HC-5509A1 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 high voltage interface between the traditional telephone subscriber pair (Tip and Ring) and the low voltage filtering and coding/decoding func- tions of the line card. Together with a secondary protection diode bridge and “feed” resistors, the device will withstand 1000V lightning 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 20 to 60mA, a thermal shutdown with an alarm out- put and line fault protection. Switch hook detection, ring trip detection and ground key detection functions ar
