and
line impedance.
device to the line and the signal from the line to the
device. The signal input at VR being sent to the line,
must not appear at the output VX. In order to prevent
this, the device has an internal cancellation circuit,
the measure of this attenuation is Transhybrid Loss
(THL).
The MH88617 has the ability to transmit analog
signals from VR through to Tip and Ring when on-
hook. This can be used when sending caller line
identification information.
Functional Description
The MH88617 is a Subscriber Line Interface Circuit
(SLIC) used to provide an analog interface between
the 4-wire connection and the 2-wire subscriber line
of a communications system.
It provides powering of the subscriber line along with
signalling, control and status circuits. This combines
to provide a comprehensive line and interface
solution in applications such as PABX, Key Systems,
Analog Terminal Adapters, Pair Gain Systems, Fibre
in the Loop and Wireless Local Loop.
Battery Feed and Loop Current Adjust
The MH88617 has an active feedback circuit to
regulate the DC current to the subscriber line. This
current is programmable over a wide range via the
LCA pin. With LCA open circuit the current will be set
to 24mA. This can be increased up to 55mA by
connecting a resistor between LCA and VCC or
reduced down to 14mA by connecting a resistor
between LCA and AGND. MSAN-156 shows a table
of resistor values and loop current.
The line driver stage is biased between +5V and
-48V DC. Therefore it should be noted that loop
current will flow in the +5V supply, this must be taken
into consideration when choosing the +5V supply.
The device will operate over a very wide VBAT
supply range but care must be taken when
programming the constant current that the maximum
power dissipation is not exceeded. For the majority
External Protection Circuit
An External Protection Circuit assists in preventing
damage to the device and the subscriber equipment,
due to over-voltage conditions (see Figure 3). Also
reference MSAN-156.
2-4 Wire Conversion
The SLIC converts the balanced 2-Wire input at Tip
and Ring to a ground referenced signal at VX. The
device converts the ground referenced signal input at
VR to a balanced 2-Wire signal across Tip and Ring.
Normally the VX and VR pins connect to a Codec
that interfaces the analog signal to a digital
network.During full duplex transmission, the signal at
Tip and Ring consists of both the signal from the
2-159
MH88617
of applications this will not be a problem, however
the device could be damaged if used to drive a very
short line with the maximum battery voltage and
maximum programmable loop current.
For very long loops the constant current drive reverts
to a constant voltage source. A graph of loop current
versus line resistance is shown in Figure 4.
Under fault conditions, Tip or Ring are protected
from short circuits to ground when the current
exceeds the protection trip threshold. Under these
circumstances, the SLIC will go into a power down
mode and periodically check the line status until the
fault has been removed. Thereby minimizing power
dissipation. The SLIC will revert to an operational
state once the fault is removed.
Advance Information
The SLIC also has the ability to provide ringing on
short loops without the need for a high voltage DCRI
supply. This is achieved by connecting the DCRI pin
to a low voltage supply such as +5V or +12V
providing the subscriber equipment ringing detector
has a low enough sensitivity threshold. In this
application the input at RV needs to be a square
wave (refer MSAN-156).
The SLIC has an automatic ring-trip circuit that
ensures the ringing is removed when the subscriber
goes off-hook. However the user must still insure RC
is taken to logic 0 when SHK signals the subscriber
has gone off-hook.
Programmable Input Impedance
By connecting external passive components
between ZA and ground (AGND) the device’s input
impedance can be set to match the line impedance.
As shown in Figure 3 and Table 1. A more
comprehensive list is given in MSAN-156.
Ringing Amplification
The MH88617 incorporates an internal ringing
amplifier circuit. A balanced ringing signal is applied
across Tip and Ring, when a DC voltage is
connected to the DCRI pin, a low level sinusoidal
signal is applied to RV and RC is set to logic 1. The
ringing voltage is approximately 50 times the signal
at RV. The gain depends on the ringer load and
impedance at ZA. If an absolute gain is required, a
transistor can be fitted across ZA to give 42.
Programmable Network Balance
The network balance of the device can be
programmed by connecting external passive
components between GVX and VR, as shown in
Figure 3 and Table 1.
+5V -5V
C1
-48V 0-100V
C2
+5V
10k
SD3
SD2
SD1
SD0
VX
R1
DSTo
1.0Vrms
Sinewave
(16-68Hz)
VCC VEE
F1
TIP
E.G Teccor
P2353AB
VBAT DCRI RV
LR
RDI
MT896x
CA
F1i
CLK
DSTi
TIP
Protection
Circuit
F2
RING
MH88617
ESE
RC
VX
RING
SHK
Relay Drive
Output
Loop Current
Adjust Input
SHK
RDO
LCA
AGND
ZA
GVX
T
Z2
VR
ESI
R2
VR
Notes:
1) For Resistor and Impedance values
see Table 1
2) C1 and C2 are 100nF decoupling capacitors
3) F1 and F2 Slow Blow Fuses
Z1
1.0Vrms
Sinewave
(12/16kHz)
Figure 3 - Typical Application Circuit
2-160
Advance Information
I
LOOP
MH88617
VBAT @ -48V
LCA O/C
24mA
14mA
Constant
Current
Constant
Voltage
R
LOOP
0Ω
≈1800Ω
≈2800Ω
Figure 4 - Loop Current vs. Line Resistance
Table 1 gives table of values for some common
applications. A more comprehensive list is given in
MSAN-156.
for optimum performance forward operation is
recommended.
Meter-Pulse Injection
Programmable Transmit and Receive
Gain
The transmit gain from Tip and Ring to VX can be
programmed by connecting a resistor between GVX
and VX. Similarly the Receive Gain from VR to Tip
and Ring can be programmed by connecting an
impedance in series with VR as shown in Figure 3
and Table 1. Refer to MSAN-156 for additional
impedances.
If the External Signal Enable (ESE) is taken to logic
1 and a 12kHz or 16kHz Meter Pulse signal is
applied to the ESI pin then this signal will be
amplified and output across Tip and Ring. This is
used for calculating the cost of a telephone call.
The gain of the meter pulse signal varies with
programmed input impedance e.g. with the input
impedance programmed for 600Ω and a 200Ω AC
load applied across Tip and Ring the ESI signal will
be amplified by a factor of 2.
Some applications require the 12/16 kHz meter
pulse signal to be ramped before being input at ESI.
Off-Hook and Dial Pulse Detection
The switch hook detect output (SHK) goes to a logic
1, when loop current is above the detect threshold
(see DC Electrical Characteristics). This occurs
when the subscriber’s equipment seizes the line to
initiate a call or answer a call. When loop disconnect
dialling is being used, SHK pulses to logic 0 to
indicate the digits being dialled. This output should
be debounced by the system software.
During On-hook transmission SHK remains at logic
0.
Power Down
If AGND is applied to LCA pin the MH88617 will
enter a power down mode where the internal circuitry
is turned off and the power consumption is reduced.
This can be used to conserve power when the line is
inactive.
If the system wants to initiate a call the AGND must
be removed from the LCA before the ringing signal is
transmitted.
If the subscriber initiates a call by seizing the line, SHK
will go to logic 1. The system should monitor this and
respond by removing the AGND from LCA causing the
device to wake up.
Reversal
During normal operation i.e. LR connected to logic 1,
the DC voltage on Tip is positive with respect to
Ring. This can be reversed by applying a logic 0 to
the Line Reversal pin (LR). This feature is used for
signalling. The SLIC is functional during reversal but
2-161
Analog electronics
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