MITEL MH88617AD-PI, MH88617AT-PI, MH88617AV-PI, MH88617AS-PI Datasheet

2-157

Features

• 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

Applications

Line interface for:

• PABX/Key Telephone System

• Analog Terminal Adaptors

• Pair Gain System

• Fibre in the Loop/Wireless Local Loop

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.

Figure 1 - Functional Block Diagram

TIP

RING

GVX

VBAT VCC VEE GND LCA

Ringing Control

and

Amplifier

LR

Power

Management

Constant

Current Control

Reversal

Supervision

Auto Ring Trip

TIP / RING

Drive and

Sense

VX

VR

ZA

RDI

RDOESEESISHKDCRI

RV

RC

2 - 4 Wire

Conversion

Gain Adjust

Programmable

Impedance

Metering

Injection

Relay Driver

& Programmable
Network Balance

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

MH88617

Programmable SLIC with Ringing Amplification

Advance Information

MH88617 Advance Information

2-158

Figure 2 - Pin Connections

Pin Description

28
Pin
DIL

21
Pin
SIL

Name Description

26 1 DCRI DC Ringing V olta ge Input. A continuous DC voltage is applied to this pin. This voltage

is the positive supply rail for the internal ringing amplifier.
16 2 RDI Relay Driver Input. Relay driver control pin.
15 3 RDO Relay Driver Output. Open collector relay driver output.

54LR 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.

1 5 TIP Tip Lead. Connects to the "Tip" lead of the subscriber line.
3 6 RING Ring Lead. Connects to the "Ring" lead of the subscriber line.

12 7 VBAT Battery Voltage. Battery supply for the subscriber line. Typically -48V DC is applied to

this pin.

9 8 LCA 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 def aults the loop current

to 24mA. Setting this pin to 0V will apply power down.
28 9 VX Transmit Signal (Output). 4-wire analog signal from the SLIC.
27 10 GVX 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.
17 11 VR Receive Signal (Input). 4-wire analog signal to the SLIC.
22 12 VCC Positive Supply Voltage. +5V.
21 13 AGND Analog Ground. Ground path for the subscriber line and all DC power supplies,

normally connected to system ground.
20 14 VEE Negative Supply Voltage. -5V.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

DCRI

RDI

RDO

LR

TIP
RING
VBAT

LCA

VX

GVX

VR

VCC

AGND

VEE

RV

ESE

ESI

IC

SHK

RC

ZA

21 Pin SIL

28 Pin DIL

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

TIP

IC

RING

IC

LR

RC

ESE

ESI

LCA

IC
IC

VBAT

IC

SHK

VX
GVX
DCRI
IC

IC
IC

VCC
AGND
VEE

RDO

RDI

VR

RV

ZA

Advance Information MH88617

2-159

18 15 RV 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.
7 16 ESE External Signal Enable. Meter pulse input enable.
8 17 ESI External Signal Input. Meter pulse input.

2,

4,10

11,13

,23

25,24

18 IC Internal Connection. No connection should be made to this pin.

14 19 SHK Switch Hook Detect (Output). A logic 1 at this pin indicates when the subscriber has

gone Off-Hook.
620RCRinging Control (Input). A logic 1 will cause the ringing voltage to be applied to the line.

19 21 ZA Line Impedance. Connect passive components from ZA to ground to match input and

line impedance.

Pin Description (continued)

28
Pin
DIL

21
Pin
SIL

Name Description

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.

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

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 on­hook. This can be used when sending caller line
identification information.

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 major ity

MH88617 Advance Information

2-160

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.

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.

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.

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.

Figure 3 - Typical Application Circuit

TIP

RING

VX

VR

AGND

VCC

TIP

RING

+5V

MH88617

Protection

Circuit

Notes:

ZA

Z1

VEE VBAT DCRI

-5V

-48V

RV

LR

GVX

SD3
SD2

SD1
SD0

RDI

ESE

RC

VX

VR

MT896x

ESI

SHK

RDO

SHK

Relay Drive
Output

LCA

Loop Current

Adjust Input

1.0Vrms
Sinewave
(16-68Hz)

1.0Vrms
Sinewave
(12/16kHz)

1) For Resistor and Impedance values

0-100V

DSTo

DSTi

CLK

F1i

CA

+5V

10k

C1 C2

2) C1 and C2 are 100nF decoupling capacitors

R2

Z2

R1

see Table 1

T

E.G Teccor

P2353AB

F1

F2

3) F1 and F2 Slow Blow Fuses

Advance Information MH88617

2-161

Table 1 gives table of values for some common
applications. A more comprehensive list is given in
MSAN-156.

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.

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.

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

for optimum performance forward operation is
recommended.

Meter-Pulse Injection

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.

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.

Figure 4 - Loop Current vs. Line Resistance

24mA

0Ω

≈1800Ω

R

LOOP

I

LOOP

VBAT @ -48V
LCA O/C

Constant

Current

Constant

Voltage

≈2800Ω

14mA