WM8904ECSSLASHR datasheet(83/188 Pages) WOLFSON

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Pre-Production

WM8904

PP, Rev 3.3, September 2012

POP SUPPRESSION CONTROL

The WM8904 incorporates Wolfson’s SilentSwitch™ technology which enables pops normally

associated with Start-Up, Shutdown 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 WM8904, these features will be

configured by running the default Start-Up and Shutdown 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 CONTROL

The analogue inputs to the WM8904 are biased to VMID in normal operation. In order to avoid

audible pops caused by a disabled signal path dropping to AGND, the WM8904 can maintain these

connections at VMID when the relevant input stage is disabled. This is achieved by connecting a

buffered VMID reference to the input. 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.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R5 (05h)

VMID

Control 0

VMID_BUF_ENA

VMID buffer to unused Inputs/Outputs

0 = Disabled

1 = Enabled

VMID_ENA

VMID Buffer Enable

0 = Disabled

1 = Enabled

Table 50 Disabled Line Input Control

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