FS781/82/84 Low EMI Spectrum Spread Clock Features Functional Description The Cypress FS781/82/84 are Spread Spectrum clock Spread Spectrum clock generator (SSCG) with 1, 2, generator ICs (SSCG) designed for the purpose of reducing and 4 outputs electromagnetic interference (EMI) found in todays 6- to 82-MHz operating frequency range high-speed digital systems. Modulates external clocks including crystals, crystal The FS781/82/84 SSCG clocks use a Cypress-proprietary oscillators, or ceramic resonators technology to modulate the input clock frequency, XIN, by modulating the frequency of the digital clock. By modulating Programmable modulation with simple R-C external the reference clock the measured EMI at the fundamental and loop filter (LF) harmonic frequencies of FSOUT is greatly reduced. This Center spread modulation reduction in radiated energy can significantly reduce the cost 3V-5V power supply of complying with regulatory requirements without degrading digital waveforms. TTL-/CMOS-compatible outputs The Cypress FS781/82/84 clocks are very simple and Low short-term jitter versatile devices to use. By programming the two range select Low-power Dissipation lines, S0 and S1, any frequency from 6- to 82-MHz operating range can be selected. The FS781/2/4 are designed to 3.3 VDC = 37 mW typical operate over a very wide range of input frequencies and 5.0 VDC = 115 mW typical provides 1, 2, and 4 modulated clock outputs. Available in 8-pin SOIC and TSSOP packages The FS78x devices have a simple frequency selection table that allows operation from 6 MHz to 82 MHz in four separate Applications ranges. The bandwidth of the frequency spread at FSOUT is determined by the values of the loop filter components. The Desktop/notebook computers modulation rate is determined internally by the input frequency Printers, copiers, and MFP and the selected input frequency range. Scanners and fax 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 LCD displays and monitors loop filter value. Refer to the Loop Filter Selection chart in CD-ROM, VCD, and DVD Table 2 and Table 3 for the recommended values. Due to a Automotive and embedded systems wide range of application requirements, an external loop filter (LF) is used on the FS78x products. The user can select the Networking, LAN/WAN exact amount of frequency modulation suitable for the appli- Digital cameras and camcorders cation. Using a fixed internal loop filter would severely limit the use of a wide range of modulation bandwidths (Spread %) Modems to a few discrete values. Refer to FS791/2/4 products for appli- cations requiring 80- to 140-MHz frequency range. 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 198 Champion Court San Jose, CA 95134-1709 408-943-2600 Document : 38-07029 Rev. *F Revised January 2, 2005 + Feedback FS781/82/84 Pin Configuration Block Diagram Loop Filter 4(6) Xin 1 8 VDD 250 K Xout 2 7 S0 FS78x S1 3 6 FSOUT Reference 1(3) Xin Divider Phase 8 pF LF 4 5 VSS Detector VCO 10 pF. 8 Pin SOIC Package Modulation Control 2(4) Xout 8 pF VCO / N S0 1 8 FSOUT Output VDD 2 7 VSS FS78x Divider Power Contol 8(2) VDD Input Control Logic 6(8) VDD FSOUT and Logic Xin 3 6 LF Mux Xout 4 5 S1 VSS (TSSOP Pin ) 5(7) 3(5) 7(1) 8 Pin TSSOP Package VSS S1 S0 Pin Description Pin Name I/O Type Description 1/2 (SOIC) X /X I/O Analog Pins form an on-chip reference oscillator when connected to terminals IN OUT 3/4 (TSSOP) of an external parallel resonant crystal. X may be connected to IN TTL/CMOS external clock source. If X is connected to an external clock IN other than crystal, leave X (pin 2) unconnected. OUT 7/3 (SOIC) S0 / S1 I CMOS/TTL Digital control inputs to select input frequency range and output 1/5 (TSSOP) frequency scaling. Refer to Table 2 and Table 3 for selection. S0 has internal pull-down. S1 has internal pull-up. 4 (SOIC) LF I Analog Loop Filter. Single ended three-state output of the phase detector. A two-pole 6 (TSSOP) passive loop filter is connected to LF. 6 (SOIC) FSOUT O CMOS/TTL Modulated Clock Frequency Output. The center frequency is the same as 8 (TSSOP) the input reference frequency for FS781. Input frequency is multiplied by 2 and 4 for FS782 and FS784, respectively. 8 (SOIC) V P Power Positive Power Supply. DD 2 (TSSOP) 5 (SOIC) V P Power Power Supply Ground. SS 7 (TSSOP) Output Frequency Selection Table 1. FSOUT SSCG (Modulated Output Clock) Product Selection Product Number FSOUT Frequency Scaling Description FS781 1 1 modulated frequency of input clock FS782 2 2 modulated frequency of input clock FS784 4 4 modulated frequency of input clock Loop Filter Selection Chart R6 LF (pin 4) The following table provides a list of recommended loop filter values for the FS781/82/84. The FS78X is divided into four C8 C7 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. Document : 38-07029 Rev. *F Page 2 of 12 + Feedback