Spread Spectrum Frequency Timing Generator
W166
Cypress Semiconductor Corporation
•
3901 North First Street
•
San Jose
•
CA 95134
•
408-943-2600
December 20, 1999, rev. **
Features
• Maximized EMI suppression using Cypress’s Spread
Spectrum technology
• Generates a spread spectrum copy of the provided
input
• Selectable spreading characteristics
• Integrated loop filter components
• Operates with a 3.3V or 5V supply
• SSON# pin enables frequency spreading
• Low power CMOS design
• Available in 8-pin SOIC (Small Outline Integrated
Circuit)
Overview
The W166 incorporates the latest advances in PLL spread
spectrum frequency synthesizer techniques. By frequency
modulating the output with a low-frequency carrier, peak EMI
is greatly reduced. Use of this technology allows systems to
pass increasingly difficult EMI testing without resorting to cost-
ly shielding or redesign.
In a system, not only is EMI reduced in the various clock lines,
but also in all signals which are synchronized to the clock.
Therefore, the benefits of using this technology increase with
the number of address and data lines in the system. The Sim-
plified Block Diagram shows a simple implementation.
Table 1. Frequency Spread Selection
W166
Input
Frequency
(MHz)
Output
Frequency (MHz)
FS1
FS0
0
0
50 to 65
fIN ±0.625%
0
1
50 to 65
fIN ±1.25%
1
0
50 to 65
fIN ±2.5%
1
1
50 to 65
fIN –3.75%
Simplified Block Diagram
Pin Configuration
Oscillator or Reference
Spread Spectrum
W166
(EMI suppressed)
3.3V or 5V
Input
Output
8
7
6
5
1
2
3
4
CLKIN
NC
GND
FS1
SSON#
CLKOUT
FS0
VDD
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