WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 56

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WM8978

Manufacturer Part Number
WM8978
Description
The WM8978 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
Manufacturer
Wolfson Microelectronics Ltd.
Datasheet

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WM8978
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Table 36 Speaker Volume Control
The signal 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. 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 27, is used to perform the DC
level shift operation.
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 38 summarises the effect of the SPKBOOST
control bits.
R54
LOUT2 (SPK)
Volume
control
R55
ROUT2 (SPK)
Volume
control
REGISTER
ADDRESS
7
6
5:0
8
7
6
5:0
8
BIT
This buffer must be enabled using the BUFDCOPEN register bit for this
LOUT2ZC
LOUT2MUTE
LOUT2VOL
SPKVU
ROUT2ZC
ROUT2MUTE
ROUT2VOL
SPKVU
LABEL
Not latched
Not latched
DEFAULT
111001
111001
0
0
0
0
Speaker volume zero cross enable:
1 = Change gain on zero cross only
0 = Change gain immediately
Left speaker output mute:
0 = Normal operation
1 = Mute
000000 = -57dB
...
111001 = 0dB
...
111111 = +6dB
LOUT2 and ROUT2 volumes do not
update until a 1 is written to SPKVU
(in reg 54 or 55)
Speaker volume zero cross enable:
1 = Change gain on zero cross only
0 = Change gain immediately
Right speaker output mute:
0 = Normal operation
1 = Mute
Right speaker output volume:
000000 = -57dB
...
111001 = 0dB
...
111111 = +6dB
LOUT2 and ROUT2 volumes do not
update until a 1 is written to SPKVU
(in reg 54 or 55)
Left speaker output volume:
PTD Rev 2.6 November 2005
DESCRIPTION
Preliminary Technical Data
56