WM8734 datasheet(17/42 Pages) ETC

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WM8734

Advanced Information

AI Rev 2.2 November 2001

LINE OUTPUTS

The WM8734 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 14. 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

LINEOUT

FROM DAC

TO HEADPHONE AMP

DACSEL

Figure 14 Line Output Schematic

The line output is muted by either muting the DAC (analogue) or Soft Muting (digital). 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 4.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000100

Analogue

Audio Path

Control

DACSEL

DAC Select

1 = Select DAC

0 = Don’t select DAC

Table 4 Output Software Control

The recommended external components are shown in Figure 15.

AGND

LINEOUT

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