WM8721_04 Datasheet, PDF (13/37 Pages) Wolfson Microelectronics plc – Internet Audio DAC with Integrated Headphone Driver

Production Data
WM8721 / WM8721L
FROM DAC
DACSEL
VMID
LINEOUT
TO HEADPHONE AMP
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 BIT
ADDRESS
LABEL
0000100
4
DACSEL
Analogue
Audio Path
Control
Table 3 Output Software Control
DEFAULT
0
DESCRIPTION
DAC Select
1 = Select DAC
0 = Don’t select DAC
The recommended external components are shown in Figure 9.
LINEOUT
R2
C1
R1
AGND
AGND
Figure 9 Line Outputs Application Drawing
Recommended values are C1 = 10µF, 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.
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PD Rev 4.0 November 2004
13