WM8944BECSSLASHR datasheet(65/165 Pages) CIRRUS

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WM8944B

Rev 4.3

POP SUPPRESSION CONTROL

The WM8944B 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 WM8944B 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 42

. 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

SPKN_VMID_OP

_ENA

Buffered VMID to SPKOUTN

Enable

0 = Disabled

1 = Enabled

SPKP_VMID_OP

_ENA

Buffered VMID to SPKOUTP

Enable

0 = Disabled

1 = Enabled

LINE_VMID_OP_

ENA

Buffered VMID to LINEOUT Enable

0 = Disabled

1 = Enabled

SPK_VROI

Buffered VREF to SPKOUTP /

SPKOUTN resistance (Disabled

outputs)

0 = approx 20k ohms

1 = approx 1k4 ohms

LINE_VROI

Buffered VREF to LINEOUT

resistance (Disabled output)

0 = approx 20k ohms

1 = approx 1k1 ohms

Table 42 Disabled Output Control

OUTPUT DISCHARGE CONTROL

The line outputs and speaker outputs can be actively discharged to GND 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 individual control bits for discharging each audio output are described in Table 43.

WM8944BECS/R 数据表(PDF) 65 Page - Cirrus Logic

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