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851021 - Block Diagram
851021 - Pinout


1-to-21,Differential HCSL Fanout Buffer

The 851021 is a 1-to-21 Differential HCSL Fanout Buffer. The 851021 is designed to translate any differential signal levels to differential HCSL output levels. An external reference resistor is used to set the value of the current supplied to an external load/termination resistor. The load resistor value is chosen to equal the value of the characteristic line impedance of 50 ohms. The 851021 is characterized at an operating supply voltage of 3.3V. The differential HCSL outputs, accurate crossover voltage and duty cycle make the 851021 ideal for interfacing to PCI Express® and FBDIMM applications.


  • Twenty-one differential HCSL outputs
  • Translates any differential input signal (LVPECL, LVHSTL, LVDS, HCSL) to HCSL levels without external bias networks
  • Maximum output frequency: 250MHz
  • Output skew: 395ps (maximum)
  • Part-to-part skew: 335ps (maximum)
  • Output drift: 140ps (maximum)
  • VOH: 850mV (maximum)
  • Full 3.3V supply voltage
  • Available in lead-free (RoHS 6) packages
  • 0°C to 70°C ambient operating temperature

Product Specification

Outputs (#)Output TypeOutput Freq Range (MHz)Input Freq (MHz)Inputs (#)Input TypeOutput Banks (#)Core Voltage (V)Output Voltage (V)Divider ValueOutput Skew (ps)Additive Phase Jitter Typ RMS (ps)
21HCSL0.000000 - 250.0000000.000000 - 250.0000001LVDS, HSTL, LVPECL, HCSL13.33.33950.2

Product Options

Orderable Part IDPart StatusPkg. CodePkg. TypeLead Count (#)Temp. GradePb (Lead) FreeCarrier TypeSample & Buy
851021AYLFActiveEDG64P2TQFP64CYesTrayCheck Availability
851021AYLFTActiveEDG64P2TQFP64CYesReelCheck Availability


Technical Documentation

Title Other Languages Type Format File Size Datesort icon
Datasheets & Errata
851021 Datasheet Datasheet PDF 296 KB Nov 10, 2015
Apps Notes & White Papers
AN-828 Termination - LVPECL Application Note PDF 229 KB Jul 5, 2016
AN-843 PCI Express Reference Clock Requirements Application Note PDF 1.81 MB May 13, 2014
AN-844 Termination - AC Coupling Clock Receivers Application Note PDF 82 KB May 13, 2014
show all (12)
AN-842 Thermal Considerations in Package Design and Selection Application Note PDF 403 KB May 12, 2014
AN-840 Jitter Specifications for Timing Signals Application Note PDF 349 KB May 8, 2014
AN-835 Differential Input with VCMR being VIH Referenced Application Note PDF 77 KB May 6, 2014
AN-836 Differential Input to Accept Single-ended Levels Application Note PDF 37 KB May 6, 2014
AN-833 Differential Input Self Oscillation Prevention Application Note PDF 94 KB May 6, 2014
AN-834 Hot-Swap Recommendations Application Note PDF 67 KB May 6, 2014
AN-827 Application Relevance of Clock Jitter Application Note PDF 1.06 MB Apr 24, 2014
AN-815 Understanding Jitter Units Application Note PDF 476 KB Apr 24, 2014
AN-805 Recommended Ferrite Beads Application Note PDF 38 KB Jan 15, 2014
PCN# : A1606-02 Add Greatek Taiwan as Alternate Assembly Product Change Notice PDF 567 KB Aug 26, 2016
PCN# : A1402-02 Alternate Assembly Locations Product Change Notice PDF 34 KB Sep 28, 2014
PCN# : TB1405-01 New Carrier Tape and Quantity per Reel Product Change Notice PDF 788 KB Jul 7, 2014
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 25, 2016
IDT Fanout Buffers Product Overview Product Brief PDF 739 KB Feb 17, 2015
show all (4)
High-Performance, Low-Phase Noise Clocks Buffers product brief Product Brief PDF 378 KB Aug 14, 2012

Software & Tools

Title Type Format File Size Datesort icon
851021 IBIS Model_RREF_475 Model - IBIS ZIP 8 KB Jan 3, 2007

News & Additional Resources

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