WM8721

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WOLFSON MICROELECTRONICS LTD

PP Rev 1.3 November 2000

26

POWER DOWN MODES

The WM8721 contains power conservation modes in which various circuit blocks may be safely

powered down in order to conserve power. This is software programmable as shown in Table 18.

REGISTER

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

3

DACPD

0

DAC Power Down

1 = Enable Power Down

0 = Disable Power Down

4

OUTPD

0

Line Output Power Down

1 = Enable Power Down

0 = Disable Power Down

0000110

Power Down

Control

7

POWEROFF

0

Power Off Device

1 = Device Power Off

0 = Device Power On

Table 18 Power Conservation Modes Software Control

Note:

When writing to register 0000110 bits 0, 1, 2, 5 and 6 should be set to 1.

The power down control can be used to either a) permanently disable functions when not required in

certain applications or b) to dynamically power up and down functions depending on the operating

mode, e.g.: during playback or record. Please follow the special instructions below if dynamic

implementations are being used.

DACPD: Powers down the DAC and DAC Digital Filters. If this is done dynamically then audible pops

will result unless the following guidelines are followed. In order to prevent pops, the DAC should first

be soft-muted (DACMU), the output should then be de-selected from the line and headphone output

(DACSEL), then the DAC powered down (DACPD). This is of use when the device enters Pause or

Stop modes.

OUTPD: Powers down the Line Headphone Output. If this is done dynamically then audible pops

may result unless the DAC is first soft-muted (DACMU). This is of use when the device enters

Record, Pause or Stop modes.

The device can be put into a standby mode (STANDBY) by powering down all the audio circuitry

under software control by setting DACPD and OUTPD, but not setting POWEROFF.

In STANDBY mode the Control Interface, a small portion of the digital and areas of the analogue

circuitry remain active. The active analogue includes the analogue VMID reference so that the

analogue line outputs and headphone outputs remain biased to VMID. This reduces any audible

effects caused by DC glitches when entering or leaving STANDBY mode.

The device can be powered off by writing to the POWEROFF bit of the Power Down register. In

POWEROFF mode the Control Interface and a small portion of the digital remain active. The

analogue VMID reference is disabled.