WM8978GEFLSLASHV datasheet(65/78 Pages) WOLFSON

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WM8978

PP Rev 1.7 January 2005

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 1.62V 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 1.8V 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.

RECOMMENDED POWER UP/DOWN SEQENCE

In order to minimise output ‘pop’ and ‘click’ noise it is recommended that the device is powered up in

a controlled sequence.

In addition to this it is recommended that the zero cross functions are used when changing the

volume in the PGAs.

POWER MANAGEMENT

SAVING POWER BY REDUCING OVERSAMPLING RATE

The default mode of operation of the ADC and DAC digital filters is in 64x oversampling mode.

Under the control of ADCOSR and DACOSR the oversampling rate may be doubled. 64x

oversampling results in a slight decrease in noise performance compared to 128x but lowers the

power consumption of the device.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R10

DAC control

DACOSR128

DAC oversample rate select

0 = 64x (lowest power)

1 = 128x (best SNR)

R14

ADC control

ADCOSR128

ADC oversample rate select

0 = 64x (lowest power)

1 = 128x (best SNR)

Table 55 ADC and DAC Oversampling Rate Selection

VMID

The analogue will not work unless VMID is enabled (VMIDSEL 00). The impedance of the VMID

resistor string, together with the decoupling capacitor on the VMID pin will determine the startup time

of the VMID circuit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Power

management 1

1:0

VMIDSEL

Reference string impedance to VMID pin

(detemines startup time):

00=off (open circuit)

01=75kΩ

10=300kΩ

11=5kΩ (for fastest startup)

Table 56 VMID Impedance Control

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