8T49N222B-110NLGI8 Guide: The 156.25MHz FemtoClock Translator

In high-speed networking, timing is everything. A "jittery" clock signal can cause bit errors that bring a 10GbE link to its knees.

The Renesas (formerly IDT) 8T49N222B-110NLGI8 was the industry standard solution for this problem.

Part of the FemtoClock® NG family, this chip is a Universal Frequency Translator (UFT). It takes a messy input clock, cleans it up using a high-performance PLL, and outputs a pristine, low-jitter signal. The specific "-110" version is factory-hardcoded for 156.25 MHz, the heartbeat of 10-Gigabit Ethernet.

However, this part is now Obsolete (EOL). This guide explains what made it special and how to manage its lifecycle.

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Table of Contents

• 1. Decoding the Part Number
• 2. Technical Specs: The Power of -110
• 3. The Obsolescence Challenge
• 4. Hardware Considerations: VFQFN-48
• 5. Sourcing & Replacements
• 6. Conclusion

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1. Decoding the Part Number

Renesas/IDT clock part numbers are precise. Here is the breakdown for 8T49N222B-110NLGI8:

Code Segment	Meaning	Detail
8T49N	Family	Universal Frequency Translator.
222	Outputs	2 Output Channels.
B	Revision	Silicon Revision B.
-110	Config	Factory Code. (Targeting 156.25 MHz).
NL	Package	48-VFQFN (7x7mm).
G	Material	Green (RoHS 6/6).
I	Temp	Industrial (-40°C to +85°C).
8	Packing	Tape & Reel. (For automated assembly).

Important: The "-110" is not random. It points to a specific register map burned into the chip's OTP memory at the factory, defining Input Dividers, Feedback Dividers, and Output Dividers to generate 156.25MHz from a standard crystal (e.g., 25MHz or 40MHz).

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2. Technical Specs: The Power of -110

This chip is designed to sit next to high-end PHYs and ASICs.

• Jitter Performance: < 0.5 ps RMS (12kHz - 20MHz integration). This "Femtosecond" performance is required to meet the strict bit error rate (BER) budgets of 10G/40G Ethernet.
• Frequency Translation: It can take a standard reference clock (like 25MHz) and multiply/clean it up to 156.25MHz.
• Redundancy: It supports Hitless Switching. If Input A fails, it can automatically switch to Input B without causing a phase jump that would crash the link.

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3. The Obsolescence Challenge

Status: EOL (End of Life). Renesas has moved to newer platforms like the RC22504A (System Synchronizer / Jitter Attenuator).

What this means for you:

1. Repair: You cannot simply buy a blank "8T49N222B" and expect it to work. You specifically need the -110 version, OR you need to program a blank "-000" version via I2C at boot time to match the -110 settings.
2. Redesign: The replacement parts are rarely pin-compatible. A PCB respin is usually required to migrate to newer clock synthesizers.

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4. Hardware Considerations: VFQFN-48

• Footprint: 7mm x 7mm, 48 leads.
• Thermal Pad: The exposed pad (ePad) on the bottom MUST be soldered to Ground. It acts as the primary heat sink.
• Power Supply Filtering: Clock chips are sensitive to noise. The VCC pins (2.5V or 3.3V) require careful ferrite bead and capacitor filtering to maintain jitter performance.

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5. Sourcing & Replacements

Since the part is obsolete, stock is scarce.

• Primary Replacement: Renesas RC22504A. (Newer, better performance, but different footprint).
• Drop-in Alternative: None. You must find NOS (New Old Stock) of the 8T49N222B series.
• Workaround: Buy the generic 8T49N222B-000 (Unprogrammed) or -999 (pre-programmed) and use an external MCU to write the configuration registers for 156.25MHz over the I2C bus during system boot.

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6. Conclusion

The Renesas 8T49N222B-110NLGI8 was a legendary component in the 10GbE era, providing the clean heartbeats for countless routers and switches. While it has reached the end of its life, understanding its "-110" configuration code is key to maintaining legacy equipment or programming generic replacements.

Sourcing Obsolete Clock Chips? Struggling to find EOL Renesas/IDT components? Visit Aichiplink.com to search for verified stock of 8T49N222B-110NLGI8.

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Written by Jack Elliott from AIChipLink.

 

AIChipLink, one of the fastest-growing global independent electronic   components distributors in the world, offers millions of products from thousands of manufacturers, and many of our in-stock parts is available to ship same day.

 

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