WM8731 datasheet(44/56 Pages) WOLFSON

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WM8731

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 February 2001

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.

LINEINPD: Simultaneously powers down both the Line Inputs. This can be done dynamically without

any audible effects either on the ADC or to the Line Outputs in Bypass mode. This is of use when the

device enters Playback, Pause or Stop modes or the Microphone input has been selected.

MICPD: Simultaneously powers down both the Microphone Input and Microphone Bias. If this is done

dynamically, audible pops through the ADC will result. This will only be audible if the Microphone

Input is selected to the ADC at the time. If the state of MICPD is changed then the controlling DSP or

microprocessor should switch to select the Line Inputs as input to the ADC (INSEL) before changing

MICPD. This is of use when the device enters Playback, Pause or Stop modes or the Microphone

Input is not selected.

ADCPD: Powers down the ADC and ADC Filters. If this is done dynamically then audible pops will

result if any signals were present through the ADC. To overcome this whenever the ADC is to be

powered down, either mute the Microphone Input (MUTEIN) or MUTELINEIN, then change ADCPD.

This is of use when the device enters Playback, Pause or Stop modes regardless of whether

Microphone or Line Inputs are selected.

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 Record,

Pause, Stop or Bypass 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.

OSCPD: Powers off the on board crystal oscillator. The MCLK input will function independently of the

Oscillator being powered down.

CLKOUTPD: Powers down the CLOCKOUT pin. This conserves power, reduces digital noise and RF

emissions if not required. CLKOUT is tied low when powered down.

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

under software control as shown in Table 18. If the crystal oscillator and/or CLOKOUT pins are being

used to derive the system master clock, these should probably never be powered off in standby.

Provision has been made to independently power off these areas according to Table 26.

DESCRIPTION

0001111

STANDBY, but with Crystal

Oscillator OS and CLKOUT

available

0101111

STANDBY, but with Crystal

Oscillator OS available,

CLKOUT not-available

0111111

STANDBY, Crystal

oscillator and CLKOUT not-

available.

Table 26 Standby Mode

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 inputs, 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

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