8440258AKI-45LF

Specialized ICS Overview

The Renesas Electronics ICS8440258AKI-45 is an eight-output FemtoClock frequency synthesizer designed for Gigabit and 10 Gigabit Ethernet clock generation. It utilizes a 25MHz parallel resonant crystal to produce 156.25MHz and 125MHz clocks with mixed LVDS and LVCMOS/LVTTL outputs. The device employs third-generation low phase noise VCO technology, achieving typical RMS phase jitter of 0.41ps at 125MHz and 0.43ps at 156.25MHz. Operating on a single 2.5V supply, it supports selectable crystal or reference clock inputs via a dedicated control pin.

Specialized ICS Feature Summary

• Eight outputs: one differential LVDS (156.25MHz/125MHz), four differential LVDS (125MHz), and three single-ended LVCMOS/LVTTL (125MHz).
• Ultra-low phase noise performance with typical RMS jitter of 0.41ps at 125MHz and 0.43ps at 156.25MHz.
• Flexible input configuration selectable via F_SEL and nPLL_BYPASS pins for crystal oscillator or single-ended reference clock.
• Compact 32-lead VFQFN package (5mm x 5mm) optimized for space-constrained applications.

Specialized ICS Applications

• Gigabit Ethernet systems
• 10 Gigabit Ethernet systems

Specialized ICS Procurement Notes

Verify the manufacturer origin, as the datasheet identifies Integrated Device Technology (IDT) as the original producer. Confirm that the 'LF' suffix indicates lead-free compliance and RoHS 6 adherence. Ensure the specific ordering suffix matches the required shipping packaging format, such as tray or tape and reel.

Specialized ICS Selection Notes

Select this component when low jitter is critical for Ethernet synchronization. Ensure the design accommodates a 25MHz 18pF parallel resonant crystal if using the internal oscillator. Verify power supply isolation requirements to maintain specified jitter performance, as separate supplies are provided for core, LVDS, and LVCMOS sections.

Specialized ICS Part Context

This part belongs to the FemtoClock family of specialized ICs. Originally manufactured by IDT before its acquisition by Renesas Electronics, it serves as a high-performance clock generator. The device is distinct from general-purpose oscillators due to its programmable output divider and mixed-signal interface capabilities.

Specialized ICS Replacement Considerations

Direct replacement requires matching the 32-VFQFPN package and electrical specifications. Verify compatibility with existing PCB layout, particularly regarding thermal vias for the exposed pad and power supply decoupling to ensure signal integrity is maintained.

Specialized ICS FAQ

What is the maximum operating temperature?

The device operates within an ambient temperature range of -40°C to +85°C.

How is the PLL bypass function controlled?

The nPLL_BYPASS pin controls the mode; a logic low enables the PLL with the crystal input, while a logic high bypasses the PLL to use the REF_CLK input.

Can the XTAL_IN pin accept an external clock signal?

Yes, the XTAL_IN pin can be overdriven by an LVCMOS or differential driver through an AC coupling capacitor, allowing it to function as a reference clock input.