WM8904ECSSLASHR datasheet(88/188 Pages) WOLFSON

88 / 188 page

WM8904

Pre-Production

PP, Rev 3.3, September 2012

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

7:4

DCS_DAC_WR_C

OMPLETE [3:0]

0000

DC Servo DAC Write status

[3] - LINEOUTR

[2] - LINEOUTL

[1] - HPOUTR

[0] - HPOUTL

0 = DAC Write DC Servo mode not

completed.

1 = DAC Write DC Servo mode

complete.

3:0

DCS_STARTUP_

COMPLETE [3:0]

0000

DC Servo Start-Up status

[3] - LINEOUTR

[2] - LINEOUTL

[1] - HPOUTR

[0] - HPOUTL

0 = Start-Up DC Servo mode not

completed..

1 = Start-Up DC Servo mode

complete.

Table 52 DC Servo Enable and Start-Up Modes

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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