Le79228
Data Sheet
PRODUCT DESCRIPTION
The VE790 series voice chip sets integrate all functions of the subscriber line for four subscriber lines. One or more of two chip
types are used to implement the line card; a VE790 series ISLIC device and a Le79228 Quad ISLAC device. These provide the
following basic functions:
1. The VE790 series ISLIC device: A high voltage, bipolar IC that drives the subscriber line, maintains longitudinal balance and
senses line conditions.
2. The Le79228 Quad ISLAC device: A low voltage CMOS IC that provides conversion and DSP functions for all four channels.
Complete schematics of line cards using the Le79228 Quad ISLAC device for internal and external ringing are shown in
Application Circuits, on page 28.
The VE790 series ISLIC device uses reliable, bipolar technology to provide the power necessary to drive a wide variety of
subscriber lines. It can be programmed by the Quad ISLAC device to operate in eight different modes that control power
consumption and signaling. This enables it to have full control over the subscriber loop. The VE790 series ISLIC device is
designed to be used exclusively with the Le79228 Quad ISLAC device as part of a multiple-line chip set.
The VE790 series ISLIC device implements a linear loop-current feeding method with the enhancement of intelligent thermal
management in a controlled manner. This limits the amount of power dissipated on the VE790 series ISLIC chip by dissipating
excess power in external resistors.
Each Le79228 Quad ISLAC device contains high-performance analog circuits that provide A/D and D/A conversion for voice
(codec/filter), DC-feed and supervision signals for four subscriber channels. The Le79228 Quad ISLAC device contains a DSP
core that handles signaling, DC-feed, supervision and line diagnostics for all four channels.
The DSP core selectively interfaces with three types of backplanes:
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Standard PCM/MPI
Standard GCI
Modified GCI with a single analog line per GCI channel
The Le79228 Quad ISLAC device provides a complete software configurable solution to the BORSCHT functions as well as
complete programmable control over subscriber line DC-feed characteristics, such as current limit and feed resistance. In
addition, these chip sets provide system level solutions for the loop supervisory functions and metering. In total, they provide a
programmable solution that can satisfy worldwide line card requirements by software configuration.
Software programmed filter coefficients, DC-feed data and supervision data are easily calculated with the WinSLAC software.
This PC software is provided free of charge and allows the designer to enter a description of system requirements. WinSLAC
then computes the necessary coefficients and plots the predicted system results.
The VE790 series ISLIC device interface unit inside the Le79228 Quad ISLAC device processes information regarding the line
voltages, loop currents and battery voltage levels. These inputs allow the Le79228 Quad ISLAC device to place several key
VE790 series ISLIC device performance parameters under software control.
The main functions that can be observed and/or controlled through the Le79228 Quad ISLAC device backplane interface are:
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DC-feed characteristics
Ground-key detection
Off-hook detection
Metering signal
Longitudinal operating point
Subscriber line voltage and currents
Ring-trip detection
Abrupt and smooth reversal
Subscriber line matching
Ringing generation
Sophisticated line and circuit tests
To accomplish these functions, the VE790 series ISLIC device collects the following information and feeds it, in analog form, to
the Le79228 Quad ISLAC device:
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The metallic (IMT) and longitudinal (ILG) loop currents
The AC (VTX) and DC (VSAB) loop voltages
The outputs supplied by the Le79228 Quad ISLAC device to the VE790 series ISLIC device are then:
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A voltage (VHLi*) that provides control for the following high-level VE790 series ISLIC device outputs:
DC loop current
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Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
