WM8903 datasheet(79/178 Pages) WOLFSON

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Production Data

WM8903

PD, Rev 4.5, June 2012

POP SUPPRESSION CONTROL

The WM8903 incorporates Wolfson’s SilentSwitch™ technology which enables pops normally

associated with Start-Up, Shut-Down or signal path control to be suppressed. To achieve maximum

benefit from these features, careful attention is required to the sequence and timing of these controls.

Note that, under the recommended usage conditions of the WM8903, these features will be

configured by running the default Start-Up and Shut-Down sequences as described in the “Control

Write Sequencer” section. In these cases, the user does not need to set these register fields directly.

The Pop Suppression controls relating to the Headphone / Line Output drivers are described in the

“Output Signal Path” section.

DISABLED INPUT / OUTPUT CONTROL

The analogue inputs to the WM8903 and the Differential Line (Speaker) outputs are biased to VMID

in normal operation. In order to avoid audible pops caused by a disabled signal path dropping to

AGND, the WM8903 can maintain these connections at VMID when the relevant input or output stage

is disabled. This is achieved by connecting a buffered VMID reference to the input or output. The

buffered VMID reference is enabled by setting VMID_BUF_ENA.

When the buffered VMID reference is enabled, it is connected to any unused input pins by setting the

BUFIO_ENA register bit. When buffered VMID is enabled, it is connected to any disabled Differential

Line outputs (speaker driver outputs) by setting VMID_TIE_ENA. The resistance associated with

VMID_TIE_ENA can be either 500

 or 20k, depending on the VROI register bit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R5 (05h)

VMID

Control 0

VMID_TIE_ENA

VMID buffer to Differential Lineouts

0 = Disabled

1 = Enabled

(only applies when relevant outputs

are disabled, ie. SPLK=0 or SPKR=0.

Resistance is controlled by VROI.)

BUFIO_ENA

VMID buffer to unused Inputs/Outputs

0 = Disabled

1 = Enabled

VMID_BUF_ENA

VMID Buffer Enable

0 = Disabled

1 = Enabled

R65 (41h)

VROI

Select VMID_TIE_ENA resistance for

disabled Differential Lineouts

0 = 20k ohm

1 = 500 ohm

Table 51 Disabled Input / Output Control

DIFFERENTIAL LINE OUTPUT DISCHARGE CONTROL

The differential line output paths can be actively discharged to AGND through internal resistors if

desired. This is desirable at start-up in order to achieve a known output stage condition prior to

enabling the soft-start VMID reference voltage. This is also desirable in shut-down to prevent the

external connections from being affected by the internal circuits. The Differential Line outputs

(speaker driver outputs) can be discharged to AGND by setting SPK_DISCHARGE.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R65 (41h)

SPK_DISCHARG

Speaker Discharge Enable

0 = Disabled

1 = Enable

Table 52 Differential Line Output Discharge Control

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