Production Data

WM8721 / WM8721L

w

PD Rev 4.0 November 2004

13

VMID

LINEOUT

FROM DAC

TO HEADPHONE AMP

DACSEL

Figure 8 Line Output Schematic

The line output is muted by either programming the DACMU (digital) bit as per table 2, or by writing

to the DACSEL (analogue) bit as per table 3. 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.

REGISTER

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

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 = 10

µF, R1 = 47k, R2 = 100Ω

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.