WM8978CGEFLSLASHV datasheet(22/118 Pages) WOLFSON

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WM8978

Production Data

PD, Rev 4.5, October 2011

OUT3 and OUT4 can be configured to provide an additional stereo lineout from the output of the

DACs, the mixers or the input microphone boost stages. Alternatively OUT4 can be configured as a

mono mix of left and right DACs or mixers, or simply a buffered version of the chip midrail reference

voltage. OUT3 can also be configured as a buffered VMID output. This voltage may then be used as

a headphone ‘pseudo ground’ allowing removal of the large AC coupling capacitors often used in the

output path.

AUDIO INTERFACES

The WM8978 has a standard audio interface, to support the transmission of stereo data to and from

the chip. This interface is a 3 wire standard audio interface which supports a number of audio data

formats including I2S, DSP/PCM Mode (a burst mode in which LRC sync plus 2 data packed words

are transmitted), MSB-First, left justified and MSB-First, right justified, and can operate in master or

slave modes.

CONTROL INTERFACES

To allow full software control over all features, the WM8978 offers a choice of 2 or 3 wire control

interface. It is fully compatible and an ideal partner for a wide range of industry standard

microprocessors, controllers and DSPs.

Selection between the modes is via the MODE pin. In 2 wire mode the address of the device is fixed

as 0011010.

CLOCKING SCHEMES

WM8978 offers the normal audio DAC clocking scheme operation, where 256fs MCLK is provided to

the DAC and ADC.

A PLL is included which may be used to generate these clocks in the event that they are not available

from the system controller. This PLL uses an input clock, typically the 12MHz USB or ilink clock, to

generate high quality audio clocks. If this PLL is not required for generation of these clocks, it can be

reconfigured to generate alternative clocks which may then be output on the GPIO pins and used

elsewhere in the system.

POWER CONTROL

The design of the WM8978 has given much attention to power consumption without compromising

performance. It operates at very low voltages, and includes the ability to power off any unused parts

of the circuitry under software control, and includes standby and power off modes.

OPERATION SCENARIOS

Flexibility in the design of the WM8978 allows for a wide range of operational scenarios, some of

which are proposed below:

Multimedia phone; High quality playback to a stereo headset, a mono ear speaker or a loudspeaker is

supported, allowing hi-fi playback to be mixed with voice and other analogue inputs while

simultaneously transmitting a differential output from the microphone amplifier. A 5-band EQ enables

hi-fi playback to be customised to suit the user's preferences and the music style, while

programmable filtering allows fixed-frequency noise (e.g. 217Hz) to be reduced in the digital domain.

Stereo Camcorder; The provision of two stereo microphone preamplifiers, allows support for both

internal and external microphones. All drivers for speaker, headphone and line output connections are

integrated. The selectable ‘application filters’ after the ADC provide for features such as ‘wind noise’

reduction, or mechanical noise reducing filters.

Stereo Digital still camera recording; Support for digital stereo recording is similar to the camcorder

case. But additionally if the DSC supports MP3 playback, and perhaps recording, the ability of the

ADCs to support full 48ks/s high quality stereo recording increases device flexibility.

Mono Digital still camera; Full control over device functionality, and power control is provided,

allowing for the case of mono DSC recording, when half of the ADC and mic and line functionality

may be disabled to save power. In the mono case, the single ADC channel of audio data is sent out

over the Left channel of the audio interface.

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