SM532 Datasheet, PDF (12/14 Pages) List of Unclassifed Manufacturers – Low EMI Spectrum Spread Clock

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YJGP VKOKPI KU ETKVKECN
Approved Product
SM532
Low EMI Sprectum Spread Clock
As can be seen from the figure above, the Fout/Time profile progresses through frequencies depending on where
it is in the sweep. If the frequency is in the middle of the sweep, the rate of change is slower compared to the rate
at the extremes of the band. When the frequency is nearing the end of the band, it is moving through these
frequencies faster, since it has to sweep through these same frequencies again after reversing direction. This
modulation profile is one of the key elements to the SM532. Using a linear sweep through all frequencies would
not give as good of results in EMI reduction.
APPLICATION NOTES AND SCHEMATICS
The schematic figure shown below is a simple minimum component application example of an SM532 design. In
the case shown below, the control lines are configured for the following parameters;
Input Frequency: Mid-Range Multiplier: X1 Modulation: 2.50%
Refer to loop filter values on Table 8, for operation at 3.3 Volts DC.
* L1 and C4 are required when Y1 is a 3rd. overtone crystal.
VCC = 3.3 VDC
R2
10 ohm.
C1
22 uf.
C2
0.1 uf.
VDD
SSON: On
C3
0.1 uf.
*
L1
330 nh.
Y1 ^{50 MHz}
C4 ^{.033 uf.}
*
27 pf. ^C5 27 pf. ^C8
VDD
1 _OSCin
2 _OSCout
14
R0
13 _R1
4 _S0
7
S1
11 _S2
9 _S3
8
SSON
SM532
12
Fout
Modulated Clock
Output
R1
1K
C6
10,000 pf.
C7
1000 pf.
Figure 9. Application Schematic
The SM532 has an internal Analog Power and Ground and a Digital Power and Ground. In the example above,
the digital and analog circuits are connected together. If noise is a concern, it is recommended that the Analog
and Digital Power and Grounds be separated. The loop filter shown above is recommended for operation at 3.14 -
3.47 VDC. This filter can also be used in 5.0 VDC operations when operating in the low frequency end of each of
the three input frequency ranges. Refer to table 8 on page 6 for complete information. Also note, the crystal, Y1,
is a third overtone 50 Mhz crystal, which requires an inductor and decoupling capacitor to OSCout.
International Microcircuits,Inc.
525 Los Coches St., Milpitas, 95035 408-263-6300, FAX [phone]
http:/www.imicorp.com
8/31/98
Rev. 1.4
Page 12 of 14