WM8978GEFLSLASHV datasheet(44/78 Pages) WOLFSON

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WM8978

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PP Rev 1.7 January 2005

Figure 17 Speaker Outputs LOUT2 and ROUT2

The signal to be output on LOUT2/ROUT2 comes from the Left/Right Mixer circuits and can be any

combination of the DAC output, the Bypass path (output of the input boost stage) and the AUX input.

The LOUT2/ROUT2 volume is controlled by the LOUT2VOL/ ROUT2VOL register bits. Note that

gains over 0dB may cause clipping if the signal is large. The LOUT2MUTE/ ROUT2MUTE register

bits cause the speaker outputs to be muted (the output DC level is driven out). The output pins

remain at the same DC level (DCOP), so that no click noise is produced when muting or un-muting

The speaker output stages also have a selectable gain boost of 1.5x (3.52dB). When this boost is

enabled the output DC level is also level shifted (from AVDD/2 to 1.5xAVDD/2) to prevent the signal

from clipping. A dedicated amplifier BUFDCOP, as shown in Figure 18, is used to perform the DC

level shift operation.

This buffer must be enabled using the BUFDCOPEN register bit for this

operating mode. It should also be noted that if SPKVDD is not equal to or greater than 1.5xAVDD

this boost mode may result in signals clipping. Table 33 summarises the effect of the SPKBOOST

control bits.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R49

Output control

SPKBOOST

0 = Speaker gain = -1;

DC = AVDD / 2

1 = Speaker gain = +1.5;

DC = 1.5 x AVDD / 2

Power

management

BUFDCOPEN

Dedicated buffer for DC level shifting

output stages when in 1.5x gain

boost configuration.

0=Buffer disabled

1=Buffer enabled (required for 1.5x

gain boost)

Table 32 Speaker Boost Stage Control

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