WM8948ECSSLASHR datasheet(68/189 Pages) WOLFSON

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WM8948

Production Data

PD, May 2011, Rev 4.1

The VMID soft-start and fast start register controls are defined in Table 41.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R7 (07h)

Additional

control

VMID_FAST_

START

VMID (fast-start) Enable

0 = Disabled

1 = Enabled

STARTUP_BIAS_

ENA

Start-Up Bias Enable

0 = Disabled

1 = Enabled

BIAS_SRC

Bias Source select

0 = Normal bias

1 = Start-Up bias

6:5

VMID_RAMP [1:0]

VMID soft start enable / slew rate

control

00 = Disabled

01 = Fast soft start

10 = Normal soft start

11 = Slow soft start

Table 41 Soft Start Control

POP SUPPRESSION CONTROL

The WM8948 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 WM8948 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

Ω or 20kΩ, 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.

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