PCIe Gen 4-5

Clock

Generator

CDCDB2000

20x LP-HSCL Output Buffer

SMBus

Control

OE#

Control

LP-HCSL

PCIe PHY

PCIe PHY

PCIe PHY

PCIe PHY

LP-HCSL

20

PCIe PHY

PCIe PHY

PCIe Device

Side-Band

Interface

Control Interface

24

CDCDB2000

SNAS787 – NOVEMBER 2019

www.ti.com

Product Folder Links: CDCDB2000

Submit Documentation Feedback

Copyright © 2019, Texas Instruments Incorporated

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The CDCDB2000 is a fanout buffer that supports PCIe generation 4 and PCIe generation 5 REFCLK distribution.

It is used to create, and distribute, up to 20 copies of a typically 100-MHz clock.

8.2 Typical Application

Figure 10 shows a CDCDB2000 typical application. In this application, a clock generator provides a 100-MHz

reference to the CDCDB2000 which then distributes that clock to PCIe endpoints. The clock generator may be a

discrete clock generator like the LMK03328 or it may be integrated in a larger component such as a PCH or

application processor.

Figure 10. Typical Application

8.2.1 Design Requirements

Consider a typical server motherboard application which needs to distribute a 100-MHz PCIe reference clock

from the PCH of a processor chipset to multiple endpoints. An example of clock input and output requirements is:

•

Clock Input:

–

100-MHz LP-HCSL

•

Clock Output:

–

2x 100-MHz to processors, LP-HCSL

–

2x 100-MHz to riser/retimer, LP-HCSL

–

2x 100-MHz to DDR memory controller, LP-HCSL

The section below describes the design procedure to configure the CDCDB2000 to output the frequencies for the

above scenario.

8.2.2 Detailed Design Procedure

The following items must be determined before starting design of a CDCDB2000 socket:

•

Output Enable Control Method

•

SMBus address