WM8991 datasheet(137/174 Pages) WOLFSON

137 / 174 page

Pre-Production

WM8991

PP, May 2008, Rev 3.1

137

EXAMPLE CONTROL SEQUENCES

Pop-suppression control sequences are described below for typical WM8991 operations involving

start-up, muting and disabling of signal paths. Note that these descriptions are intended for guidance

only. Application software should be verified and tailored to ensure optimum performance.

Start-up sequence

The following sequence describes the register settings required to enable the headphone outputs

LOUT and ROUT. It assumes that VMID and VREF are initially disabled and actively discharged to

AGND.

STEP

DESCRIPTION

Discharge output drivers.

DIS_LOUT = 1

DIS_ROUT = 1

Time delay for output

capacitors to discharge.

Enable soft start control and

start-up bias source. Select

start-up bias.

SOFTST = 1

BUFCOPEN = 1

POBCTRL = 1

Disable active discharging of

VMID and Output drivers.

VMIDTOG = 0

DIS_LOUT = 0

DIS_ROUT = 0

Enable Output drivers.

LOUT_ENA = 1

ROUT_ENA = 1

Enable VMID and VREF.

VMID_MODE = 01

VREF_ENA = 1

Time delay for soft-start to

execute

Select default bias source.

POBCTRL = 0

Disable soft start control and

soft start voltage.

SOFTST = 0

BUFCOPEN = 0

Table 87 Example Start-Up Control Sequence

Output Mute sequence

The following sequence describes the register settings required to mute and disable the headphone

outputs LOUT and ROUT. It assumes that the soft start bias voltage is initially disabled.

STEP

DESCRIPTION

Enable buffered VMID at all

input and output circuits.

BUFIOEN = 1

Disable output drivers

LOUT_ENA = 0

ROUT_ENA = 0

Table 88 Example Mute Control Sequence

Output Un-Mute sequence

The following sequence describes the register settings required to enable and un-mute the

headphone outputs LOUT and ROUT.

STEP

DESCRIPTION

Enable Output drivers.

LOUT_ENA = 1

ROUT_ENA = 1

Disable buffered VMID at all

input and output circuits.

BUFIOEN = 0

Table 89 Example Un-Mute Control Sequence

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