WM8352
Production Data
12.4.1 EXAMPLE FLL CALCULATION
To generate 12.288 MHz output (FOUT) from a 12.000 MHz reference clock (FREF):
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Determine FLL_OUTDIV for the required output frequency as given by Table 16:
For FOUT = 12.288 MHz, FLL_OUTDIV = 2h (divide by 8)
Calculate FVCO for the given FLL_OUTDIV:
F
VCO = FOUT * FLL_OUTDIV = 12.288 MHz * 8 = 98.304 MHz
Calculate the required N.K x FLL_RATIO for the given FREF and FVCO.:
N.K x FLL_RATIO = FVCO / FREF = 8.192
Determine FLL_REF_FREQ for the given FREF as given by Table 17:
For FREF = 12MHz, FLL_REF_FREQ = 0
Determine FLL_RATIO as given by Table 17:
For High Frequency Reference, FLL_RATIO = 1
Calculate N.K for the given FLL_RATIO:
N.K = 8.192 / 1 = 8.192
Determine FLL_N and FLL_K from the integer and fractional portions of N.K:
FLL_N is 8. FLL_K is 0.192
Set FLL_FRAC according to whether fractional mode is required:
FLL_K is 0.192, so fractional mode is required; FLL_FRAC = 1
Note that, for best performance, FLL Fractional Mode should always be used. If the calculations yield
an integer value of N.K, then it is recommended to adjust FLL_RATIO in order to obtain a non-integer
value of N.K.
PD, February 2011, Rev 4.4
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