The HC5521 provides a comprehensive set of features for these applications including loop reversal, ground key detection, zero crossing ring relay operation, long loop drive and a mutually independent setting of the receive and transmit gains, and the two-wire impedance synthesis. An option is also provided for eliminating transhybrid balance on-chip. Advanced power management features combined with a small 44 lead MQFP package allow significant board space to be freed up for additional line circuits.