WM8994ECSSLASHR datasheet(231/363 Pages) CIRRUS

231 / 363 page

WM8994

Rev 4.6

231

POP SUPPRESSION CONTROL

The WM8994

incorporates a number of features, including SilentSwitch™ technology, designed to

suppress pops normally associated with Start-Up, Shut-Down or signal path control. 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 WM8994, 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

“Analogue Output Signal Path” section.

Additional bias controls, also pre-programmed into Control Write Sequencer, are described in the

“Reference Voltages and Master Bias” section.

DISABLED LINE OUTPUT CONTROL

The line outputs are biased to VMID in normal operation. To avoid audible pops caused by a disabled

signal path dropping to AGND, the WM8994 can maintain these connections at VMID when the

relevant output stage is disabled. This is achieved by connecting a buffered VMID reference to the

output.

The buffered VMID reference is enabled by setting VMID_BUF_ENA. The output resistance is

selectable, using the VROI register bit.

Note that, if LINEOUTn_DISCH=1 (see Table 133), then the respective output will be discharged to

AGND, and will not be connected to VMID.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R55 (0037h)

Additional

Control

VROI

Buffered VMID to Analogue Line Output

Resistance (Disabled Outputs)

0 = 20k

 from buffered VMID to output

1 = 500

 from buffered VMID to output

R57 (0039h)

AntiPOP (2)

VMID_BUF

_ENA

VMID Buffer Enable

0 = Disabled

1 = Enabled (provided VMID_SEL > 00)

Table 132 Disabled Line Output Control

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