Obsolescence Notice
This product is obsolete.
This information is available for your
convenience only.
For more information on
Zarlink’s obsolete products and
replacement product lists, please visit
http://products.zarlink.com/obsolete_products/
MH88615
Standard SLIC with Ringing Amplification
Preliminary Information
Features
•
•
•
•
•
•
•
•
•
•
•
2W to 4W conversion
Battery Feed to line
Off-Hook and dial pulse detection
Power Denial
Integral Ringing Amplifier
Programmable Loop Current
Wide Battery Voltage Operating Range
Variants
- 1 Germany/Spain/South Africa/Australia
- 3 UK
- 7 North America
DS5242
ISSUE 8
October 2001
Ordering Information
MH88615AT-3/-7
20 Pin 90° Package
MH88615T-1/3/7
20 Pin 90° Package
0°C to 70°C
Description
The Zarlink MH88615 SLIC provides an interface
between a switching system and a subscriber loop.
The functions provided by the MH88615 include
battery feed, ringing amplification, 2W to 4W
conversion, current feed, off-hook detection and dial
pulse detection. The device is fabricated as a thick
film hybrid.
Applications
Line Interface for:
• PABX
• Pair Gain Systems
• Satellite Communication Systems
• Key Telephone Systems
• Terminal Adapters
• Cordless Local Loop
PD
VBAT
DCRI
RV
Power Denial
Ringing Control
RC
VR
TIP
Tip and
Ring
RING
Drivers
2 To 4-Wire
Conversion
VX
VREF
Loop
Constant
Current Feed
Supervision
SHK
CAP
Figure 1 - Block Diagram
2-1
MH88615
TIP
RING
IC
DCRI
LPGND
VBAT
IC
VDD
AGND
VEE
RC
PD
IC
SHK
VR
VREF
CAP
VX
IC
RV
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
90° Version
Preliminary Information
Figure 2 - Pin Connections
Pin Description
Pin#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Name
TIP
RING
IC
DCRI
LPGND
VBAT
IC
VDD
AGND
VEE
RC
PD
IC
SHK
VR
VREF
Description
Tip Lead.
Connects to the "Tip" or "A" lead of subscriber line.
Ring Lead.
Connects to the "Ring" or "B" lead of subscriber line.
Internal Connection.
This pin is internally connected and must be left open circuit.
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.
Battery Ground.
V
BAT
return path for subscriber line. Connects to the system energy
dumping ground. LPGND and AGND must be connected together within the system.
Battery Voltage.
Battery supply feed for subscriber line. Typically -48V DC is applied
to this pin.
Internal
Connection.
This pin is internally connected and must be left open circuit.
Positive Supply Voltage.
+5V DC supply rail. VDD must not be applied before VEE is
applied.
Analogue Ground.
V
DD
and V
EE
return path. AGND and LPGND must be connected
together within the system.
Negative Supply Voltage.
-5V DC supply rail. VDD must not be applied before VEE is
applied.
Ringing Control.
A logic 1 enables a balanced ringing voltage to be applied to the
subscriber line when the correct Ringing Voltage input is applied.
Power Denial.
A logic 1 will isolate the battery voltage from Tip and Ring.
Internal Connection.
This pin is internally connected and must be left open circuit.
Switch Hook Detect.
A logic 1 indicates when the subscriber line has gone off-hook.
Receive Signal (input).
This is the analogue signal to the subscriber’s set.
Reference Voltage.
A DC reference voltage is applied to this pin to set the constant
current feed to subscriber line. This pin may also be grounded for normal 25mA loop
current when V
BAT
= -48V.
2-2
Preliminary Information
Pin Description
Pin#
17
Name
CAP
Description
MH88615
Ring Trip Filter Capacitor.
A capacitor should be connected from this pin to ground
whilst ringing is applied. This filters out low frequency ringing signals preventing false
off-hook conditions.
Transmit Signal (output).
This is the analogue signal from the subscriber’s set.
Internal Connection.
This pin is internally connected and must be left open circuit.
Ringing Voltage. A low level AC sinusoid is applied as the ringing signal at this pin.
This signal is amplified and applied to the subscriber line. A source with less than 10Ω
output impedance should be used to supply this signal.
No Connection.
These pins are provided for mechanical mounting only on the surface
mount versions.
Not Fitted.
No pins are fitted in these positions.
or their local Zarlink Sales Office, Distributor or
Representative.
18
19
20
VX
IC
RV
21, 22,
39, 40
23 - 38
NC
Functional Description
The Zarlink MH88615 standard SLIC provides an
interface between a switching system and a
subscriber loop. The functions provided by the
MH88615 include battery feed, integral ringing
amplifier, 2W to 4W conversion, constant current
feed, off-hook detection and dial pulse detection.
The device is fabricated as a thick film hybrid in a 20
pin package format for 90° versions.
The MH88615 is intended for applications where low
cost and a basic functionality are important. The
MH88615 features an integral ringing amplifier which
enables a system designer to provide ringing without
having to generate a high voltage, high current AC
signal.
The SLIC implements a 2-4 wire converter which is
usually connected to a CODEC. This provides an
interface from the 2 wire subscriber loop to a TDM
(time division multiplex), PCM (pulse code
modulation) digital link.
Powering of the subscriber line is provided through
precision battery feed resistors on the circuit. The
thick film hybrid circuit also contains control,
signalling and status circuits which combine to
provide a comprehensive line interface solution. A
power denial facility is provided which isolates the
battery feed from the Tip and Ring leads. This can
remove a line from service which will reduce power
consumption.
An Application Note MSAN-151 is available to
provide technical assistance to the customer in their
use of the MH88615 product. The customer can
obtain a copy of the Applications Note from the web
DC Current Limit
Under normal Ring ground or Tip ground conditions
the current is limited to 45mA. Both leads should not
be simultaneously grounded.
Ringing and Ring Trip Detection
The MH88615 incorporates an integral ringing
amplifier. When a logic 1 is applied to the Ringing
Control (RC) pin a balanced ringing signal equal to
60x the AC sine wave applied to the RV pin is placed
on the unloaded Tip and Ring leads. See
Recommended Operating Conditions for details of
the AC ringing generator voltages.
The internal off-hook detection circuit monitors
changing DC levels on Tip and Ring and indicates an
off-hook condition by taking SHK pin to logic 1.
Whilst ringing is being applied there is a large AC
component present on the line which must be filtered
at the input to the detection circuit for it to operate
properly. The Application Circuit (Figure 3) shows
how this is achieved. Since C1 will remove dial pulse
signals from the line it must be isolated during pulse
dialing and resistor R1 is switched in using a sense
drive output (SD3) on a Zarlink MT896x CODEC.
Applications which solely use DTMF signalling can
have C1 permanently connected to ground. More
details, including an entirely hardware solution for
Ringing Voltage Filtering, are available in MSAN-
151.
2-3
MH88615
When a subscriber set goes off-hook during ringing
(RC is logic 1) the SHK pin will go to a logic 1 within
200ms. Ringing is not automatically removed from
the line. Systems should be designed such that the
RC pin of the hybrid is taken to logic 0 within 200ms
of SHK going to logic 1. The system must also
ensure that the RC pin will not go to logic 1 again
within 400ms of SHK going to logic 1. These two
functions can be realized using a software or a
hardware solution. A suitable circuit to perform both
of these functions is given in MSAN-151.
Preliminary Information
Input and Network Balance Impedances
Variants are available to meet different country line
impedances, they are as follows:
MH88615T-1
Africa, Australia
Zin = 220Ω+(820Ω//115nF)
Znet = 220Ω+(820Ω//115nF)
MH88615T-3
UK
Power Denial
A logic 1 applied to the power denial input removes
the battery voltage from the loop driver circuitry. The
resulting loop current is negligible and power
consumption is minimized. The power denial function
is useful for disabling a loop which may have a fault.
Note that the SHK is invalid during power denial.
Zin = 300Ω+(1000Ω//220nF)
Znet = 370Ω+(620Ω//310nF)
MH88615T-7
North America
Constant Current Feed
The loop current is programmed by the DC reference
voltage applied to V
REF.
The loop current is given by
the formula:
IIoop = -(0.52V
BAT
+ 4.24V
REF
)mA
Zin = 600Ω
Znet = 350Ω+(1kΩ//210nF)
Switch Hook Detection
When the DC current exceeds an internal threshold
level which represents a loop current level of
typically 10mA, the switch hook output (SHK) will
switch to a logic 1. If the loop resistance is so high
that V
BAT
can no longer supply the required loop
current, the output SHK will switch to logic 0.
Transmit Gain
Transmit gain (Tip-Ring to VX) is fixed at 0dB. For
correct gain, the SLIC input impedance must match
the line impedance.
Receive Gain
Receive Gain (VR to Tip-Ring) is fixed at 0dB. For
correct gain, the SLIC input impedance must match
the line impedance.
2-4
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