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Cypress Semiconductor FS781 manual

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Table of contents for the manual

  • Page 1

    Low EMI S pectrum S pread Clock FS781/82/84 Cypress Semiconductor Corpora tion • 198 Champion Cou rt • San Jose , CA 95134-1 709 • 408-943-2 600 Document #: 38-07029 Rev . *F Revised January 2, 2005 Features • Spread S pectrum clock generator (SSCG) with 1×, 2× , and 4× outpu t s • 6- to 82-MHz operating freq u ency range • Modulates[...]

  • Page 2

    FS781/82/84 Document #: 38-07029 Rev . *F Page 2 of 12 Output Frequency Selection Loop Filter Selection Chart The following table provides a list of recommended l oop filter values for the FS781/82/84. T he 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 com[...]

  • Page 3

    FS781/82/84 Document #: 38-07029 Rev . *F Page 3 of 12 T ab le 2. FS781/82/8 4 Recommended Loop Filter V alu es 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 6 40 560 8 0 0 10,000/330 990 820 640 [...]

  • Page 4

    FS781/82/84 Document #: 38-07029 Rev . *F Page 4 of 12 T ab le 3. FS781/82/8 4 Recommended Loop Filter V alu es C7 (pF) @ +5.0 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 1 140 1030 930 8 30 710 610 510 8 0 0 1 170 970 740 570 4 60 400 280[...]

  • Page 5

    FS781/82/84 Document #: 38-07029 Rev . *F Page 5 of 12 SSCG Modulation Profile The digital control inputs S0 and S1 determine th e modulation frequency of FS781/2/4 products. The input freque ncy is divided by a fixed number, depending on the operating range that is selected. The modulation frequency of the FS78x can be determined from Ta b l e 4 .[...]

  • Page 6

    FS781/82/84 Document #: 38-07029 Rev . *F Page 6 of 12 From the above parameters, the output clock at FSOUT will be sweeping symmetrically around a center frequency of 20 MHz. The minimum and maximu m extremes of this clock will be +200 kHz and –200 kHz. So we have a clock that is sweeping from 19.8 MHz to 20.2 MHz and back again. If we were to l[...]

  • Page 7

    FS781/82/84 Document #: 38-07029 Rev . *F Page 7 of 12 ** ** Occasionally , C8 is us ed to create a s econd pole fo r this l oop filter. Refer to Loop Filter Selec tion table. Mount l oop filter c ompo nents as close to LF pin as possible . . Crystal is 2 0 MHz is 1st Orde r with 18 pF l oad capa citance. If Crystal l oad capacita nce is differe nt[...]

  • Page 8

    FS781/82/84 Document #: 38-07029 Rev . *F Page 8 of 12 Absolute Maximum Ratings [6] This device contains circuitry to protect the input against damage due to high static voltages or electric fields; however , precautions should b e taken to avoid application of any voltage higher than the absolute maxi mum rated voltages to this circuit. For proper[...]

  • Page 9

    FS781/82/84 Document #: 38-07029 Rev . *F Page 9 of 12 CCJ FSOUT , Cycle-to-Cycle Jitter , 48 MHz @ 3.30 VDC (Pin 6) – 320 370 ps CCJ FSOUT , Cycle-to-Cycle Jitter , 48 MHz @ 5.0 VDC (Pin 6) – 310 360 ps CCJ FSOUT , Cycle-to-Cycle Jitter , 72 MHz @ 3.30 VDC (Pin 6) – 270 325 ps CCJ FSOUT , Cycle-to-Cycle Jitter , 72 MHz @ 5.0 VDC (Pin 6) – [...]

  • Page 10

    FS781/82/84 Document #: 38-07029 Rev . *F Page 10 of 12 Marking Example Package Drawing and Dimensions Cypress FS781BS Date Code, Lot # Cypress FS781BT Date Code, Lot # FS781 B S Cypress Device Driver Revision Package S = SOIC T = TSSOP SEATING PLANE P I N1I D 0.230[5.842] 0.244[6.197] 0.157[3.987] 0.150[3.810] 0.189[4.800] 0.196[4.978] 0.050[1.270[...]

  • Page 11

    FS781/82/84 Document #: 38-07029 Rev . *F Page 1 1 of 12 © Cypress Semi con duct or C orpo ra ti on , 20 05 . The i nfo r mat ion con t ained herein is subject to ch an ge wi t hou t notice. Cypress Semic onductor Corporation assu mes no responsib ility f or the u se of any circuitr y other than circ uitry embodied in a Cypress pr oduct. Nor does [...]

  • Page 12

    FS781/82/84 Document #: 38-07029 Rev . *F Page 12 of 12 Document History Page Document Title: FS781/82/84 Low EMI Spectrum Spread Clock Document Number: 38 -0702 9 REV . ECN NO. Issue Date Orig. of Change Description of Cha ng e ** 106948 06/07/01 IKA Convert from IMI to Cypress *A 1 1 1654 02/27/02 I KL Add new marking suffix for SOIC packages. Co[...]