WM8731 Wolfson Microelectronics Ltd., WM8731 Datasheet - Page 27

• Manufacturer Part Number: WM8731
• Description: WM8731 : Low Power Audio Codec With Integrated Headphone Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8731
Figure 19 Line Outputs Application Drawing
Recommended values are C1 = 10 F, R1 = 47k, 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 WM8731 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.
The scheme of the circuit is shown in Figure 20.
Figure 20 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.
LINEOUT
DAC VIA
LINEOUT
FROM
VMID
C1
AGND
R1
R2
AI Rev 2.3 August 2001
Advanced Information
AGND
HPOUT
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