Description

The 8T49N282 has two independent, fractional-feedback PLLs that

can be used as jitter attenuators and frequency translators. It is

equipped with six integer and two fractional output dividers, allowing

the generation of up to eight different output frequencies, ranging

from 8kHz to 1GHz. Four of these frequencies are completely

independent of each other and the inputs. The other four are related

frequencies. The eight outputs may select among LVPECL, LVDS or

LVCMOS output levels.

This functionality makes it ideal to be used in any frequency

translation application, including 1G, 10G, 40G and 100G

Synchronous Ethernet, OTN, and SONET/SDH, including ITU-T

G.709 (2009) FEC rates. The device may also behave as a frequency

synthesizer.

The 8T49N282 accepts up to four differential or single-ended input

clocks and a crystal input. Each of the two internal PLLs can lock to

different input clocks which may be of independent frequencies. The

other two input clocks are intended for redundant backup of the

primary clocks and must be related in frequency to their primary.

The device supports hitless reference switching between input

clocks. The device monitors all input clocks for Loss of Signal (LOS),

and generates an alarm when an input clock failure is detected.

Automatic and manual hitless reference switching options are

supported. LOS behavior can be set to support gapped or un-gapped

clocks.

The 8T49N282 supports holdover for each PLL. The holdover has an

initial accuracy of ±50ppB from the point where the loss of all

applicable input reference(s) has been detected. It maintains a

historical average operating point for each PLL that may be returned

to in holdover at a limited phase slope.

The device places no constraints on input to output frequency

conversion, supporting all FEC rates, including the new revision of

ITU-T Recommendation G.709 (2009), most with 0ppm conversion

error.

Each PLL has a register-selectable loop bandwidth from 0.5Hz to

512Hz.

Each output supports individual phase delay settings to allow

output-output alignment.

The device supports Output Enable inputs and Lock, Holdover and

LOS status outputs.

The device is programmable through an I2C interface. It also supports

I

2C master capability to allow the register configuration to be read

from an external EEPROM. The user may select whether the

programming interface uses I2C protocols or SPI protocols, however

in SPI mode, read from the external EEPROM is not supported.

Features

• Supports SDH/SONET and Synchronous Ethernet clocks

including all FEC rate conversions

• Two differential outputs meet jitter limits for 100G Ethernet and

STM-256/OC-768

• <0.3ps RMS (including spurs): 12kHz to 20MHz

• All outputs <0.5ps RMS (including spurs) 12kHz to 20MHz

• Operating modes: locked to input signal, holdover and free-run

• Initial holdover accuracy of ±50ppb

• Accepts up to four LVPECL, LVDS, LVHSTL, HCSL or LVCMOS

input clocks

• Accepts frequencies ranging from 8kHz up to 875MHz

• Auto and manual input clock selection with hitless switching

• Clock input monitoring, including support for gapped clocks

• Phase-Slope Limiting and Fully Hitless Switching options to

control output phase transients

• Operates from a 10MHz to 40MHz fundamental-mode crystal

• Generates eight LVPECL / LVDS or 16 LVCMOS output clocks

• Output frequencies ranging from 8kHz up to 1.0GHz (diff)

• Output frequencies ranging from 8kHz to 250MHz (LVCMOS)

• Eight General Purpose I/O pins with optional support for status

and control

• Eight Output Enable control inputs

• Lock, Holdover and Loss-of-Signal status outputs

• Open-drain Interrupt pin

• Write-protect pin to prevent configuration registers being altered

• Programmable PLL bandwidth settings for each PLL:

• 0.5Hz, 1Hz, 2Hz, 4Hz, 8Hz, 16Hz, 32Hz, 64Hz, 128Hz, 256Hz

or 512Hz

• Optional Fast Lock function

• Programmable output phase delays in steps as small as 16ps

• Register programmable through I2C / SPI or via external I2C

EEPROM

• Bypass clock paths for system tests

• Power supply modes:

VCC / VCCA / VCCO

3.3V / 3.3V / 3.3V

3.3V / 3.3V / 2.5V

3.3V / 3.3V / 1.8V (LVCMOS)

2.5V / 2.5V / 3.3V

2.5V / 2.5V / 2.5V

2.5V / 2.5V / 1.8V (LVCMOS)

• Power down modes support consumption as low as 1.7W (see

Power Dissipation and Thermal Considerations section for

details)

• -40°C to 85°C ambient operating temperature

• Package: 72QFN, lead-free RoHs (6)