WM8731L WOLFSON [Wolfson Microelectronics plc], WM8731L Datasheet - Page 30

• Manufacturer Part Number: WM8731L
• Description: Portable Internet Audio CODEC with Headphone Driver and Programmable Sample Rates
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

WM8731 / WM8731L
w
A zero cross detect circuit is provided at the input to the headphones under the control of the LZCEN
and RZCEN bits of the headphone output control register. Using these controls the volume control
values are only updated when the input signal to the gain stage is close to the analogue ground level.
This minimises and audible clicks and zipper noise as the gain values are changed or the device
muted. Note that this circuit has no time out so if only DC levels are being applied to the gain stage
input of more than approximately 20mV, then the gain will not be updated. This zero cross function is
enabled when the LZCEN and RZCEN bit is set high during a volume register write. If there is
concern that a DC level may have blocked a volume change (one made with LZCEN or RZCEN set
high) then a subsequent volume write of the same value, but with the LZCEN or RZCEN bit set low
will force a volume update, regardless of the DC level.
LHPOUT and RHPOUT volume and zero-cross setting can be changed independently. Alternatively,
the user can lock the two channels together, allowing both to be updated simultaneously, halving the
number of serial writes required, provided that the same gain is needed for both channels. This is
achieved through writing to the HPBOTH bit of the control register. Setting LRHPBOTH whilst writing
to LHPVOL and LZCEN will simultaneously update the Right Headphone controls similarly. The
corresponding effect on updating RLHPBOTH is also achieved.
The software control is given in Table 9.
Table 9 Headphone Output Software Control
0000010
Left
Headphone
Out
0000011
Right
Headphone
Out
REGISTER
ADDRESS
6:0
7
8
6:0
7
8
BIT
LHPVOL[6:0]
LZCEN
LRHPBOTH
RHPVOL[6:0]
RZCEN
RLHPBOTH
LABEL
1111001
( 0dB )
0
0
1111001
( 0dB )
0
0
DEFAULT
Left Channel Headphone Output
Volume Control
1111111 = +6dB
. . 1dB steps down to
0110000 = -73dB
0000000 to 0101111 = MUTE
Left Channel Zero Cross detect
Enable
1 = Enable
0 = Disable
Volume, Mute and Zero Cross Data
Load Control
1 = Enable Simultaneous Load of
LHPVOL[6:0] and LZCEN to
RHPVOL[6:0] and RZCEN
0 = Disable Simultaneous Load
Right Channel Headphone Output
Volume Control
1111111 = +6dB
. . 1dB steps down to
0110000 = -73dB
0000000 to 0101111 = MUTE
Right Channel Zero Cross Detect
Enable
1 = Enable
0 = Disable
Volume, Mute and Zero Cross Data
Load Control
1 = Enable Simultaneous Load of
RHPVOL[6:0] and RZCEN to
LHPVOL[6:0] and LZCEN
0 = Disable Simultaneous Load
Left to Right Channel Headphone
Right to Left Channel Headphone
DESCRIPTION
PD Rev 4.3 August 2006
Production Data
30