CY25100
Document #: 38-07499 Rev. *D
Page 2 of 11
General Description
The CY25100 is a Spread Spectrum Clock Generator (SSCG)
IC used for the purpose of reducing EMI found in today’s
high-speed digital electronic systems.
The device uses a Cypress proprietary PLL and Spread
Spectrum Clock (SSC) technology to synthesize and modulate
the frequency of the input clock. By frequency modulating the
clock, the measured EMI at the fundamental and harmonic
frequencies are greatly reduced. This reduction in radiated
energy can significantly reduce the cost of complying with
regulatory agency (EMC) requirements and improve
time-to-market without degrading system performance.
The CY25100 uses a factory/field-programmable configu-
ration memory array to synthesize output frequency, spread%,
crystal load capacitor, reference clock output on/off, spread
spectrum on/off function and PD#/OE options.
The spread% is programmed to either center spread or down
spread with various spread percentages. The range for center
spread is from ±0.25% to ±2.50%. The range for down spread
is from –0.5% to –5.0%. Contact the factory for smaller or
larger spread % amounts if required.
The input to the CY25100 can be either a crystal or a clock
signal. The input frequency range for crystals is 8–30 MHz,
and for clock signals is 8–166 MHz.
The CY25100 has two clock outputs, REFCLK and SSCLK.
The non-spread spectrum REFCLK output has the same
frequency as the input of the CY25100. The frequency
modulated SSCLK output can be programmed from 3–200
MHz.
The CY25100 products are available in an 8-pin SOIC and
TSSOP packages with commercial and industrial operating
temperature ranges.
Pin Description
Pin
Name
Description
1VDD
3.3V power supply.
2XOUT
Crystal output. Leave this pin floating if external clock is used.
3
XIN/CLKIN
Crystal input or reference clock input.
4
PD#/OE
Power-down pin: Active LOW. If PD# = 0, the PLL and Xtal are powered down,
and outputs are weakly pulled low.
Output Enable pin: Active HIGH. If OE = 1, SSCLK and REFCLK are enabled.
User has the option of choosing either PD# or OE function.
5
VSS
Power supply ground.
6REFCLK
Buffered reference output.
7
SSCLK
Spread spectrum clock output.
8
SSON#
Spread spectrum control. 0 = Spread on. 1 = Spread off.
Table 1.
Pin
Function
Input
Frequency
Total Xtal
Load
Capacitance
Output
Frequency
Spread Percent
(0.5% – 5%,
0.25% Intervals)
Reference
Output
Power-down or
Output Enable
Frequency
Modulation
Pin Name
XIN and
XOUT
XIN and XOUT
SSCLK
SSCLK
REFOUT
PD#/OE
SSCLK
Pin#
3 and 2
3 and 2
7
7
6
4
7
Unit
MHz
pF
MHz
%
On or Off
Select PD# or OE
kHz
Program
Value
ENTER DATA ENTER DATA
ENTER
DATA
ENTER DATA
ENTER
DATA
ENTER DATA
31.5
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