WM8946 datasheet(68/173 Pages) CIRRUS

68 / 173 page

WM8946

Rev 4.5

POP SUPPRESSION CONTROL

The WM8946 incorporates a number of features which are designed to suppress pops normally

associated with Start-Up, Shut-Down or signal path control. These include the option to maintain an

analogue output to VMID even when the output driver is disabled. In addition, there is the ability to

actively discharge an output to GND.

Note that, to achieve maximum benefit from these features, careful attention may be required to the

sequence and timing of these controls.

DISABLED OUTPUT CONTROL

The line outputs and speaker outputs are biased to VMID in normal operation. In order to avoid

audible pops caused by a disabled signal path dropping to GND, the WM8946 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. This is applied to any disabled

outputs, provided that the respective _VMID_OP_ENA bit is also set. The output resistance can be

either 1k

 or 20k, depending on the respective _VROI register bit.

The disabled output control bits are described in Table 46

. See “Output Signal Path” for details of how

to disable any of the audio outputs.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R2 (02h)

Power

management

VMID_BUF_ENA

VMID Buffer Enable.

(The buffered VMID may be applied

to disabled input and output pins.)

0 = Disabled

1 = Enabled

R42 (2Ah)

Output ctrl

SPKR_VMID_OP

_ENA

Buffered VMID to SPKOUTR

Enable

0 = Disabled

1 = Enabled

SPKL_VMID_OP_

ENA

Buffered VMID to SPKOUTL Enable

0 = Disabled

1 = Enabled

LINER_VMID_OP

_ENA

Buffered VMID to LINEOUTR

Enable

0 = Disabled

1 = Enabled

LINEL_VMID_OP

_ENA

Buffered VMID to LINEOUTL

Enable

0 = Disabled

1 = Enabled

SPK_VROI

Buffered VREF to SPKOUTL /

SPKOUTR resistance (Disabled

outputs)

0 = approx 20k

1 = approx 1k

LINE_VROI

Buffered VREF to LINEOUTL /

LINEOUTR resistance (Disabled

outputs)

0 = approx 20k

1 = approx 1k

Table 46 Disabled Output Control

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