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CS2200-CP データシート(PDF) 11 Page - Cirrus Logic |
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CS2200-CP データシート(HTML) 11 Page - Cirrus Logic |
11 / 26 page CS2200-CP DS759PP1 11 5. APPLICATIONS 5.1 Timing Reference Clock Input The low jitter timing reference clock (RefClk) can be provided by either an external reference clock or an external crystal in conjunction with the internal oscillator. In order to maintain a stable and low-jitter PLL out- put the timing reference clock must also be stable and low-jitter; the quality of the timing reference clock directly affects the performance of the PLL and hence the quality of the PLL output. 5.1.1 Internal Timing Reference Clock Divider The Internal Timing Reference Clock (SysClk) has a smaller maximum frequency than what is allowed on the XTI/REF_CLK pin. The CS2200 supports the wider external frequency range by offering an internal divider for RefClk. The RefClkDiv[1:0] bits should be set such that SysClk, the divided RefClk, then falls within the valid range as indicated in Figure 5. It should be noted that the maximum allowable input frequency of the XTI/REF_CLK pin is dependent upon its configuration as either a crystal connection or external clock input. See the “AC Electrical Char- acteristics” on page 7 for more details. 5.1.2 Crystal Connections (XTI and XTO) An external crystal may be used to generate RefClk. To accomplish this, a 20 pF fundamental mode par- allel resonant crystal must be connected between the XTI and XTO pins as shown in Figure 6. As shown, nothing other than the crystal and its load capacitors should be connected to XTI and XTO. Please refer to the “AC Electrical Characteristics” on page 7 for the allowed crystal frequency range. Referenced Control Register Location RefClkDiv[1:0] ....................... “Reference Clock Input Divider (RefClkDiv[1:0])” on page 22 Figure 5. Internal Timing Reference Clock Divider N Internal Timing Reference Clock PLL Output Fractional-N Frequency Synthesizer Timing Reference Clock Divider ÷1 ÷2 ÷4 XTI/REF_CLK RefClkDiv[1:0] 8 MHz < SysClk < 18.75 MHz 8 MHz < RefClk < Timing Reference Clock 50 MHz (XTI) 75 MHz (REF_CLK) XTI XTO 40 pF 40 pF Figure 6. External Component Requirements for Crystal Circuit |
同様の部品番号 - CS2200-CP |
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同様の説明 - CS2200-CP |
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