25 MHz

25 MHz

FPGA

48 MHz

25 MHz

100 MHz

WiFi

40 MHz

Crystals + Oscillators

Crystals:4

Oscillators: 2

Clock: None

1 x Crystal + 1 x Clock

Crystals: 1

Oscillators: None

Clock: 1

USB

Controller

USB

Controller

DP838xx

10/100 PHY

DP838xx

10/100 PHY

CDCE(L)9xx

Clock

WiFi

FPGA

25 MHz

Copyright © 2016, Texas Instruments Incorporated

24

CDCE925, CDCEL925

SCAS847I – JULY 2007 – REVISED OCTOBER 2016

www.ti.com

Product Folder Links: CDCE925 CDCEL925

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Copyright © 2007–2016, Texas Instruments Incorporated

10 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.

10.1 Application Information

The CDCEx925 device is an easy-to-use high-performance, programmable CMOS clock synthesizer. it can be

used as a crystal buffer, clock synthesizer with separate output supply pin. The CDCEx925 features an on-chip

loop filter and Spread-spectrum modulation. Programming can be done through SPI, pin-mode, or using on-chip

EEPROM. This section shows some examples of using CDCEx925 in various applications.

10.2 Typical Application

Figure 15 shows the use of the CDCEx925 devices for replacement of crystals and crystal oscillators on a

Gigabit Ethernet Switch application.

Figure 15. Crystal and Oscillator Replacement Example

10.2.1 Design Requirements

CDCEx925 supports spread spectrum clocking (SSC) with multiple control parameters:

•

Modulation amount (%)

•

Modulation frequency (>20 kHz)

•

Modulation shape (triangular)

•

Center spread / down spread (± or –)