wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 79

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wm8918

Manufacturer Part Number
wm8918
Description
Ultra Low Power Dac For Portable Audio Applications
Manufacturer
Wolfson Microelectronics plc
Datasheet

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Table 48 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 48. 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.
R77 (4Dh)
DC Servo
Readback 0
REGISTER
ADDRESS
11:8
BIT
7:4
3:0
DCS_CAL_COMP
DCS_STARTUP_
COMPLETE [3:0]
COMPLETE [3:0]
DCS_DAC_WR_
LETE [3:0]
LABEL
DEFAULT
0000
0000
0000
DC Servo Complete status
[3] - LINEOUTR
[2] - LINEOUTL
[1] - HPOUTR
[0] - HPOUTL
0 = DAC Write or Start-Up DC Servo
mode not completed.
1 = DAC Write or Start-Up DC Servo
mode complete.
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.
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.
PD, Rev 4.0, September 2010
DESCRIPTION
WM8918
79

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