July 2005

P2008A

rev 1.3

General purpose EMI Reduction IC

3 of 9

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

Spread Spectrum

The Modulation Output and Spreading Selection Tables 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

XIN/CLKIN, Pin1).

Example:

The P2008A is designed for communications, digital video and imaging applications. It is not only optimized for operation in

the 4MHz – 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 2MHz. Setting Pin 3 low (DIV2 = 0; Divide-by-two

mode) sets the output frequency (ModOUT) to half the frequency of the input clock (XIN/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 P2008A’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.

P2008A Application Schematic

Modulated 4.416MHz is

connected to CLK input

pin of the system

1

2

3

4

XIN/CLKIN

XOUT

DIV2

VSS

SR0

5

6

7

8

SSON#

Mod OUT

VDD

8.832MHz Crystal

+3.3V

0.1µF

P2008A