GENERAL DESCRIPTION
The AD9548 provides synchronization for many systems, including synchronous optical networks (SONET/SDH). The AD9548 generates an output clock synchronized to one of up to four differential or eight single-ended external input references. The digital PLL allows for reduction of input time jitter or phase noise associated with the external references. The AD9548 continuously generates a clean (low jitter), valid output clock even when all references have failed by means of a digitally controlled loop and holdover circuitry.
The AD9548 operates over an industrial temperature range of −40°C to +85°C.

FEATURES
   Supports Stratum 2 stability in holdover mode
   Supports reference switchover with phase build-out
   Supports hitless reference switchover
   Auto/manual holdover and reference switchover
   4 pairs of reference input pins with each pair configurable as
      a single differential input or as 2 independent single-ended inputs
   Input reference frequencies from 1 Hz to 750 MHz
   Reference validation and frequency monitoring (1 ppm)
   Programmable input reference switchover priority
   30-bit programmable input reference divider
   4 pairs of clock output pins with each pair configurable as a
      single differential LVDS/LVPECL output or as 2 single-ended CMOS outputs
   Output frequencies up to 450 MHz
   30-bit integer and 10-bit fractional programmable feedback
      divider
   Programmable digital loop filter covering loop bandwidths
      from 0.001 Hz to 100 kHz
   Optional low noise LC-VCO system clock multiplier
   Optional crystal resonator for system clock input
   On-chip EEPROM to store multiple power-up profiles
   Software controlled power-down
   88-lead LFCSP package

APPLICATIONS
   Network synchronization
   Cleanup of reference clock jitter
   GPS 1 pulse per second synchronization
   SONET/SDH clocks up to OC-192, including FEC
   Stratum 2 holdover, jitter cleanup, and phase transient
      control
   Stratum 3E and Stratum 3 reference clocks
   Wireless base station controllers
   Cable infrastructure
   Data communications