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AD9517-0 Datasheet(PDF) 36 Page - Analog Devices |
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AD9517-0 Datasheet(HTML) 36 Page - Analog Devices |
36 / 80 page AD9517-0 Data Sheet Rev. E | Page 36 of 80 By using combinations of the DM and FD modes, the AD9517 can achieve values of N all the way down to N = 1 and up to N = 26,2175. Table 28 shows how a 10 MHz reference input can be locked to any integer multiple of N. Note that the same value of N can be derived in different ways, as illustrated by the case of N = 12. The user can choose a fixed divide mode of P = 2 with B = 6; use the dual modulus mode of 2/3 with A = 0, B = 6; or use the dual modulus mode of 4/5 with A = 0, B = 3. The maximum frequency into the prescaler in 2/3 dual-modulus mode is limited to 200 MHz. There are only two cases where this frequency limitation limits the flexibility of that N divider: N = 7 and N = 11. In these two cases, the maximum frequency into the prescaler is 300 MHz and is achieved by using the P = 1 FD mode. In all other cases, the user can achieve the desired N divider value by using the other prescaler modes. A and B Counters The B counter must be ≥3 or bypassed, and, unlike the R counter, A = 0 is actually zero. When the prescaler is in dual-modulus mode, the A counter must be less than the B counter. The maximum input frequency to the A/B counter is reflected in the maximum prescaler output frequency (~300 MHz) that is specified in Table 2. This is the prescaler input frequency (VCO or CLK) divided by P. For example, a dual modulus mode of P = 8/9 is not allowed if the VCO frequency is greater than 2400 MHz because the frequency going to the A/B counter is too high. When the AD9517 B counter is bypassed (B = 1), the A counter should be set to 0, and the overall resulting divide is equal to the prescaler setting, P. The possible divide ratios in this mode are 1, 2, 3, 4, 8, 16, and 32. This mode is useful only when an external VCO/VCXO is used because the frequency range of the internal VCO requires an overall feedback divider greater than 32. Although manual reset is not normally required, the A/B counters have their own reset bit. Alternatively, the A and B counters can be reset using the shared reset bit of the R, A, and B counters. Note that these reset bits are not self-clearing. R, A, and B Counters—SYNC Pin Reset The R, A, and B counters can also be reset simultaneously through the SYNC pin. This function is controlled by Register 0x019[7:6] (see Table 54). The SYNC pin reset is disabled by default. R and N Divider Delays Both the R and N dividers feature a programmable delay cell. These delays can be enabled to allow adjustment of the phase relationship between the PLL reference clock and the VCO or CLK. Each delay is controlled by three bits. The total delay range is about 1 ns. See Register 0x019 in Table 54. Table 28. Using a 10 MHz Reference Input to Generate Different VCO Frequencies fREF (MHz) R P A B N fVCO (MHz) Mode Comments/Conditions 10 1 1 X 1 1 10 FD P = 1, B = 1 (A and B counters are bypassed). 10 1 2 X 1 2 20 FD P = 2, B = 1 (A and B counters are bypassed). 10 1 1 X 3 3 30 FD A counter is bypassed. 10 1 1 X 4 4 40 FD A counter is bypassed. 10 1 1 X 5 5 50 FD A counter is bypassed. 10 1 2 X 3 6 60 FD A counter is bypassed. 10 1 2 0 3 6 60 DM 10 1 2 1 3 7 70 DM Maximum frequency into prescaler in P = 2/3 mode is 200 MHz. If N = 7 or N = 11 is desired for prescaler input frequency of 200 MHz to 300 MHz, use P = 1, and N = 7 or 11, respectively. 10 1 2 2 3 8 80 DM 10 1 2 1 4 9 90 DM 10 1 8 6 18 150 1500 DM 10 1 8 7 18 151 1510 DM 10 1 16 7 9 151 1510 DM 10 10 32 6 47 1510 1510 DM 10 1 8 0 25 200 2000 DM 10 1 16 14 16 270 2700 DM P = 8 is not allowed (2700 ÷ 8 > 300 MHz). P = 32 is not allowed (A > B not allowed). 10 10 32 22 84 2710 2710 DM P = 32, A = 22, B = 84. P = 16 is also permitted. |
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