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ICS84321 Folha de dados(PDF) 10 Page - Integrated Circuit Systems |
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ICS84321 Folha de dados(HTML) 10 Page - Integrated Circuit Systems |
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10 / 18 page ![]() 84321AY www.icst.com/products/hiperclocks.html REV. B JUNE 9, 2005 10 Integrated Circuit Systems, Inc. ICS84321 260MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER V CC - 2V 50 Ω 50 Ω RTT Z o = 50Ω Z o = 50Ω FOUT FIN RTT = Z o 1 ((V OH + VOL) / (VCC – 2)) – 2 3.3V 125 Ω 125 Ω 84 Ω 84 Ω Z o = 50Ω Z o = 50Ω FOUT FIN The clock layout topology shown below is a typical termina- tion for LVPECL outputs. The two different layouts mentioned are recommended only as guidelines. FOUT and nFOUT are low impedance follower outputs that generate ECL/LVPECL compatible outputs.Therefore, terminat- ing resistors (DC current path to ground) or current sources must be used for functionality. These outputs are designed to FIGURE 2B. LVPECL OUTPUT TERMINATION FIGURE 2A. LVPECL OUTPUT TERMINATION V CC - 2V drive 50 Ω transmission lines. Matched impedance techniques should be used to maximize operating frequency and minimize signal distortion. Figures 2A and 2B show two different layouts which are recommended only as guidelines. Other suitable clock layouts may exist and it would be recommended that the board designers simulate to guarantee compatibility across all printed circuit and clock component process variations. TERMINATION FOR LVPECL OUTPUTS APPLICATION INFORMATION CRYSTAL INPUT INTERFACE The ICS84321 has been characterized with 18pF parallel reso- nant crystals.The capacitor values shown in Figure 3 below were determined using a 25MHz, 18pF parallel resonant crystal and were chosen to minimize the ppm error. These same capacitor values will tune any 18pF parallel resonant crystal over the fre- quency range of 14MHz to 40MHz providing the other param- eters specified in Table 6, Crystal Characteristics, are satisfied. Figure 3. CRYSTAL INPUt INTERFACE C1 18p X1 18pF Parallel Crystal C2 22p XTAL_IN XTAL_OUT |
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