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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