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Cypress Semiconductor Electronic Components Datasheet

IMIFS781 Datasheet

(IMIFS781/82/84) Low EMI Spectrum Spread Clock

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FS781/82/84
Features
• Spread Spectrum clock generator (SSCG) with 1×, 2×,
and 4× outputs
• 6- to 82-MHz operating frequency range
• Modulates external clocks including crystals, crystal
oscillators, or ceramic resonators
• Programmable modulation with simple R-C external
loop filter (LF)
• Center spread modulation
• 3V-5V power supply
• TTL-/CMOS-compatible outputs
• Low short-term jitter
• Low-power Dissipation
— 3.3 VDC = 37 mW – typical
— 5.0 VDC = 115 mW – typical
• Available in 8-pin SOIC and TSSOP packages
Applications
• Desktop/notebook computers
• Printers, copiers, and MFP
• Scanners and fax
• LCD displays and monitors
• CD-ROM, VCD, and DVD
• Automotive and embedded systems
• Networking, LAN/WAN
• Digital cameras and camcorders
• Modems
Benefits
• Programmable EMI reduction
• Fast time to market
• Lower cost of compliance
• No degradation in rise/fall times
• Lower component and PCB layer count
Low EMI Spectrum Spread Clock
Description
The Cypress FS781/82/84 are Spread Spectrum clock
generator ICs (SSCG) designed for the purpose of reducing
electromagnetic interference (EMI) found in todays
high-speed digital systems.
The FS781/82/84 SSCG clocks use a Cypress-proprietary
technology to modulate the input clock frequency, XIN, by
modulating the frequency of the digital clock. By modulating
the reference clock the measured EMI at the fundamental and
harmonic frequencies of FSOUT is greatly reduced. This
reduction in radiated energy can significantly reduce the cost
of complying with regulatory requirements without degrading
digital waveforms.
The Cypress FS781/82/84 clocks are very simple and
versatile devices to use. By programming the two range select
lines, S0 and S1, any frequency from 6- to 82-MHz operating
range can be selected. The FS781/2/4 are designed to
operate over a very wide range of input frequencies and
provides 1×, 2×, and 4× modulated clock outputs.
The FS78x devices have a simple frequency selection table
that allows operation from 6 MHz to 82 MHz in four separate
ranges. The bandwidth of the frequency spread at FSOUT is
determined by the values of the loop filter components. The
modulation rate is determined internally by the input frequency
and the selected input frequency range.
The Bandwidth of these products can be programmed from as
little as 1.0% up to as much as 4.0% by selecting the proper
loop filter value. Refer to the Loop Filter Selection chart in
Table 2 and Table 3 for the recommended values. Due to a
wide range of application requirements, an external loop filter
(LF) is used on the FS78x products. The user can select the
exact amount of frequency modulation suitable for the appli-
cation. Using a fixed internal loop filter would severely limit
the use of a wide range of modulation bandwidths (Spread %)
to a few discrete values. Refer to FS791/2/4 products for appli-
cations requiring 80- to 140-MHz frequency range.
Block Diagram
250 K
Xin 1(3)
8 pF
Xout 2(4)
8 pF
Reference
Divider
Modulation
Control
VDD 8(2)
Power Contol
Logic
VDD Input Control Logic
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5(7)
VSS
3(5) 7(1)
S1 S0
Pin Configuration
Loop Filter
4(6)
Phase
Detector
10 pF.
VCO
VCO / N
Output
Divider
and
Mux
VSS
(TSSOP Pin #)
Xin
Xout
S1
LF
18
2 FS78x 7
36
45
VDD
S0
FSOUT
VSS
8 Pin SOIC Package
S0
VDD
6(8) FSOUT
Xin
Xout
18
2 FS78x 7
36
45
FSOUT
VSS
LF
S1
8 Pin TSSOP Package
Cypress Semiconductor Corporation • 3901 North First Street • San Jose • CA 95134 • 408-943-2600
Document #: 38-07029 Rev. *C
Revised December 14, 2002


Cypress Semiconductor Electronic Components Datasheet

IMIFS781 Datasheet

(IMIFS781/82/84) Low EMI Spectrum Spread Clock

No Preview Available !

www.DataSheet4U.com
FS781/82/84
Pin Description
Pin
1/2 (SOIC)
3/4 (TSSOP)
Name
XIN/XOUT
7/3 (SOIC) S0 / S1
1/5 (TSSOP)
4 (SOIC)
6 (TSSOP)
6 (SOIC)
8 (TSSOP)
LF
FSOUT
8 (SOIC)
2 (TSSOP)
5 (SOIC)
7 (TSSOP)
VDD
VSS
I/O Type
Description
I/O Analog
Pins form an on-chip reference oscillator when connected to terminals
of an external parallel resonant crystal. XIN may be connected to
TTL/CMOS external clock source. If XIN connected to external clock other
than crystal, leave XOUT (pin 2) unconnected.
I CMOS/TTL Digital control inputs to select input frequency range and output
frequency scaling. Refer to Table 2 and Table 3 for selection. S0 has internal
pull-down. S1 has internal pull-up.
I Analog
Loop Filter. Single ended three-state output of the phase detector. A two-pole
passive loop filter is connected to LF.
O CMOS/TTL Modulated Clock Frequency Output. The center frequency is the same as
the input reference frequency for FS781. Input frequency is multiplied by 2×
and 4× for FS782 and FS784, respectively.
P Power
Positive Power Supply.
P Power
Power Supply Ground.
Output Frequency Selection
Table 1. FSOUT SSCG (Modulated Output Clock) Product Selection
Product Number
FS781
FS782
FS784
FSOUT Frequency Scaling
1×
2×
4×
Description
1× modulated frequency of input clock
2× modulated frequency of input clock
4× modulated frequency of input clock
Loop Filter Selection Chart
The following table provides a list of recommended loop filter
values for the FS781/82/84. The FS78X is divided into four
ranges and operated at both 3.3V and 5.5 VDC. The loop filter
at the right is representative of the loop filter components in
Table 2.
LF (pin 4)
R6
C8
C7
Table 2. FS781/82/84 Recommended Loop Filter Values C7 (pF) @ +3.3 VDC ±5% (R6 = 3.3K)[1, 2, 3, 4]
Input MHz S1 S0 BW = 1.0%[3] BW = 1.5%[3] BW = 2.0%[3] BW = 2.5%[3] BW = 3.0%[3] BW = 3.5%[3] BW = 4.0%[3]
6
0 0 10,000/1000
1550
910
780
700
640
560
8 0 0 10,000/330
990
820
640
520
450
400
10 0 0
1040
680 460 360 300 240 210
12 0 0
830
420 300 220 200 190 170
14 0 0
580
230 200 160 140 100
80
16 0 1
10000
980
760
580
470
410
385
18 0 1
1200
750 580 470 415 370 300
20 0 1
1000
730 470 390 320 220 190
22 0 1
960
640 410 270 230 200 180
24 0 1
920
400 250 210 180 160 150
26 0 1
660
300 220 180 150 140 120
Notes:
www.DataSheet4U.com1. If the value selected from the above chart is not a standard, use the next available larger value.
2. All bandwidths indicated above are total peak-to-peak spread. 1% = +0.5% to 0.5%. 4% = +2.0% to 2.0%.
3. If C8 is not listed in the chart for a particular bandwidth and frequency, it is not used in the loop filter.
4. Contact Cypress for LF values less than 1.0% bandwidth.
Document #: 38-07029 Rev. *C
Page 2 of 11


Part Number IMIFS781
Description (IMIFS781/82/84) Low EMI Spectrum Spread Clock
Maker Cypress Semiconductor
Total Page 11 Pages
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