CY25901 Cypress Semiconductor, CY25901 Datasheet - Page 2

• Manufacturer Part Number: CY25901
• Description: Spread Spectrum Clock Generator
• Manufacturer: Cypress Semiconductor

Document #: 38-07521 Rev. **
Pin Description
Spread Spectrum Clock Generator
Spread Spectrum Clock Generator (SSCG) is a frequency
modulation technique used to reduce EMI radiation generated
by repetitive digital signals, mainly clocks. A clock radiates EM
energy at its fundamental frequency as well as its harmonics.
Spread Spectrum distributes this energy over a small
frequency bandwidth, and decreasing the peak value of
Pin No.
1
2
3
4
5
6
7
8
CLKOUT
VDD
VSS
XIN
XOUT
SSSEL
REFOUT
SSON#
Name
PWR
PWR
I/O
O
O
O
I
I
I
Spread Spectrum Clock Output. See Table 1 for frequency selections.
Power Supply.
Common Ground.
Oscillator Buffer Input. Connect to an external parallel resonant crystal or externally generated
reference clock.
Oscillator Buffer Output. Connect to an external parallel resonant crystal. Do not connect when
an externally generated reference clock is applied at XIN.
Spread Spectrum Select Input. See Table 1. internally pulled up.
Buffered Output of XIN.
Spread Spectrum Enable Input. When asserted low, Spread Spectrum is enabled.
Internally pulled down.
-10
-20
-30
-40
-50
-60
-70
-80
0
38
Figure 1. Modulation Frequency Profile
38
Figure 2. Spread Spectrum
39
39
Frequency(MHz)
Spread Spectrum
40
radiated energy over the spectrum. This technique is achieved
by modulating the clock around or below the center of its
reference frequency by a certain percentage (which also
determines the energy distribution bandwidth).
The SSCG function is enabled when SSON pin is set to low.
Resulting in a spread bandwidth that is center spread, amount
as selected by SSSEL (see Table 1).
41
41
Description
42
43
SS-ON
SS-OFF
CY25901
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