The Zarlink MT91600 provides an interface between a switching system and a subscriber loop, mainly for short loop SLIC applications. The functions provided by the MT91600 include battery feed, programmable constant current, 2 W to 4 W conversion, off-hook and dial pulse detection, user definable line and network balance impedance's and the capability of programming the audio gain externally. The device is fabricated as a CMOS circuit in a 28 pin SSOP package.