WM8711

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WOLFSON MICROELECTRONICS LTD

PP Rev 1.2 November 2000

12

VMID

FROM LINE

INPUTS

LINEOUT

FROM DAC

BYPASS

TO HEADPHONE AMP

DACSEL

Figure 8 Line Output Schematic

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

the BYPASS path. 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 3.

REGISTER

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

3

BYPASS

1

Bypass Switch

1 = Enable Bypass

0 = Disable Bypass

0000100

Analogue

Audio Path

Control

4

DACSEL

0

DAC Select

1 = Select DAC

0 = Don’t select DAC

Table 3 Output Software Control

The recommended external components are shown in Figure 9.

AGND

R1

C1

AGND

LINEOUT

R2

Figure 9 Line Outputs Application Drawing

Recommended values are C1 = 470nF (10V npo type), R1 = 47KOhms, R2 = 100 Ohms

C1 forms a DC blocking capacitor to the line outputs. R1 prevents the output voltage from drifting so

protecting equipment connected to the line output. R2 forms a de-coupling resistor preventing

abnormal loads from disturbing the device. Note that poor choice of dielectric material for C1 can

have dramatic effects on the measured signal distortion at the output.