SM532 Datasheet, PDF (7/14 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
Loop Filters
The SM532 requires an external loop filter to provide the proper operation and modulation profile for a given input
frequency. The loop filter is connected to pin 5 (LF) of the SM532 and is a typical 2 pole low pass filter. Since the
SM532 operates over such a wide range of frequencies, the loop filter will change depending on the frequency of
operation. The following loop filter values are recommended for best performance and modulation profile at 3.0
volts and 5.0 volts VDD. Operating voltage is measured at the VDD pin of the SM532.
Notice that the selection of Loop Filter values only depends on the input frequency and VDD voltage, and
LF #1
LF #2
LF #3
LF
LF
LF
R1
1 K ohm
C6
10,000 pF
C7
1,000 pF
R1
1.5 K ohm
C6
6,800 pF
C7
680 pF
R1
2 K ohm
C6
3,900 pF
C7
390 pF
does not depend on the R and S settings.
Figure 3. Recommended Loop Filters
Input
Range
Low
Middle
High
Input
Range
Low
Low
Low
Middle
Middle
Middle
High
High
High
VDD +/-5%
3.3
3.3
3.3
VDD +/-10%
5.0
5.0
5.0
Recommended Loop Filter Values
Input Frequency
Range (MHz)
R1 (KΩ)
C6 (pF)
14.0 to 22.5
1.0
10,000
25.0 to 45.0
1.0
10,000
50.0 to 90.0
1.0
10,000
Input Frequency
Range (MHz)
R1 (KΩ) C6 (pF)
14.0 to 19.9
20.0 to 24.9
1.0
10,000
1.5
6,800
25.0 to 29.9
2.0
3,900
5.0
30.0 to 39.9
1.0
10,000
5.0
40.0 to 49.9
1.5
6,800
5.0
50.0 to 59.9
2.0
3,900
5.0
60.0 to 79.9
1.0
10,000
5.0
80.0 to 99.9
1.5
6,800
5.0
100.0 to 120.0
2.0
3,900
Table 8
C7 (pF)
1,000
1,000
1,000
C7 (pF)
1,000
680
390
1,000
680
390
1,000
680
390
Loop
Filter #
1
1
1
Loop
Filter #
1
2
3
1
2
3
1
2
3
The component values listed in Table 8 are recommended values using commonly manufactured components.
Note that there are actually 3 different sets of loop filter values. Due to the VCO characteristics, the table is
divided in to 3 volt operation and 5 volt operation. Referring to the table above, it is apparent that one set of loop
filter values is all that is needed in the 3 volt operation. In the 5 volt operation, each input operating range is
divided into 3 sections which require a different loop filter for optimal performance. The best loop filter for any
application is the one that, provides the greatest EMI reduction, maintains system integrity, has a modulation
profile shown on page 7 and uses commonly available components.
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 7 of 14