Cypress AN94024, Начало работы

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Getting Started with CY27410/30: 4-PLL Spread-Spectrum Clock Generator
www.cypress.com
Document No. 001-94024 Rev.*A 9
Cascading PLLs
With CY27410, you can make the output of one PLL and
provide it as an input to another PLL. This feature is called
PLL cascading. This feature can be used to generate very
precise frequencies using multiple dividers from two PLLs.
It can also take the VCFS modulated output from one PLL
and feed it to other PLLs, thus generating multiple
frequencies that track the change in the frequency.
Figure
27 shows PLL1 configured in VCFS mode, its output
cascaded to PLL2 and PLL3, but PLL4 will run as the fixed
(un-modulated) frequency generation.
Figure 27. Cascading PLLs
SSCG (Spread-Spectrum Clock Generator)
CY27410
’S spread-spectrum feature helps overcome
EMI/EMC concerns. The device supports both linear and
nonlinear spread profiles, and by using the patented
Lexmark profile as the nonlinear profile, offers the best
peak EMI reduction in the industry.
Figure 28 shows the scope sot for the Modulation Domain
Analyzer (time is plotted on the X-axis, while frequency is
shown on the Y-axis).
Figure 28. Spread Spectrum Clock Generator Profile
The spectrum is flat for nonlinear profiles, and raised at
the edges for linear profiles. In
Figure 29 , the nonspread-
spectrum profile is shown in red, while the modulated
nonlinear (Lexmark) and linear modulation spectrums,
~10 dB peak reduction at 633 MHz are shown in blue.
Figure 29. Spread-Spectrum Profiles Supported by
CY27410
-80.00
-75.00
-70.00
-65.00
-60.00
-55.00
-50.00
-45.00
-40.00
-35.00
-30.00
62
3.80
62
4.75
62
5.70
62
6.65
62
7.60
62
8.55
62
9.50
63
0.45
63
1.40
63
2.35
63
3.30
63
4.25
63
5.20
63
6.15
63
7.10
63
8.05
63
9.00
63
9.95
64
0.90
64
1.85
64
2.8
0
64
3.75
SS 1% Non-SS
Linear Profile