WM8776 datasheet(13/55 Pages) WOLFSON

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WM8776

PP Rev 1.91 June 2004

DEVICE DESCRIPTION

INTRODUCTION

WM8776 is a complete 2-channel DAC, 2-channel ADC audio codec, with flexible input

multiplexor including digital interpolation and decimation filters, multi-bit sigma delta stereo

ADC, and switched capacitor multi-bit sigma delta DACs with analogue volume controls on

each channel and output smoothing filters. It is available in a single package and controlled

by either a 3-wire or 2-wire software interface. The 3-wire interface is compatible with the SPI

standard.

An analogue bypass path option is available, to allow stereo analogue signals from any of the

5 stereo inputs to be sent to the stereo outputs via the main volume controls. This allows a

purely analogue input to analogue output high quality signal path to be implemented if

required.

The DAC and ADC have separate left/right clocks, bit clocks, master clocks and data I/Os.

The Audio Interface may be configured to operate in either master or slave mode. In Slave

mode ADCLRC, DACLRC, ADCBCLK and DACBCLK are all inputs. In Master mode

ADCLRC, DACLRC, ADCBCLK and DACBCLK are outputs.

The input multiplexor to the ADC is configured to allow large signal levels to be input to the

ADC, using external resistors to reduce the amplitude of larger signals to within the normal

operating range of the ADC. The ADC has an analogue input PGA and a digital gain control,

accessed by one register write. The input PGA allows input signals to be gained up to +24dB

and attenuated down to -21dB in 0.5dB steps. The digital gain control allows attenuation from

-21.5dB to -103dB in 0.5dB steps. This allows the user maximum flexibility in the use of the

ADC.

The DAC has its own digital volume control, which is adjustable between 0dB and -127.5dB

in 0.5dB steps. There is also an analogue volume control on the headphone outputs, which is

adjustable between +6dB and -73dB in 1dB steps. The analogue and digital volume controls

may be operated independently. In addition a zero cross detect circuit is provided for both

analogue and digital volume controls. When analogue volume zero-cross detection is

enabled the attenuation values are only updated when the input signal to the gain stage is

close to the analogue ground level. The digital volume control detects a transition through the

zero point before updating the volume. This minimises audible clicks and ‘zipper’ noise as

the gain values change.

The DAC output incorporates an input selector and mixer allowing a signal to be either

switched into the signal path in place of the DAC signal or mixed with the DAC signal before

the volume control. Use of external resistors allows larger input levels to be accepted by the

device, giving maximum user flexibility.

Internal functionality is controlled by CE, CL, DI and MODE input pins. These are 5V tolerant

with TTL input thresholds, allowing the WM8776 to used with DVDD = 3.3V and be controlled

by a controller with 5V output. The MODE pin determines which of the two control interface

modes is selected.

Operation using system clock of 128fs, 192fs, 256fs, 384fs, 512fs or 768fs is provided. In

Slave mode selection between clock rates is automatically controlled. In master mode the

master clock to sample rate ratio is set by control bits ADCRATE and DACRATE. ADC and

DAC may run at different rates and have their own bit clocks and master clocks.

The audio data interface supports right, left and I

2S interface formats along with a highly

flexible DSP serial port interface.

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