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