WM8912 datasheet(71/129 Pages) CIRRUS

71 / 129 page

Production Data

WM8912

PD, Rev 4.1, February 2013

In order to follow the above requirements for FVCO, the value of FLL_OUTDIV should be selected

according to the desired output FOUT. The divider, FLL_OUTDIV, must be set so that FVCO is in the

range 90-100MHz. The available divisions are integers from 4 to 64. Some typical settings of

FLL_OUTDIV are noted in Table 46.

OUTPUT FREQUENCY FOUT

FLL_OUTDIV

2.8125 MHz - 3.125 MHz

011111 (divide by 32)

3.75 MHz - 4.1667 MHz

011000 (divide by 24)

5.625 MHz - 6.25 MHz

001111 (divide by 16)

11.25 MHz - 12.5 MHz

000111 (divide by 8)

18 MHz - 20 MHz

000100 (divide by 5)

22.5 MHz - 25 MHz

000011 (divide by 4)

Table 46 Selection of FLL_OUTDIV

The value of FLL_FRATIO should be selected as described in Table 47.

REFERENCE FREQUENCY FREF

FLL_FRATIO

1MHz - 13.5MHz

0h (divide by 1)

256kHz - 1MHz

1h (divide by 2)

128kHz - 256kHz

2h (divide by 4)

64kHz - 128kHz

3h (divide by 8)

Less than 64kHz

4h (divide by 16)

Table 47 Selection of FLL_FRATIO

In order to determine the remaining FLL parameters, the FLL operating frequency, FVCO, must be

calculated, as given by the following equation:

FVCO = (FOUT x FLL_OUTDIV)

The value of FLL_N and FLL_K can then be determined as follows:

N.K = FVCO / (FLL_FRATIO x FREF)

See Table 48 for the coding of the FLL_OUTDIV and FLL_FRATIO fields.

Note that FREF is the input frequency, after division by FLL_CLK_REF_DIV, where applicable.

In FLL Fractional Mode, the fractional portion of the N.K multiplier is held in the FLL_K register field.

This field is coded as a fixed point quantity, where the MSB has a weighting of 0.5. Note that, if

desired, the value of this field may be calculated by multiplying K by 2

16 and treating FLL_K as an

integer value, as illustrated in the following example:

If N.K = 8.192, then K = 0.192

Multiplying K by 2

16 gives 0.192 x 65536 = 12582.912 (decimal)

Apply rounding to the nearest integer = 12583 (decimal) = 3127 (hex)

For best performance, FLL Fractional Mode should always be used. Therefore, if the calculations

yield an integer value of N.K, then it is recommended to adjust FLL_OUTDIV in order to obtain a non-

integer value of N.K. Care must always be taken to ensure that the FLL operating frequency, FVCO, is

within its recommended limits of 90-100 MHz.

The register fields that control the FLL are described in Table 48. Example settings for a variety of

reference frequencies and output frequencies are shown in Table 50.

WM8912 датащи(PDF) 71 Page - Cirrus Logic

WM8912 датащи(HTML) 71 Page - Cirrus Logic

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL