WM8731SEDSSLASHR datasheet(29/63 Pages) WOLFSON

29 / 63 page

WM8731 / WM8731L

Production Data

PD Rev 4.3 August 2006

The recommended external components are shown in Figure 20.

AGND

LINEOUT

Figure 20 Line Outputs Application Drawing

Recommended values are C1 = 10

µF, R1 = 47k, R2 = 100 Ω.

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 WM8731/L has a stereo headphone output available on LHPOUT and RHPOUT. The output is

designed specifically for driving 16 or 32

Ω headphones with maximum efficiency and low power

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

function.

The scheme of the circuit is shown in Figure 21.

VMID

HPOUT

FROM

DAC VIA

LINEOUT

Figure 21 Headphone Amplifier Schematic

LHPOUT and RHPOUT volumes can be independently adjusted under software control using the

LHPVOL[6:0] and RHPVOL[6:0] bits respectively of the headphone output control registers. The

adjustment is logarithmic with an 80dB range in 1dB steps from +6dB to –73dB.

The headphone outputs can be separately muted by writing codes less than 0110000 to

LHPVOL[6:0] or RHPVO[6:0]L bits. Whenever the headphone outputs are 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.

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