WM8903 datasheet(82/178 Pages) WOLFSON

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WM8903

Production Data

PD, Rev 4.5, June 2012

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R67 (43h)

DC Servo 0

DCS_MASTER_ENA

DC Servo Master Control

0 = DC Servo Reset

1 = DC Servo Enabled

3:0

DCS_ENA [3:0]

0000

DC Servo Enable

[3] - HPOUTL enable

[2] - HPOUTR enable

[1] - LOUTL enable

[0] - LOUTR enable

R69 (45h)

DC Servo 2

1:0

DCS_MODE [1:0]

DC Servo Mode

00 = WRITE_STOP

01 = WRITE_UPDATE

10 = START_STOP

11 = START_UPDATE

Table 54 DC Servo Control

To reduce power consumption when unused audio outputs are disabled, the DC Servo correction

should also be disabled. The WM8903 provides the capability to quickly resume the necessary DC

Servo correction when the outputs are re-enabled, without the time delay associated with the

START_STOP mode of DC Servo operation.

If the DC Servo correction is disabled using the DCS_ENA bits, but the DCS_MASTER_ENA bit is

maintained at 1, then the DC Servo will retain the latest correction values in its memory. These values

will be re-applied when the DC Servo is later enabled via the DCS_ENA bits.

An alternative method to apply known correction settings is to read the correction values from the

WM8903 register map and to store these for later use. After DC offset correction has been performed,

the applicable correction values can be read from the fields in the Servo Readback registers R81 to

R84 described in Table 55.

Setting DCS_MODE to 00b or 01b selects WRITE_STOP mode and WRITE_UPDATE mode

respectively. WRITE_STOP mode is similar to START_STOP mode, except that the DC Servo

correction factors are read from internal registers, instead of being calculated from the measured

output conditions. In the same way, WRITE_UPDATE mode is similar to START_UPDATE mode.

When the DC Servo is commanded to one of these modes, the initial DC offset correction values are

read from the _WRITE_VAL field in registers R71 to R74 described in Table 55.

Selecting WRITE_STOP or WRITE_UPDATE mode applies initial settings which should be written to

registers R71 to R74 before the DC Servo is enabled. In WRITE_STOP mode, no further DC

correction is applied. In WRITE_UPDATE mode, the DC Servo will periodically measure and adjust

the DC offset correction. Similar to START_UPDATE mode, the default time between updates is

approximately 10 minutes.

WM8903 Datasheet(PDF) 82 Page - Wolfson Microelectronics plc

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