The 8431-21 is a general purpose clock frequency synthesizer for IA64/32 application. The VCO operates at a frequency range of 250MHz to 700MHz providing an output frequency range of 62.5MHz to 350MHz. The output frequency can be programmed using the parallel interface, M0 through M8 to the configuration logic, and the output divider control pin, DIV_SEL. Spread spectrum clocking is programmed via the control inputs SSC_CTL0 and SSC_CTL1. Programmable features of the 8431-21 support four operational modes. The four modes are spread spectrum clocking (SSC), non-spread spectrum clock and two test modes which are controlled by the SSC_CTL[1:0] pins. Unlike other synthesizers, the 8431-21 can immediately change spread-spectrum operation without having to reset the device. In SSC mode, the output clock is modulated in order to achieve a reduction in EMI. In one of the PLL bypass test modes, the PLL is disconnected as the source to the differential output allowing an external source to be connected to the TEST_I/O pin. This is useful for in-circuit testing and allows the differential output to be driven at a lower frequency throughout the system clock tree. In the other PLL bypass mode, the oscillator divider is used as the source to both the M and the Fout divide by 2. This is useful for characterizing the oscillator and internal dividers.


  • Fully integrated PLL
  • Differential 3.3V LVPECL output
  • Crystal oscillator interface
  • Output frequency range: 62.5MHz to 350MHz
  • Crystal input frequency range: 14MHz to 25MHz
  • VCO range: 250MHz to 700MHz
  • Programmable PLL loop divider for generating a variety of output frequencies
  • Spread Spectrum Clocking (SSC) fixed at 1/2% modulation for environments requiring ultra low EMI
  • PLL bypass modes supporting in-circuit testing and on-chip functional block characterization
  • Cycle-to-cycle jitter: 30ps (maximum)
  • 3.3V supply voltage
  • 0°C to 85°C ambient operating temperature
  • Replaces ICS8431-01 and ICS8431-11
  • Lead-Free package fully RoHS compliant
  • Use Replacement Part: 84314AY-02LF

Product Options

Orderable Part ID Part Status Pkg. Type Lead Count (#) Temp. Grade Pb (Lead) Free Carrier Type Buy Sample
Obsolete SOIC 28 C Yes Tube

Documentation & Downloads

Title Other Languages Type Format File Size Date
Application Notes & White Papers
AN-828 Termination - LVPECL Application Note PDF 322 KB
AN-831 The Crystal Load curve Application Note PDF 395 KB
AN-842 Thermal Considerations in Package Design and Selection Application Note PDF 495 KB
AN-803 Crystal Timing Budget and Accuracy for IDT Timing Clock Products Application Note PDF 128 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-832 Timing Budget and Accuracy Application Note PDF 131 KB
AN-834 Hot-Swap Recommendations Application Note PDF 153 KB
AN-837 Overdriving the Crystal Interface Application Note PDF 133 KB
AN-830 Quartz Crystal Drive Level Application Note PDF 143 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-802 Crystal-Measuring Oscillator Negative Resistance Application Note PDF 136 KB
AN-801 Crystal-High Drive Level Application Note PDF 202 KB
AN-806 Power Supply Noise Rejection Application Note PDF 438 KB
AN-805 Recommended Ferrite Beads Application Note PDF 121 KB
PDN# : CQ-13-01 PRODUCT DISCONTINUANCE NOTICE Product Discontinuation Notice PDF 302 KB
8431-21 IBIS Model Model - IBIS ZIP 26 KB