WM8978CGEFLSLASHV datasheet(83/118 Pages) WOLFSON

83 / 118 page

Production Data

WM8978

PD, Rev 4.5, October 2011

In 2-wire mode the WM8978 has a fixed device address, 0011010.

RESETTING THE CHIP

The WM8978 can be reset by performing a write of any value to the software reset register (address

0 hex). This will cause all register values to be reset to their default values. In addition to this there

is a Power-On Reset (POR) circuit which ensures that the registers are set to default when the device

is powered up.

POWER SUPPLIES

The WM8978 can use up to five separate power supplies:

AVDD and AGND: Analogue supply, powers all analogue functions except the speaker output and

mono output drivers. AVDD can range from 2.5V to 3.6V and has the most significant impact on

overall power consumption (except for power consumed in the headphone). A large AVDD slightly

improves audio quality.

SPKVDD and SPKGND: Headphone and Speaker supplies, power the speaker and mono output

drivers. SPKVDD can range from 2.5V to 5V. SPKVDD can be tied to AVDD, but it requires separate

layout and decoupling capacitors to curb harmonic distortion. With a larger SPKVDD, louder

headphone and speaker outputs can be achieved with lower distortion. If SPKVDD is lower than

AVDD, the output signal may be clipped.

DCVDD: Digital core supply, powers all digital functions except the audio and control interfaces.

DCVDD can range from 1.71V to 3.6V, and has no effect on audio quality. The return path for

DCVDD is DGND, which is shared with DBVDD.

DBVDD can range from 1.71V to 3.6V. DBVDD return path is through DGND.

It is possible to use the same supply voltage for all four supplies. However, digital and analogue

supplies should be routed and decoupled separately on the PCB to keep digital switching noise out of

the analogue signal paths.

DCVDD should be greater than or equal to 1.9V when using the PLL.

RECOMMENDED POWER UP/DOWN SEQUENCE

In order to minimise output pop and click noise, it is recommended that the WM8978 device is

powered up and down using one of the following sequences:

Power-up when NOT using the output 1.5x boost stage:

Turn on external power supplies. Wait for supply voltage to settle.

Mute all analogue outputs.

Set L/RMIXEN = 1 and DACENL/R = 1 in register R3.

Set BUFIOEN = 1 and VMIDSEL[1:0] to required value in register R1. Wait for the VMID supply

to settle. *Refer notes 1 and 2.

Set BIASEN = 1 in register R1.

Set L/ROUT1EN = 1 in register R2.

Enable other mixers as required.

Enable other outputs as required.

Set remaining registers.

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