WM8945ECSSLASHR datasheet(78/169 Pages) WOLFSON

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WM8945

Production Data

PD, May 2011, Rev 4.1

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R9 (09h)

FLL Control 2

15:0

FLL_K[15:0]

3137h

Fractional multiply for FREF

(MSB = 0.5)

R10 (0Ah)

FLL Control 3

14:5

FLL_N[9:0]

008h

Integer multiply for FREF

(LSB = 1)

3:0

FLL_GAIN

[3:0]

0100

Gain applied to error

0000 = x 1 (Recommended value)

0001 = x 2

0010 = x 4

0011 = x 8

0100 = x 16

0101 = x 32

0110 = x 64

0111 = x 128

1000 = x 256

Recommended that this register is set

0000.

Table 53 Frequency Locked Loop Control

EXAMPLE FLL CALCULATION

To generate 24.576MHz output (FOUT) from a 12.000MHz reference clock (FREF):



Set FLL_CLK_REF_DIV in order to generate FREF <=13.5MHz:

FLL_CLK_REF_DIV = 00 (divide by 1)



Set FLL_CTRL_RATE to the recommended setting:

FLL_CTRL_RATE = 000 (divide by 1)



Sett FLL_GAIN to the recommended setting:

FLL_GAIN = 0000 (multiply by 1)



Set FLL_OUTDIV for the required output frequency as shown in Table 51:-

FOUT = 24.576MHz, therefore FLL_OUTDIV = 1h (divide by 4)



Set FLL_FRATIO for the given reference frequency as shown in Table 52:

FREF = 12MHz, therefore FLL_FRATIO = 0h (divide by 1)



Calculate FVCO as given by FVCO = FOUT x FLL_OUTDIV:-

FVCO = 24.576 x 4 = 98.304MHz



Calculate N.K as given by N.K = FVCO / (FLL_FRATIO x FREF):

N.K = 98.304 / (1 x 12) = 8.192



Determine FLL_N and FLL_K from the integer and fractional portions of N.K:-

FLL_N is 8(dec) = 008(hex). FLL_K is 0.192 (dec) = 3127(hex).



Confirm that N.K is a fractional quantity and set FLL_FRAC:

N.K is fractional. Set FLL_FRAC = 1.

Note that, if N.K is an integer, then an alternative value of FLL_FRATIO may be selected in

order to produce a fractional value of N.K.

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