WM8721

Product Preview

WOLFSON MICROELECTRONICS LTD

PP Rev 1.3 November 2000

12

VMID

LINEOUT

FROM DAC

TO HEADPHONE AMP

DACSEL

Figure 8 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 output is shown in Table 3.

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 = 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.

HEADPHONE AMPLIFIER

The WM8721 has a stereo headphone output available on LHPOUT and RHPOUT. The output is

designed specifically for driving 16 or 32 ohm headphones with maximum efficiency and low power

consumption. The headphone output includes a high quality volume level adjustment and mute

function.