The HC-5509B 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 functions 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: