WM8731SEDSSLASHR datasheet(28/63 Pages) WOLFSON

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WM8731 / WM8731L

Production Data

PD Rev 4.3 August 2006

The DAC converts the multi-level digital audio data stream from the DAC digital filters into high

quality analogue audio.

LINE OUTPUTS

The WM8731/L provides two low impedance line outputs LLINEOUT and RLINEOUT, suitable for

driving typical line loads of impedance 10K and capacitance 50pF. The line output is used to

selectively sum the outputs from the DAC or/and the Line inputs in bypass mode.

The LLINEOUT and RLINEOUT outputs are only available at a line output level and are not level

adjustable in the analogue domain, having a fixed gain of 0dB. The level is fixed such that at the DAC

full scale level the output level is Vrms at AVDD = 3.3 volts. Note that the DAC full scale level tracks

directly with AVDD. The scheme is shown in Figure 19. The line output includes a low order audio

low pass filter for removing out-of band components from the sigma-delta DAC. Therefore no further

external filtering is required in most applications.

VMID

FROM LINE

INPUTS

LINEOUT

FROM DAC

BYPASS

TO HEADPHONE AMP

DACSEL

FROM MICROPHONE

INPUT

SIDETONE

Figure 19 Line Output Schematic

The DAC output, Line Input and microphone are summed into the Line Output. In DAC mode only the

output from the DAC is routed to the line outputs. In Bypass mode the Line Input is summed into the

Line Outputs. In Side Tone mode the Microphone Input is summed into the Line Output. These

features can be used for either over-dubbing or, if the DAC is muted, as a pure analogue bypass or

Side Tone feature, so avoiding any digital signal processing.

The line output is muted by either muting the DAC (analogue) or Soft Muting (digital) and disabling

the BYPASS and SIDETONE paths. Refer to the DAC section for more details. Whenever the DAC

is muted or the device placed into standby mode the DC voltage is maintained at the line outputs to

prevent any audible clicks from being present.

The software control for the line outputs is shown in Table 8.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

BYPASS

Bypass Switch

1 = Enable Bypass

0 = Disable Bypass

DACSEL

DAC Select

1 = Select DAC

0 = Don’t select DAC

0000100

Analogue

Audio Path

Control

SIDETONE

Side Tone Switch

1 = Enable SideTone

0 = Disable Side Tone

Table 8 Output Software Control

WM8731SEDS/R 数据表(PDF) 28 Page - Wolfson Microelectronics plc

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