WM8903 datasheet(78/178 Pages) WOLFSON

78 / 178 page

WM8903

Production Data

PD, Rev 4.5, June 2012

A pop-suppressed start-up requires VMID to be enabled smoothly, without the step change normally

associated with the initial stage of the VMID capacitor charging. A pop-suppressed start-up also

requires the analogue bias current to be enabled throughout the signal path prior to the VMID

reference voltage being applied. The WM8903 incorporates pop-suppression circuits which address

these requirements.

The alternate current source (Start-Up Bias) is enabled by STARTUP_BIAS_ENA. The start-up bias

is selected (in place of the normal bias) by POBCTRL. It is recommended that the start-up bias is

used during start-up, before switching back to the higher quality, normal bias.

VMID_IO_ENA has the same functionality as STARTUP_BIAS_ENA. The start-up bias is enabled by

setting either of these bits.

A soft-start circuit is provided in order to control the switch-on of the VMID reference. The soft-start

control circuit is enabled by setting VMID_SOFT. Three slew rates are provided, under control of the

VMID_SOFT field. When the soft-start circuit is enabled prior to enabling VMID_RES, the reference

voltage rises smoothly, without the step change that would otherwise occur. It is recommended that

the soft-start circuit and the output signal path be enabled before VMID is enabled by VMID_RES.

A soft shut-down is provided, using the soft-start control circuit and the start-up bias current

generator. The soft shut-down of VMID is achieved by setting VMID_SOFT, STARTUP_BIAS_ENA

and POBCTRL to select the start-up bias current and soft-start circuit prior to setting VMID_RES=00.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R4 (04h)

Bias Control

POBCTRL

Selects the bias current source

0 = Normal bias

1 = Start-Up bias

STARTUP_BIAS_

ENA

Enables the Start-Up bias current

generator

0 = Disabled

1 = Enabled

R5 (05h)

VMID

Control 0

VMID_IO_ENA

Enables the Start-Up bias current

generator

0 = Disabled

1 = Enabled

(same functionality as

STARTUP_BIAS_ENA)

4:3

VMID_SOFT [1:0]

VMID soft start enable / slew rate

control

00 = Disabled

01 = Fast soft start

10 = Nominal soft start

11 = Slow soft start

Table 50 Soft Start Control

WM8903 Datasheet(PDF) 78 Page - Wolfson Microelectronics plc

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