WM8974 datasheet(36/63 Pages) WOLFSON

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WM8974

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PP Rev 1.1 September 2004

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

DAC2MONO

Output of DAC to mono mixer input

0 = not selected

1 = selected

BYP2MONO

Bypass path (output of input boost

stage) to mono mixer input

0 = non selected

1 = selected

AUX2MONO

Output of Auxillary amplifier to mono

mixer input:

0 = not selected

1 = selected

R56

Mono mixer

control

MONOMUTE

0=No mute

1=Output muted. During mute the

mono output will output VMID which can

be used as a DC reference for a

headphone out.

Table 24 Mono Mixer Control

ENABLING THE OUTPUTS

Each analogue output of the WM8974 can be separately enabled or disabled. The analogue mixer

associated with each output has a separate enable. All outputs are disabled by default. To save

power, unused parts of the WM8974 should remain disabled.

Outputs can be enabled at any time, but it is not recommended to do so when BUFIO is disabled

(BUFIOEN=0), as this may cause pop noise (see “Power Management” and “Applications

Information” sections).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

BUFIOEN

Unused input/output tie off buffer enable

Power

management 1

BUFDCOPEN 0

Output stage 1.5xAVDD/2 driver enable

SPKMIXEN

Speaker Mixer enable

MONOMIXEN 0

Mono mixer enable

SPKPEN

SPKROUTP enable

SPKNEN

SPKROUTN enable

Power

management 3

MONOEN

MONOOUT enable

Note: All “Enable” bits are 1 = ON, 0 = OFF

Table 25 Output Stages Power Management Control

UNUSED ANALOGUE INPUTS/OUTPUTS

Whenever an analogue input/output is disabled, it remains connected to a voltage source (either

AVDD/2 or 1.5xAVDD/2 as appropriate) through a resistor. This helps to prevent pop noise when the

output is re-enabled. The resistance between the voltage buffer and the output pins can be

controlled using the VROI contol bit. The default impedance is low, so that any capacitors on the

outputs can charge up quickly at start-up. If a high impedance is desired for disabled outputs, VROI

can then be set to 1, increasing the resistance to about 30k

Ω.

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