November 2006

P2005A/S

rev 1.3

Low Frequency EMI Reduction IC

3 of 8

Notice: The information in this document is subject to change without notice.

Spread Spectrum

The Output Frequency Selection Table and the Frequency Deviations Selections Table illustrate the two possible spread

spectrum options. The optimal setting should minimize system EMI to the fullest without affecting system performance. The

spreading is described as a percentage deviation of the center frequency (Note: The center frequency is the frequency of the

external reference input on CLKIN, Pin1).

Example:

The P2005A/S is designed for communications, digital video and imaging applications. It is not only optimized for operation

in the 8MHz – 32MHz range, but its output frequency can be extended down to one half of the input clock frequency using

the divide-by-two feature. This feature extends low frequency as low as to 4MHz. Setting Pin 3 low (DIV2 = 0; Divide-by-two

mode) sets the output frequency (ModOUT) to half the frequency of the input clock (CLKIN). This is a simple way to generate

a spread spectrum modulated low frequency clock when only a higher frequency signal is available. If you want the output

frequency to be the same as the input, you can either set DIV2=1 or leave it unconnected.

Selecting the P2005A/S’s spread options is a matter of either setting SR0=1 or SR0=0. Setting SR0=0 set as a lower

modulation spread, while setting it to 1 introduces a wider spectral spread in the output clock. Refer Modulation output and

Spreading Selections Tables. The example given in the figure below shows the device set to the divide-by-two mode

(DIV2=0) with a lower spectrum range (SR0=0). The versatility provided by allowing both clock division and spread spectrum

on one chip is already proving to be a popular solution among leading system manufacturers.

P2005A/S Application Schematic

1

2

3

4

CLKIN

XOUT

DIV2

VSS

MODOUT

5

6

7

8

SR0

SSON#

VDD

8.832MHz Crystal

Modulated 4.416MHz is

connected to CLK input

pin of the system

+3.3V

0.1µF

P2005A/S