WM8904 Datasheet, PDF (88/188 Pages) Wolfson Microelectronics plc – Ultra Low Power CODEC for Portable Audio Applications

WM8904
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
Pre-Production
DESCRIPTION
7:4 DCS_DAC_WR_C
OMPLETE [3:0]
0000
DC Servo DAC Write status
[3] - LINEOUTR
[2] - LINEOUTL
[1] - HPOUTR
[0] - HPOUTL
3:0 DCS_STARTUP_
COMPLETE [3:0]
0000
0 = DAC Write DC Servo mode not
completed.
1 = DAC Write DC Servo mode
complete.
DC Servo Start-Up status
[3] - LINEOUTR
[2] - LINEOUTL
[1] - HPOUTR
[0] - HPOUTL
Table 52 DC Servo Enable and Start-Up Modes
0 = Start-Up DC Servo mode not
completed..
1 = Start-Up DC Servo mode
complete.
DC SERVO ACTIVE MODES
The DC Servo modes described above are suitable for initialising the DC offset correction circuit on
the Line and Headphone outputs as part of a controlled start-up sequence which is executed before
the signal path is fully enabled. Additional modes are available for use whilst the signal path is active;
these modes may be of benefit following a large change in signal gain, which can lead to a change in
DC offset level. Periodic updates may also be desirable to remove slow drifts in DC offset caused by
changes in parameters such as device temperature.
The DC Servo circuit is enabled on HPOUTR and HPOUTL by setting DCS_ENA_CHAN_1 and
DCS_ENA_CHAN_0 respectively, as described earlier in Table 52. Similarly, the DC Servo circuit is
enabled on LINEOUTR and LINEOUTL by setting DCS_ENA_CHAN_3 and DCS_ENA_CHAN_2
respectively.
Writing a logic 1 to DCS_TRIG_SINGLE_n initiates a single DC offset measurement and adjustment
to the associated output; (‘n’ = 3 for LINEOUTR channel, 2 for LINEOUTL channel, 1 for HPOUTR
channel, 0 for HPOUTL channel). This will adjust the DC offset correction on the selected channel by
no more than 1LSB (0.25mV).
Setting DCS_TIMER_PERIOD_01 or DCS_TIMER_PERIOD_23 to a non-zero value will cause a
single DC offset measurement and adjustment to be scheduled on a periodic basis. Periodic rates
ranging from every 0.52s to in excess of 2 hours can be selected.
Writing a logic 1 to DCS_TRIG_SERIES_n initiates a series of DC offset measurements and applies
the necessary correction to the associated output. The number of DC Servo operations performed is
determined by DCS_SERIES_NO_01 or DCS_SERIES_NO_23. A maximum of 128 operations may
be selected, though a much lower value will be sufficient in most applications.
The DC Servo control fields associated with active modes (suitable for use on a signal path that is in
active use) are described in Table 53.
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PP, Rev 3.3, September 2012
88