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CPLL Datasheet(PDF) 18 Page - Exar Corporation |
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CPLL Datasheet(HTML) 18 Page - Exar Corporation |
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18 / 29 page  X XR RP P7 77 72 24 4 Q Qu ua ad d C Ch ha an nn ne ell D Diig giitta all P PW WM M/ /P PF FM M P Prro og grra am mm ma ab blle e P Po ow we err M Ma an na ag ge em me en ntt S Sy ys stte em m © 2012 Exar Corporation 18/29 Rev. 1.0.1 Figure 18 shows a simplified block diagram of the XRP7724 timings. Again, please note that the function blocks and signal names used are chosen for ease of understanding and do not necessarily reflect the actual design. The system timings are generated by a 103MHz internal system clock (Sys_Clk). There are two ways that the 103 MHz system clock can be generated. These include an internal oscillator and a Phase Locked Loop (PLL) that is synchronized to an external clock input. The basic timing architecture is to divide the Sys_Clk down to create a fundamental switching frequency (Fsw_Fund) for all the output channels that is settable from 105kHz to 306kHz. The switching frequency for a channel (Fsw_CHx) can then be selected as 1 times, 2 times or 4 times the fundamental switching frequency. To set the base frequency for the output channels a “Fsw_Set” value representing the base frequency shown in Table 1, is entered into the switching frequency configuration register (Fsw_Set is basically equal to the base frequency times 256). The system timings are then created by dividing down Sys_Clk to produce a base frequency clock, 2X and 4X times the base frequency clocks, and sequencing timing to position the output channels relative to each other. Each output channel then has its own frequency multiplier register that is used to select its final output switching frequency. Table 1 shows the available channel switching frequencies for the XRP7724 device. In practice the PowerArchitect™ 5.0 design tool handles all the details and the user only has to enter the fundamental switching frequency and the 1x, 2x, 4x frequency multiplier for each channel. If an external clock is used, the frequencies in this table will shift accordingly. Base Frequency kHz Available 2x Frequencies kHz Available 4x Frequencies kHz 105.5 211.1 422.1 107.3 214.6 429.2 109.1 218.2 436.4 111.0 222.0 444.0 112.9 225.9 451.8 115.0 229.9 459.8 117.0 234.1 468.2 119.2 238.4 476.9 121.5 242.9 485.8 123.8 247.6 495.2 126.2 252.5 504.9 128.8 257.5 515.0 131.4 262.8 525.5 134.1 268.2 536.5 137.0 273.9 547.9 139.9 279.9 559.8 143.1 286.1 572.2 146.3 292.6 585.2 149.7 299.4 598.8 153.3 306.5 613.1 157.0 314.0 628.0 160.9 321.9 643.8 165.1 330.1 660.3 169.4 338.8 677.6 174.0 348.0 695.9 178.8 357.6 715.3 183.9 367.9 735.7 189.3 378.7 757.4 195.1 390.2 780.3 201.2 402.3 804.7 207.7 415.3 830.6 214.6 429.2 858.3 222.0 444.0 887.9 229.9 459.8 919.6 238.4 476.9 953.7 247.6 495.2 990.4 257.5 515.0 1030.0 268.2 536.5 1072.9 279.9 559.8 1119.6 292.6 585.2 1170.5 306.5 613.1 1226.2 Table 1 |
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