Pre-Production
WM8904
The FLL output frequency is generated according to the following equation:
OUT = (FVCO / FLL_OUTDIV)
F
The FLL operating frequency, FVCO is set according to the following equation:
FVCO = (FREF x N.K x FLL_FRATIO)
See Table 71 for the coding of the FLL_OUTDIV and FLL_FRATIO fields.
F
REF is the input frequency, as determined by FLL_CLK_REF_DIV.
VCO must be in the range 90-100 MHz. Frequencies outside this range cannot be supported.
F
Note that the output frequencies that do not lie within the ranges quoted above cannot be guaranteed
across the full range of device operating temperatures.
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 69.
OUTPUT FREQUENCY FOUT
2.8125 MHz - 3.125 MHz
3.75 MHz - 4.1667 MHz
5.625 MHz - 6.25 MHz
FLL_OUTDIV
011111 (divide by 32)
011000 (divide by 24)
001111 (divide by 16)
000111 (divide by 8)
000100 (divide by 5)
000011 (divide by 4)
11.25 MHz - 12.5 MHz
18 MHz - 20 MHz
22.5 MHz - 25 MHz
Table 69 Selection of FLL_OUTDIV
The value of FLL_FRATIO should be selected as described in Table 70.
REFERENCE FREQUENCY FREF
1MHz - 13.5MHz
FLL_FRATIO
0h (divide by 1)
256kHz - 1MHz
1h (divide by 2)
2h (divide by 4)
3h (divide by 8)
4h (divide by 16)
128kHz - 256kHz
64kHz - 128kHz
Less than 64kHz
Table 70 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 71 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.
PP, Rev 3.3, September 2012
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
