WM8580 datasheet(56/103 Pages) WOLFSON

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WM8580

Production Data

PD Rev 4.5 February 2008

PLL CONFIGURATION

The PLLs perform a configurable frequency multiplication of the input clock signal (f1). The

multiplication factor of the PLL (denoted by ‘R’) is variable and is defined by the relationship: R = (f2 ÷

f1).

The multiplication factor for each PLL is set using register bits PLLx_N and PLLx_K (refer to Table

47). The multiplication effect of both the N and K multipliers are additive (i.e. if N is configured to

provide a multiplication factor of 8 and K is configured to provide a multiplication factor of 0.192, the

overall multiplication factor is 8 + 0.192 = 8.192).

In order to choose and configure the correct values for PLLx_N and PLLx_K, multiplication factor R

must first be calculated. Once value R is calculated, the value of PLLx_N is the integer (whole

number) value of R, ignoring all digits to the right of the decimal point. For example, if R is calculated

to be 8.196523, PLL_N is simply 8.

Once PLLx_N is calculated, the PLLx_K value is simply the integer value of (222 (R-PLLx_N)). For

example, if R is 8.196523 and PLLx_N is 8, PLLx_K is therefore (222 (8.196523-8)), which is 824277

(ignoring all digits to the right of the decimal point).

Note:

The PLLs are designed to operate with best performance (shortest lock time and optimum stability)

when f2 is between 90 and 100MHz and PLLx_N is 8. However, acceptable PLLx_N values lie in the

range 5 ≤ PLLx_N ≤ 13.

Each PLL has an output divider to allow the f2 clock signal to be divided to a frequency suitable for

use as the source for the MCLK and CLKOUT outputs, the S/PDIF transmitter and the internal ADC

and DACs. The divider output is configurable and is set by the FREQMODE_A or FREQMODE_B

bits in conjunction with the POSTSCALE_A and POSTSCALE_B bits. Each PLL is also equipped

with a pre-scale divider which offers frequency divide by one or two before the OSCCLK signal is

input into the PLL. Please refer to Table 49 for details.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

PLLA 4

03h

PRESCALE_A

PLLB 4

07h

PRESCALE_B

PLL Pre-scale Divider Select

0 = Divide by 1 (PLL input clock =

oscillator clock)

1 = Divide by 2 (PLL input clock =

oscillator clock

÷ 2)

Note: PRESCALE_A must be set to

the same value as PRESCALE_B in

PLL S/PDIF receiver mode.

PLLA 4

03h

4:3

FREQMODE_A

[1:0]

PLLB 4

07h

4:3

FREQMODE_B

[1:0]

PLL Output Divider Select

PLL S/PDIF Receiver Mode

FREQMODE_A is automatically

controlled. FREQMODE_B is not

used.

PLL User Mode

Used in conjunction with the

POSTSCALE_x bits. Refer to Table

50.

PLLA 4

03h

POSTSCALE_A

PLLB 4

07h

POSTSCALE_B

PLL Post-scale Divider Select

PLL S/PDIF Receiver Mode

POSTSCALE_A is used to configure

a 256fs or 128fs PLLACLK,

POSTSCALE_B is not used. Refer

to Table 51.

PLL User Mode

Used in conjunction with the

FREQMODE_x bits. Refer to Table

50.

Table 49 Pre and Post PLL Clock Divider Control

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