October 2003

ASM3X2105A

rev 1.0

Low Frequency EMI Reduction

3 of 10

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

1

2

3

4

CLKIN

XOUT

DIV2

VSS

MODOUT

5

6

7

8

SR0

SSON#

VDD

ASM3X2105A

Spread Spectrum

Spreading the spectrum of the signal reduces the system EMI. 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 ASM3X2105A is designed for communications, digital video and imaging applications. It is not only

optimized for operation in the 6MHz – 12MHz 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 operation to as

low as 3MHz. 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.

8.832MHz Crystal

Modulated 4.416MHz

is connected to CLK

input pin of the system

+5V

0.1µF