In the data center, fiber optics often steal the spotlight. But for cost-effective, short-distance connectivity (like Top-of-Rack connections), 10GBASE-T (Copper) remains king. It allows standard RJ45 Cat6a cables to carry 10 Gigabit speeds, leveraging existing infrastructure.
The muscle behind these ports is often the Broadcom BCM84758AKFSBLG.
This chip is a Quad-Port 10GBASE-T PHY, meaning a single chip drives four independent 10 Gigabit Ethernet ports. It is a staple in enterprise switches, high-end server NICs, and industrial networking gear.
This guide decodes the part number, explains the architecture, and addresses the notorious thermal challenges of 10G copper PHYs.
Table of Contents
- 1. Decoding the Part Number: BCM84758AKFSBLG
- 2. Architecture: 4x 10G over Copper
- 3. Thermal Management: The Challenge
- 4. Comparison: BCM84758 vs. Newer Generations
- 5. Conclusion
1. Decoding the Part Number: BCM84758AKFSBLG
Broadcom part numbers follow a strict logic. Here is what this specific string means:
The Breakdown Matrix
| Segment | Code | Meaning |
|---|---|---|
| Prefix | BCM | Broadcom Manufacturer Code. |
| Family | 84758 | Quad-Port 10GBASE-T PHY (847xx series). |
| Revision | A | Revision A Silicon. |
| Temp | K | Commercial Temperature (0°C to +70°C). |
| Package | FS | Fine-Pitch BGA (Ball Grid Array). |
| Env | BLG | RoHS Compliant (Lead-Free / Green). |
- Note: If you see a "B" or "C" revision (e.g., BCM84758BKFSBLG), it is usually a newer silicon stepping that fixes bugs or lowers power, but check the PCN (Product Change Notification) for drop-in compatibility.
Price Analysis & Stock Availability
This chip is widely used in legacy maintenance BOMs and refurbishment projects.
Procurement Tip: 10G PHYs are high-value items. [Check Stock for BCM84758AKFSBLG at Aichiplink] to source from verified distributors and avoid counterfeits.
2. Architecture: 4x 10G over Copper
The BCM84758 acts as a translator between the switch's brain and the outside world.
XFI/SFI Host Interface
On the "System Side" (facing the Switch ASIC), the BCM84758 uses the XFI (10 Gigabit Serial Interface).
- It takes 4 lanes of high-speed serial data from the switch core.
- It cleans up the signal (SerDes) and prepares it for transmission.
- This allows it to connect seamlessly to StrataXGS switches like the Trident or Tomahawk series without complex glue logic.
EEE (Energy Efficient Ethernet)
One of the key features of the BCM84758 is native support for IEEE 802.3az (EEE).
- Function: When no data is being sent, the PHY enters a "Low Power Idle" (LPI) mode.
- Benefit: This significantly reduces power consumption and heat generation during idle periods, which is crucial for large 48-port switches where thermal budgets are tight.
3. Thermal Management: The Challenge
If you have ever touched a 10G RJ45 transceiver, you know they get hot.
Why 10GBASE-T Runs Hot
Driving 10 Gigabits of data over 100 meters of copper wire requires sophisticated DSP (Digital Signal Processing) to cancel out echo and crosstalk (NEXT/FEXT).
- The BCM84758 performs billions of calculations per second to clean the signal.
- Design Requirement: Devices using this chip must have a dedicated heatsink and airflow. You cannot run this chip bare-die in an enclosed, fanless case.
- Comparison: Optical (SFP+) PHYs run much cooler because light transmission doesn't encounter the same electrical resistance and interference as copper.
4. Comparison: BCM84758 vs. Newer Generations
Broadcom has iterated on this design to improve power efficiency (process node shrinks).
| Feature | BCM84758 (This Chip) | BCM84848 | BCM84888 |
|---|---|---|---|
| Ports | 4 | 4 | 4 |
| Process | ~40nm Class | 28nm | 16nm / 7nm |
| Power/Port | High | Medium | Low |
| Multi-Gig | 10G/1G | 10G/1G | 2.5G / 5G (NBASE-T) |
| Status | Mature / EOL | Active | Active |
Verdict:
- The BCM84758 is excellent for standard 10G legacy support.
- If you need 2.5G/5G NBASE-T support (specifically for WiFi 6/6E Access Point uplinks), you need to look at the newer BCM84888 family.
6. Conclusion
The Broadcom BCM84758AKFSBLG is the engine behind the widespread adoption of 10G copper networking. By packing four ports of high-performance DSP into a single BGA package, it allowed enterprise switches to offer high-speed RJ45 connectivity at scale. While it requires careful thermal design, it remains a critical component in the networking ecosystem.
Sourcing High-Speed Networking Chips Maintain your network infrastructure with genuine parts. Visit Aichiplink.com to search for BCM84758AKFSBLG and other Broadcom Ethernet PHYs.
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.
We mainly source and distribute integrated circuit (IC) products of brands such as Broadcom, Microchip, Texas Instruments, Infineon, NXP, Analog Devices, Qualcomm, Intel, etc., which are widely used in communication & network, telecom, industrial control, new energy and automotive electronics.
Empowered by AI, Linked to the Future. Get started on AIChipLink.com and submit your RFQ online today!
Frequently Asked Questions
What is the BCM84758AKFSBLG used for?
It is a quad-port 10GBASE-T Ethernet PHY used in enterprise switches and server NICs.
How many ports does the BCM84758 support?
It supports four independent 10GbE RJ45 ports on a single chip.
Does BCM84758 support multi-gig speeds like 2.5G or 5G?
No. It supports 10G and 1G only (no NBASE-T).
Why does the BCM84758 require a heatsink?
10GBASE-T over copper generates high heat due to heavy DSP processing.
What is the system-side interface of BCM84758?
It uses XFI/SFI to connect to switch ASICs.
