The PBL 386 21/2 Subscriber Line Interface Circuit (SLIC) is a 90 V bipolar integrated circuit for use in DAML, FITL and other telecommunications equipment. The PBL 386 21/2 has been optimized for low total line interface cost and a high degree of flexibility in different applications. The PBL 386 21/2 has constant current feed, programmable to max. 30 mA. A second lower battery voltage may be connected to the device to reduce short loop power dissipation. The SLIC automatically switches between the two battery supply voltages without need for external components or external control. The SLIC incorporates loop current, ground key and ring trip detection functions. The PBL 386 21/2 is compatible with loop start signaling. Two- to four-wire and four- to two-wire voice frequency (VF) signal conversion is accomplished by the SLIC in conjunction with either a conventional CODEC/filter or with a programmable CODEC/filter, e.g. SLAC, SiCoFi, Combo II. The programmable the two-wire impedance, complex or real, is set by a simple external network. Longitudinal voltages are suppressed by a feedback loop in the SLIC and the longitudinal balance specifications meet Bellcore TR909 requirements. The PBL 386 21/2 package options are 24-pin SSOP, 24-pin SOIC or 28-pin PLCC.