I2C Programmable Ethernet Clock Generator

The 8T49N4811 is a highly flexible FemtoClock® NG pin-programmable clock generator suitable for networking and communications applications. It is able to generate five different output frequencies with multiple copies of each. A fundamental mode crystal, single-ended, or differential input reference may be used as the source for the output frequency.
The use of pin-programming to select the input source / frequency, desired output frequencies and output styles allow a single device to be used in a wide variety of applications without the need for register programming.
Selection pins use 3-level options to maximize flexibility while minimizing package size. Selection is performed by tying a selection pin high or low or by leaving it floating, eliminating the need for passive components to drive a desired logic level.


  • Fourth generation FemtoClock® NG technology
  • Generates multiple copies of 25MHz, 50MHz, 100MHz, 125MHz, 156.25MHz or 312.5MHz
  • Typical input frequency is 25MHz, with optional 125MHz and 156.25MHz input support
  • Differential outputs are pin programmable for LVDS or LVPECL
  • RMS phase jitter at 156.25MHz: <300fs typical
  • Power Supply Rejection Ratio better than -50dBc from 10k-1.5MHz at 3.3V power supply
  • Full 3.3V and 2.5V Supply Voltages
  • -40°C to +85°C ambient operating temperature
  • 56-pin VFQFPN, lead-free (RoHS 6) packaging

Product Options

Orderable Part ID Part Status Pkg. Code Pkg. Type Lead Count (#) Temp. Grade Pb (Lead) Free Carrier Type Buy Sample
8T49N4811NLGI Active NLG56P4 VFQFPN 56 I Yes Tray Availability
8T49N4811NLGI8 Active NLG56P4 VFQFPN 56 I Yes Reel Availability

Technical Documentation

Title Other Languages Type Format File Size Date
Datasheets & Errata
8T49N4811 Final Data Sheet Datasheet PDF 545 KB Nov 19, 2015
Application Notes & White Papers
AN-828 Termination - LVPECL Application Note PDF 229 KB Jul 5, 2016
AN-845 Termination - LVCMOS Application Note PDF 62 KB May 12, 2014
AN-844 Termination - AC Coupling Clock Receivers Application Note PDF 82 KB May 12, 2014
AN-842 Thermal Considerations in Package Design and Selection Application Note PDF 403 KB May 11, 2014
AN-835 Differential Input with VCMR being VIH Referenced Application Note PDF 77 KB May 10, 2014
AN-840 Jitter Specifications for Timing Signals Application Note PDF 349 KB May 7, 2014
AN-834 Hot-Swap Recommendations Application Note PDF 67 KB May 5, 2014
AN-836 Differential Input to Accept Single-ended Levels Application Note PDF 37 KB May 5, 2014
AN-827 Application Relevance of Clock Jitter Application Note PDF 1.06 MB Apr 23, 2014
AN-815 Understanding Jitter Units Application Note PDF 476 KB Apr 23, 2014
AN-805 Recommended Ferrite Beads Application Note PDF 38 KB Jan 14, 2014
PCN# : A1611-02 Add JCET China as Alternate Assembly and Change of Material Set at Alternate Assembly Location Product Change Notice PDF 583 KB Dec 19, 2016
Timing Solutions Products Overview Overview PDF 964 KB Sep 19, 2018
IDT Products for Radio Applications 日本語 Product Brief PDF 2.34 MB Nov 29, 2016
IDT Clock Generation Overview 日本語 Overview PDF 1.83 MB Apr 28, 2016
IDT Clock Distribution Overview 日本語 Overview PDF 3.79 MB Apr 24, 2016