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FS781

更新时间: 2024-11-02 03:37:55
品牌 Logo 应用领域
赛普拉斯 - CYPRESS 时钟
页数 文件大小 规格书
12页 197K
描述
Low EMI Spectrum Spread Clock

FS781 数据手册

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FS781/82/84  
Low EMI Spectrum Spread Clock  
Features  
Functional Description  
The Cypress FS781/82/84 are Spread Spectrum clock  
generator ICs (SSCG) designed for the purpose of reducing  
electromagnetic interference (EMI) found in today’s  
high-speed digital systems.  
• Spread Spectrum clock generator (SSCG) with 1×, 2×,  
and 4× outputs  
• 6- to 82-MHz operating frequency range  
• Modulates external clocks including crystals, crystal  
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.  
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  
Cypress Semiconductor Corporation  
3901 North First Street  
San Jose, CA 95134  
408-943-2600  
Document #: 38-07029 Rev. *E  
Revised January 28, 2005  

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