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Resumen del manual
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 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. 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 application. 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 applications requiring 80- to 140-MHz frequency range. 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 Block Diagram Pin Configuration Phase Detector VCO Xin Xout 10 pF. Reference Divider 8 pF 8 pF 250 K VCO / N Modulation Control Input Control Logic Output Divider and Mux Power Contol Logic 3(5) 7(1)5(7) 4(6) VDD S0S1 FSOUT Loop Filter VSS 6(8) VSS VDD (TSSOP Pin #) Xin Xout S1 LF VDD S0 FSOUT VSS 8 Pin SOIC Package S0 VDD Xin Xout FSOUT VSS LF S1 8 Pin TSSOP Package 1(3) 2(4) 8(2) 1 2 3 4 8 7 6 5 FS78x 1 2 3 4 8 7 6 5 FS78x Pin Description Pin Name I/O Type Description 1/2 (SOIC) 3/4 (TSSOP) XIN/XOUT 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 is connected to an external clock other than crystal, leave XOUT (pin 2) unconnected. 7/3 (SOIC) 1/5 (TSSOP) S0 / S1 I CMOS/TTL Digital control inputs to select input frequency range and outputfrequency scaling. Refer to Table 2 and Table 3 for selection. S0 has internal pull-down. S1 has internal pull-up. 4 (SOIC) 6 (TSSOP) LF I Analog Loop Filter. Single ended three-state output of the phase detector. A two-pole passive loop filter is connected to LF. 6 (SOIC) 8 (TSSOP) FSOUT 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. 8 (SOIC) 2 (TSSOP) VDD P Power Positive Power Supply. 5 (SOIC) 7 (TSSOP) VSS P Power Power Supply Ground. 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 The following table provides a list of recommended loop filter LF (pin 4) 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...
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