The 844S42I is a 3.3V compatible, PLL based clock synthesizer targeted for clock generation in high-performance instrumentation, networking and computing applications. Using either the serial (I2C) or parallel programming interface, the 844S42I enables the generation of clock frequencies in the range of 81MHz to 2592MHz. The internal crystal oscillator uses the external quartz crystal as the basis of its frequency reference. Alternatively, a LVCMOS compatible clock signal can be used as PLL reference signal. The devices uses an integer-N synthesizer architecture and is optimized for low-jitter generation. The VCO within the PLL operates over a range of 1296MHz to 2592MHz. Its output is scaled by a divider that is configured by either the I2C or parallel interfaces. The crystal oscillator frequency fXTAL, the PLL pre-divider P, the feedback-divider M and the PLL post-divider N determine the output frequency. The feedback path of the PLL is internal. The PLL post-dividers NA and NB are configured through either the I2C or the parallel interfaces, each can provide one of seven division ratios (1, 2, 3, 4, 6, 8, 16). This divider extends the performance of the part while providing a typical 50% duty cycle. The high-frequency outputs QA and QB are differential and are capable of driving a pair of transmission lines. The positive supply voltage for the internal PLL is separated from the power supply for the core logic and output drivers to minimize noise induced jitter. The serial interface is I2C compatible and provides read and write access to the internal PLL configuration registers. The lock state of the PLL is indicated by the LVCMOS-compatible LOCK_DT output. This device provides a clock enable control input that, when active (LOW), allows the outputs to switch normally, and when inactive (HIGH), places the outputs in a high impedance state. The 844S42I is packaged in a 8mm x 8mm 56-lead VFQFN package.


  • Programmable frequency synthesis optimized for instrumentation, networking and computing applications
  • 81MHz to 2592MHz synthesized clock output signal
  • Two differential, universal LVDS or LVPECL compatible high-frequency outputs
  • Output frequency programmable through 2-wire I2C bus or parallel interface
  • On-chip crystal oscillator for reference frequency generation
  • Alternative LVCMOS/LVTTL compatible reference clock input
  • Clock stop and output enable functionality
  • PLL lock indicator output (LVCMOS/LVTTL)
  • LVCMOS/LVTTL compatible control inputs
  • Fully integrated PLL
  • SiGe Technology
  • Full 3.3V supply voltage
  • -40°C to 85°C ambient operating temperature
  • Available in a lead-free (RoHS 6) compliant package

Product Options

Part Number Part Status Pkg. Type Lead Count (#) Temp. Grade Pb (Lead) Free Carrier Type Buy Sample
Active VFQFPN 56 I Yes Tray
Active VFQFPN 56 I Yes Reel

Documentation & Downloads

Title language Type Format File Size Date
Datasheets & Errata
ICS844S42I Datasheet Datasheet PDF 597 KB
Application Notes & White Papers
AN-828 Termination - LVPECL Application Note PDF 322 KB
AN-846 Termination - LVDS Application Note PDF 133 KB
AN-844 Termination - AC Coupling Clock Receivers Application Note PDF 170 KB
AN-842 Thermal Considerations in Package Design and Selection Application Note PDF 495 KB
AN-840 Jitter Specifications for Timing Signals Application Note PDF 442 KB
AN-838 Peak-to-Peak Jitter Calculations Application Note PDF 115 KB
AN-839 RMS Phase Jitter Application Note PDF 233 KB
AN-836 Differential Input to Accept Single-ended Levels Application Note PDF 120 KB
AN-835 Differential Input with VCMR being VIH Referenced Application Note PDF 160 KB
AN-827 Application Relevance of Clock Jitter Application Note PDF 1.15 MB
AN-815 Understanding Jitter Units Application Note PDF 565 KB
AN-805 Recommended Ferrite Beads Application Note PDF 121 KB
PCN# : A1904-01 Add Greatek, Taiwan as an Alternate Assembly Facility Product Change Notice PDF 983 KB
PCN# : A1807-01 Gold wire to Copper Wire Product Change Notice PDF 32 KB
PCN# : TB1504-01R1 Qty per Reel Standardization for Selective Packages Product Change Notice PDF 95 KB
PCN# : TB1504-01 Qty per Reel Standardization for Selective Packages Product Change Notice PDF 50 KB
844S42I IBIS Model Model - IBIS ZIP 98 KB
RF Timing Family Product Overview Overview PDF 331 KB
IDT Clock Generation Overview 日本語 Overview PDF 1.83 MB