WM8718

Production Data

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PD Rev 4.3 November 2006

14

DEVICE DESCRIPTION

INTRODUCTION

The WM8718 is a high performance DAC designed for digital consumer audio applications. Its

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

consumer audio equipment.

WM8718 is a complete 2-channel differential stereo audio digital-to-analogue converter, including

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

The WM8718 includes an on-chip digital volume control, configurable digital audio interface and a

3 wire MPU control interface. The WM8718 has left and right zero flag output pins, allowing the

user to control external muting circuits. It is fully compatible and an ideal partner for a range of

industry standard microprocessors, controllers and DSPs.

The software control interface may be asynchronous to the audio data interface. The control data

will be re-synchronised to the audio processing internally.

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

clock rates being automatically controlled. Sample rates (fs) from less than 8kHz to 192kHz are

allowed, provided the appropriate master clock is input. The audio data interface supports right

justified, left justified and I

highly flexible DSP serial port interface.

The device is packaged in a small 20-lead SSOP.

CLOCKING SCHEMES

In a typical digital audio system there is 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 system clock can be applied directly through the

MCLK input pin with no software configuration necessary for sample rate selection.

Note that on the WM8718, 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. Five popular

interface formats are supported:

•

Left Justified mode

•

Right Justified mode

•

I

•

DSP Mode A

•

DSP Mode B

All five formats send the MSB first and support word lengths of 16, 20, 24 and 32 bits with the

exception that 32 bit data is not supported in right justified mode.

DIN and LRCIN maybe

configured to be sampled on the rising or falling edge of BCKIN.

In left justified, right justified and I

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. 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.