WM8904ECSSLASHR datasheet(104/188 Pages) WOLFSON

104 / 188 page

WM8904

Pre-Production

PP, Rev 3.3, September 2012

104

The following operating frequency limits must be observed when configuring SYSCLK. Failure to

observe these limits will result in degraded noise performance and/or incorrect ADC/DAC

functionality.



SYSCLK

 3MHz



If DAC_OSR128 = 1 then SYSCLK

 6MHz



If DAC_MONO = 1, then SYSCLK

 64 x fs



If DAC_MONO = 0, then SYSCLK

 128 x fs



If ADCL_ENA = 1 or ADCR_ENA = 1 then SYSCLK

 256 x fs

Note that DAC Mono mode (DAC_MONO = 1) is only valid when one or other DAC is disabled. If both

DACs are enabled, then the minimum SYSCLK for clocking the DACs is 128 x fs.

The SYSCLK control register fields are defined in Table 61.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R22 (16h)

Clock Rates

MCLK_INV

MCLK Invert

0 = MCLK not inverted

1 = MCLK inverted

SYSCLK_SRC

SYSCLK Source Select

0 = MCLK

1 = FLL output

CLK_SYS_ENA

System Clock enable

0 = Disabled

1 = Enabled

R20 (14h)

Clock Rates

MCLK_DIV

Enables divide by 2 on MCLK

0 = SYSCLK = MCLK

1 = SYSCLK = MCLK / 2

Table 61 MCLK and SYSCLK Control

CONTROL INTERFACE CLOCKING

has been set to 1, then a Master Clock must be present for control register Read/Write operations. If

CLK_SYS_ENA = 1 and MCLK is not present, then register access will be unsuccessful. (Note that

read/write access to register R22, containing CLK_SYS_ENA, is always possible.)

If it cannot be assured that MCLK is present when accessing the register map, then it is required to

set CLK_SYS_ENA = 0 to ensure correct operation.

It is possible to use the WM8904 analogue bypass paths to the differential line outputs (LON/LOP and

RON/ROP) without MCLK. Note that MCLK is always required when using HPOUTL, HPOUTR,

LINEOUTL or LINEOUTR.

CLOCKING CONFIGURATION

The WM8904 supports a wide range of standard audio sample rates from 8kHz to 48kHz. The

Automatic Clocking Configuration simplifies the configuration of the clock dividers in the WM8904 by

deriving most of the necessary parameters from a minimum number of user registers.

The SAMPLE_RATE field selects the sample rate, fs, of the ADC and DAC. Note that the same

sample rate always applies to the ADC and DAC.

The CLK_SYS_RATE field must be set according to the ratio of SYSCLK to fs. When these fields are

set correctly, the Sample Rate Decoder circuit automatically determines the clocking configuration for

all other circuits within the WM8904.

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