WM5102 datasheet(241/334 Pages) WOLFSON

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Production Data

WM5102

PD, June 2014, Rev 4.2

241

In Fractional Mode (FLLn_THETA > 0), the register fields FLLn_THETA and FLLn_LAMBDA can be

calculated as described below.

Note that an equivalent procedure is also used to derive the FLLn_SYNC_THETA and

FLLn_SYNC_LAMBDA register values from the corresponding synchroniser parameters.

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

FREF is the input frequency, after division by FLLn_REFCLK_DIV, where applicable.

Next, calculate FLLn_THETA and FLLn_LAMBDA using the following equations:

FLLn_THETA = (FVCO - (FLL_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 FLL control registers are described in Table 104 and Table 105. Example settings for a variety of

reference frequencies and output frequencies are shown in Table 108.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R369

(0171h)

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.

R370

(0172h)

FLL1

Control 2

FLL1_CTRL_UP

FLL1 Control Update

Write ‘1’ to apply the FLL1_N and

FLL1_THETA register settings.

(Only valid when FLL1_ENA=1)

9:0

FLL1_N [9:0]

008h

FLL1 Integer multiply for FREF

(LSB = 1)

If updated while the FLL is enabled, the

new value is only effective when a ‘1’ is

written to FLL1_CTRL_UPD.

R371

(0173h)

FLL1

Control 3

15:0

FLL1_THETA

[15:0]

0018h

FLL1 Fractional multiply for FREF

This field sets the numerator (multiply)

part of the FLL1_THETA / FLL1_LAMBDA

ratio.

Coded as LSB = 1.

If updated while the FLL is enabled, the

new value is only effective when a ‘1’ is

written to FLL1_CTRL_UPD.

R372

(0174h)

FLL1

Control 4

15:0

FLL1_LAMBDA

[15:0]

007Dh

FLL1 Fractional multiply for FREF

This field sets the denominator (dividing)

part of the FLL1_THETA / FLL1_LAMBDA

ratio.

Coded as LSB = 1.

WM5102 Datasheet(PDF) 241 Page - Wolfson Microelectronics plc

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