WM8729 Просмотр технического описания (PDF) - Wolfson Microelectronics plc

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WM8729

24-bit, 192kHz Stereo DAC

Wolfson Microelectronics plc 

WM8729

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DEVICE DESCRIPTION

INTRODUCTION

The WM8729 is a high performance DAC designed for digital consumer audio applications. Its

range of features make it ideally suited for use in DVD players, AV receivers and other high end

consumer audio equipment.

The WM8729 is a complete 2-channel stereo audio digital-to-analogue converter, including digital

interpolation filter, multi-bit sigma delta with dither, and switched capacitor multi-bit stereo DAC

and output smoothing filters. It is fully compatible and an ideal partner for a range of industry

standard microprocessors, controllers and DSPs.

Control of internal functionality of the device is provided by hardware control (pin programmed).

Operation using master clocks of 256fs, 384fs, 512fs or 768fs is provided, selection between

clock rates being automatically controlled. Sample rates (fs) from less than 8ks/s to 96ks/s are

allowed, provided the appropriate system clock is input. Support is also provided for up to 192ks/s

using a master clock of 128fs or 192fs.

The audio data interface supports right justified or I2S (Philips left justified, one bit delayed)

interface formats.

The device is packaged in a small 16-pin SOIC.

CLOCKING SCHEMES

In a typical digital audio system there is only one central clock source producing a reference clock

to which all audio data processing is synchronised. This clock is often referred to as the audio

system’s Master Clock. The external master clock can be applied directly through the MCLK input

pin with no configuration necessary for sample rate selection.

Note that on the WM8729, MCLK is used to derive clocks for the DAC path. The DAC path

consists of DAC sampling clock, DAC digital filter clock and DAC digital audio interface timing. In

a system where there are a number of possible sources for the reference clock it is recommended

that the clock source with the lowest jitter be used to optimise the performance of the DAC.

DIGITAL AUDIO INTERFACE

Audio data is applied to the internal DAC filters via the Digital Audio Interface. Two popular

interface formats are supported:

Right Justified mode

I2S mode

Both formats send the MSB first. The WM8729 supports word lengths of 16 or 24 bits in I2S

mode and 16 or 20 bits in right justified mode. In right justified and I2S modes, the digital audio

interface receives data on the DIN input. Audio Data is time multiplexed with LRCIN indicating

whether the left or right channel is present. LRCIN is also used as a timing reference to indicate

the beginning or end of the data words.

In right justified and I2S modes, the minimum number of BCKINs per LRCIN period is 2 times the

selected word length. LRCIN must be high for a minimum of word length BCKINs and low for a

minimum of word length BCKINs. Any mark to space ratio on LRCIN is acceptable provided the

above requirements are met.

WOLFSON MICROELECTRONICS LTD

PP Rev 1.2 April 2001

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