November 2006
rev 0.2
Spread Spectrum Selection
P2010A
Table 1 illustrates the 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/CLK, Pin 1).
Example of a typical printer or scanner application that operates on a clock frequency of 16MHz:
A spreading selection of FS0=1 and SR0=1 provides a percentage deviation of +/-2.50%* (see Table 1) of Center
Frequency. This results in the frequency on ModOUT being swept from 16.40MHz to 15.60MHz at a modulation rate of
33.33KHz (see Table 1). This particular example (see Figure below) given here is a common EMI reduction method for
scanner, printer or embedded applications and has already been adopted by most of the leading manufacturers.
Note: Spreading range selection varies from different system manufacturers and their designs.
P2010A Application Schematic for Flat-Bed Scanner
VDD
16MHz Crystal Input
1 XIN/CLK
2 XOUT
3 FS0
4 VSS
VDD 8
SR0 7
ModOUT 6
SSON 5
P2010A
0.1µF
Connected to CLK input pin of the system
Low Frequency EMI Reduction IC
Notice: The information in this document is subject to change without notice.
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