WM8731SEDSSLASHV datasheet(41/65 Pages) WOLFSON

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WM8731 / WM8731L

Production Data

PD, Rev 4.9, October 2012

AUDIO DATA SAMPLING RATES

The WM8731/L provides for two modes of operation (normal and USB) to generate the required DAC

and ADC sampling rates. Normal and USB modes are programmed under software control according

to the table below.

In Normal mode, the user controls the sample rate by using an appropriate MCLK or crystal frequency

and the sample rate control register setting. The WM8731/L can support sample rates from 8ks/s up

to 96ks/s.

In USB mode, the user must use a fixed MLCK or crystal frequency of 12MHz to generate sample

rates from 8ks/s to 96ks/s. It is called USB mode since the common USB (Universal Serial Bus) clock

is at 12MHz and the WM8731/L can be directly used within such systems. WM8731/L can generate

all the normal audio sample rates from this one Master Clock frequency, removing the need for

different master clocks or PLL circuits.

Uniquely, the WM8731/L offers the user the ability to sample the ADC and DAC at different rates

under software control in both Normal and USB modes. This reduces the burden on any controlling

DSP. However, the signal processing in the ADC and DAC over-sampling filters is tightly coupled

together in order to minimise power consumption. To this end, only the combinations of sample rates

listed in the following sections are supported. Note that these rates supported are anticipated to be

the likely combinations used in typical audio systems.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0001000

Sampling

Control

USB/

NORMAL

Mode Select

1 = USB mode (250/272fs)

0 = Normal mode (256/384fs)

BOSR

Base Over-Sampling Rate

USB Mode

0 = 250fs

1 = 272fs

Normal Mode

96/88.2kHz

0 = 256fs

0 = 128fs

1 = 384fs

1 = 192fs

5:2

SR[3:0]

0000

ADC and DAC sample rate control;

See USB Mode and Normal Mode

Sample Rate sections for operation

Table 17 Sample Rate Control

NORMAL MODE SAMPLE RATES

In normal mode MCLK/crystal oscillator is set up according to the desired sample rates of the ADC

and DAC. For ADC or DAC sampling rates of 8, 32, 48 or 96kHz, MCLK frequencies of either

12.288MHz (256fs) or 18.432MHz (384fs) can be used. For ADC or DAC sampling rates of 8, 44.1 or

88.2kHz from MCLK frequencies of either 11.2896MHz (256fs) or 16.9344MHz (384fs) can be used.

Table 18 should be used to set up the device to work with the various sample rate combinations. For

example if the user wishes to use the WM8731/L in normal mode with the ADC and DAC sample

rates at 48kHz and 48kHz respectively then the device should be programmed with BOSR = 0, SR3 =

0, SR2 = 0, SR1 = 0 and SR0 = 0 with a 12.288MHz MCLK or with BOSR = 1, SR3 = 0, SR2 = 0, SR1

= 0 and SR0 = 0 with a 18.432MHz MCLK. The ADC and DAC will then operate with a Digital Filter of

type 1, refer to Digital Filter Characteristics section for an explanation of the different filter types.

WM8731SEDS/V 数据表(PDF) 41 Page - Wolfson Microelectronics plc

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