8T49N241 Datasheet, PDF (1/64 Pages) Integrated Circuit Systems – Manual clock selection control input

FemtoClock^®NG Universal Frequency
Translator
8T49N241
DATA SHEET
General Description
The 8T49N241 has one fractional-feedback PLL that can be used as
a jitter attenuator and frequency translator. It is equipped with one
integer and three fractional output dividers, allowing the generation of
up to four different output frequencies, ranging from 8kHz to 1GHz.
These frequencies are completely independent of each other, the
input reference frequencies and the crystal reference frequency. The
device places virtually 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. The outputs may select among LVPECL, LVDS, HCSL or
LVCMOS output levels.
This makes it ideal to be used in any frequency synthesis application,
including 1G, 10G, 40G and 100G Synchronous Ethernet, OTN, and
SONET/SDH, including ITU-T G.709 (2009) FEC rates.
The 8T49N241 accepts up to two differential or single-ended input
clocks and a fundamental-mode crystal input. The internal PLL can
lock to either of the input reference clocks or just to the crystal to
behave as a frequency synthesizer. The PLL can use the second
input for redundant backup of the primary input reference, but in this
case, both input clock references must be related in frequency.
The device supports hitless reference switching between input
clocks. The device monitors both 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 8T49N241 supports holdover. 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 the PLL that may be returned to in
holdover at a limited phase slope.
The PLL has a register-selectable loop bandwidth from 0.2Hz to
6.4kHz.
The device supports Output Enable & Clock Select inputs and Lock,
Holdover & LOS status outputs.
The device is programmable through an I²C interface. It also
supports I²C master capability to allow the register configuration to
be read from an external EEPROM.
Programming with IDT’s Timing Commander software is
recommended for optimal device performance. Factory
pre-programmed devices are also available.
Applications
• OTN or SONET / SDH equipment
• Gigabit and Terabit IP switches / routers including Synchronous
Ethernet
• Video broadcast
Features
• Supports SDH/SONET and Synchronous Ethernet clocks including
all FEC rate conversions
• 0.35ps RMS Typical Jitter (including spurs): 12kHz to 20MHz
• Operating Modes: Synthesizer, Jitter Attenuator
• Operates from a 10MHz to 50MHz fundamental-mode crystal
• Initial holdover accuracy of +50ppb.
• Accepts up to 2 LVPECL, LVDS, LVHSTL or LVCMOS input clocks
• Accepts frequencies ranging from 8kHz to 875MHz
• Auto and manual clock selection with hitless switching
• Clock input monitoring including support for gapped clocks
• Phase-slope limiting and fully hitless switching options to control
output clock phase transients
• Generates four LVPECL / LVDS / HCSL or eight LVCMOS output
clocks
• Output frequencies ranging from 8kHz up to 1.0GHz
(differential)
• Output frequencies ranging from 8kHz to 250MHz (LVCMOS)
• One integer divider ranging from ÷4 to ÷786,420
• Three fractional output dividers (see Section, “Output Dividers”)
• Programmable loop bandwidth settings from 0.2Hz to 6.4kHz
• Optional fast-lock function
• Four General Purpose I/O pins with optional support for status &
control:
• Two Output Enable control inputs provide control over the four
clocks
• Manual clock selection control input
• Lock, Holdover and Loss-of-Signal alarm outputs
• Open-drain Interrupt pin
• Register programmable through I²C or via external I²C EEPROM
• Full 2.5V or 3.3V supply modes, 1.8V support for LVCMOS outputs,
GPIO and control pins
• -40°C to 85°C ambient operating temperature
• Package: 40QFN, lead-free (RoHS 6)
8T49N241 REVISION 1 08/07/15
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