Description
This electronic subscriber loop interface circuit (SLIC) is optimized for low-power consumption while providing an extensive set of features.
Quiet polarity reversal is possible because the ac path is uninterrupted during transition.
The L7554 includes the ground start state and a summing node for meter pulse injection to 2.2 Vrms. A spare, uncommitted op amp is included for meter pulse filtering.

FEATUREs
■ Low active power (typical 165 mW during on-hook transmission)
■ Sleep state for low idle power (76 mW)
■ Quiet Tip/Ring polarity reversal
■ Supports meter pulse injection
■ Spare op amp for meter pulse filtering
■ –24 V to –72 V power supply operation
■ Distortion-free on-hook transmission
■ Convenient operating states:
   — Forward powerup
   — Polarity reversal powerup
   — Forward low-power scan
   — Polarity reversal low-power scan
   — Ground start
   — Disconnect (high impedance)
■ Adjustable supervision functions:
   — Off-hook detector with longitudinal rejection
   — Ground key detector
   — Ring trip detector
■ Independent, adjustable, dc and ac parameters:
   — dc feed resistance
   — Loop current limit
   — Termination impedance
■ Thermal protection