The HC-5524 telephone Subscriber Line Interface Circuit
integrates most of the BORSCHT functions on a monolithic
IC. The device is manufactured in a Dielectric Isolation (DI)
process and is designed for use as a 24V interface between
the traditional telephone subscriber pair (Tip and Ring) and
the low voltage filtering and coding/decoding functions of the
line card. Together with a secondary protection diode bridge,
the device will withstand 500V induced surges, in plastic
packages. The SLIC also maintains specified transmission
performance in the presence of externally induced
longitudinal currents. The BORSCHT functions that the SLIC
provides are:
? Battery Feed with Subscriber Loop Current Limiting
? Overvoltage Protection
? Ring Relay Driver
? Supervisory Signaling Functions
? Hybrid Functions (with External Op-Amp)
? Test (or Battery Reversal) Relay Driver
In addition, the SLIC provides selective denial of power to
subscriber loops, a programmable subscriber loop current
limit from 20mA to 60mA, a thermal shutdown with an alarm
output and line fault protection. Switch hook detection, ring
trip detection and ground key detection functions are also
incorporated in the SLIC device.
The HC-5524 SLIC is ideally suited for line card designs in
PBX and DLC systems, replacing traditional transformer
solutions.