WM1811A datasheet(192/328 Pages) WOLFSON

192 / 328 page

WM1811A

Production Data

PD, November 2013, Rev 4.1

192

In Fractional Mode (FLLn_THETA > 0 and FLLn_EFS_ENA = 1), the register fields FLLn_THETA and

FLLn_LAMBDA can be calculated as follows:

Calculate GCD(FLL) using the ‘Greatest Common Denominator’ function:

GCD(FLL) = GCD(FLLn_FRATIO x FREF, FVCO)

where GCD(x, y) is the greatest common denominator of x and y

Next, calculate FLLn_THETA and FLLn_LAMBDA using the following equations:

FLLn_THETA = (FVCO - (FLLn_N x FLLn_FRATIO x FREF)) / GCD(FLL)

FLLn_LAMBDA = (FLLn_FRATIO x FREF) / GCD(FLL)

Note that, in Fractional Mode, the values of FLLn_THETA and FLLn_LAMBDA must be co-prime (ie.

not divisible by any common integer). The calculation above ensures that the values will be co-prime.

The value of K must be a fraction less than 1 (ie. FLLn_THETA must be less than FLLn_LAMBDA).

The FLL1 control registers are described in Table 115. The FLL2 control registers are described in

Table 116. Example settings for a variety of reference frequencies and output frequencies are shown

in Table 118.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R544 (0220h)

FLL1 Control (1)

FLL1_ENA

FLL1 Enable

0 = Disabled

1 = Enabled

This should be set as the final step of

the FLL1 enable sequence, ie. after

the other FLL registers have been

configured.

R545 (0221h)

FLL1 Control (2)

13:8

FLL1_OUTDIV

[5:0]

000000

FLL1 FOUT clock divider

000000 = Reserved

000001 = Reserved

000010 = Reserved

000011 = 4

000100 = 5

000101 = 6

…

111110 = 63

111111 = 64

(FOUT = FVCO / FLL1_OUTDIV)

2:0

FLL1_FRATIO

[2:0]

000

FLL1 FVCO clock divider

000 = 1

001 = 2

010 = 4

011 = 8

1XX = 16

R546 (0222h)

FLL1 Control (3)

15:0

FLL1_THETA[15

:0]

0000h

FLL Fractional multiply for FREF

This field sets the numerator

(multiply) part of the FLL1_THETA /

FLL1_LAMBDA ratio.

Coded as LSB = 1.

R547 (0223h)

FLL1 Control (4)

14:5

FLL1_N[9:0]

000h

FLL Integer multiply for FREF

(LSB = 1)

WM1811A Datasheet(PDF) 192 Page - Wolfson Microelectronics plc

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