PCIe fanout buffers simplify data centre timing

4th December 2014
Nat Bowers

Designed for data centre applications including servers, storage and switches, a family of PCIe Gen1/2/3 fanout buffers has been introduced by Silicon Labs. The Si5310x/11x/019 family has been designed for today’s leading x86 motherboard and server systems and the devices are claimed to be the industry’s most power-efficient fanout buffers.

Data centre equipment makers have had a limited supplier base for PCIe Gen3 buffers approved by the leading x86 CPU and chipset supplier. These conventional PCIe buffers are based on power-hungry constant-current output technology, which increases BOM count by requiring four external termination resistors per output, as well as one reference resistor. Developers are increasingly seeking components that deliver the utmost energy efficiency while complying with stringent x86 board specifications.

Available with a selection of output count options, the PCIe buffers are qualified for use in 98% of x86-based server/storage motherboard designs. Silicon Labs’ Si5310x/11x/019 family provides equipment makers with lower power, standards-compliant PCIe buffer products qualified by the leading x86 CPU and chipset supplier and backed by an outstanding technical support organisation. More than 90% of existing motherboard designs use PCIe buffers based on constant-current output technology. To address this existing market need, Silicon Labs’ Si53019 PCIe constant-current buffer delivers a fully qualified drop-in compatible solution with 30% lower power than conventional solutions.

Silicon Labs’ Si5310x and Si5311x devices use an innovative push-pull output architecture to deliver the industry’s lowest power family of PCIe buffers. These devices consume 60% less power than constant-current buffers while reducing the required number of external resistors per output, significantly reducing external component count and simplifying PCB design. For example, using Silicon Labs’ 19-output Si53119 push-pull buffer instead of a conventional constant-current device can save nearly 1W and eliminate 39 external components.

The push-pull output devices are also optimal PCIe timing solutions for system designs using new ARM-based SoCs targeting the hyperscale server and storage markets. Similar to x86-based designs, ARM-based SoC platforms for the server and storage markets use PCIe as the primary system data bus and interconnect. With system-level power efficiency being a major benefit of the hyperscale architecture, the Si5310x and Si5311x are suited for all server and storage platform designs, regardless of CPU architecture.

Data centre equipment makers also face the challenge of maintaining signal integrity while driving clocks between boards over cables up to 60" in length. A PCIe clock’s rise and fall times degrade and slow down over such long distances, resulting in reduced jitter performance and increased system packet loss failures. Silicon Labs’ PCIe Gen3 buffers are designed to drive long clock signal traces while maintaining standards-compliant PCIe rise and fall time specifications to prevent excessive jitter and packet loss.

Silicon Labs’ PCIe buffer family includes 6, 8, 12, 15 and 19-output devices as well as a combination of constant-current and push-pull buffers, enabling developers to tailor the optimal solution for each application. Silicon Labs’ devices are pin- and functionally compatible replacements for conventional PCIe buffers, providing developers with superior alternatives that improve power efficiency, signal integrity and jitter performance.

James Wilson, Marketing Director, Timing Products, Silicon Labs, comments: “Mobile Internet traffic and cloud computing are driving the need for faster, higher performance data centre equipment requiring high-precision timing solutions supporting both the PCIe standard and leading x86 specifications. We’ve expanded our PCIe timing portfolio to include fully x86-qualified PCIe Gen3 fanout buffers that reduce the power, cost and complexity of data centre equipment. Our PCIe products complement Silicon Labs’ any-frequency clock generators by providing a single-chip clock tree solution for any server, switch or storage design.”

Samples and production quantities of the Si531xx and Si53019 PCIe fanout buffers are available now. Pricing for the Si531xx push-pull output buffers begins at $1.70 in 10,000 unit quantities, and the Si53019 constant-current output buffer is priced at $2.85 in 10,000 unit quantities.

To accelerate development of server and storage applications based on push-pull output clock buffers, Silicon Labs offers the Si53108-EK, Si53112-EK and Si53119-EK evaluation boards, each priced at $125.

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