WM8739LEDS datasheet(20/35 Pages) WOLFSON

20 / 35 page

WM8739 / WM8739L

Advanced Information

AI Rev 2.2 September 2001

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0USB/

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

0 = 256fs

1 = 384fs

0001000

Sampling

Control

5:2

SR[3:0]

0000

ADC sample rate control;

See USB Mode and Normal Mode

Sample Rate sections for operation

Table 7 Sample Rate Control

NORMAL MODE SAMPLE RATES

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

For ADC sampling rates of 8, 32, 48 or 96KHz, MCLK frequencies of either 12.288MHz (256fs) or

18.432MHz (384fs) can be used. For ADC sampling rates of 8, 44.1 or 88.2KHz from MCLK

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

The table below 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 WM8739 in normal mode with the ADC

sample rate at 48KHz, 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 will then operate with a Digital Filter of type 1, refer to

Digital Filter Characteristics section for an explanation of the different filter types.

SAMPLING

RATE

MCLK

FREQUENCY

SAMPLE

RATE

DIGITAL

FILTER

TYPE

kHz

MHz

BOSR

SR3

SR2

SR1

SR0

12.288

18.432

12.288

18.432

12.288

18.432

12.288

18.432

11.2896

44.1

16.9344

11.2896

8 (Note 1)

16.9344

11.2896

88.2

16.9344

Table 8 Normal Mode Sample Rate Look-up Table

Notes:

8k not exact, actual = 8.018kHz

All other combinations of BOSR and SR[3:0] that are not in the truth table are invalid

The BOSR bit represents the base over-sampling rate. This is the rate that the WM8739 digital signal

processing is carried out at. In Normal mode, with BOSR = 0, the base over-sampling rate is at

256fs, with BOSR = 1, the base over-sampling rate is at 384fs. This can be used to determine the

actual audio data rate produced by the ADC.

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