wm8400 Wolfson Microelectronics plc, wm8400 Datasheet - Page 94

• Manufacturer Part Number: wm8400
• Description: Wolfson Audioplustm Hi-fi Audio Codec And Power Management Unit For Mobile Multimedia
• Manufacturer: Wolfson Microelectronics plc

WM8400
w
Figure 35 AC-Coupled Headphone Drive
Figure 37 Headphone and Ear Speaker Drive
When driving a handset ear speaker using OUT3 and OUT4 other than from RXP/RXN, the required
phase difference can be provided by inverting one of the DAC outputs or alternatively by mixing Left
and Right channels together using either LOMIX or ROMIX and muting the opposite channel.
Note that a differential output will provide an additional 6dB gain at the output pins. Register bits
OUT3ATTN and OUT4ATTN can be used to compensate for this gain if required.
Fully differential headphone drive is possible between LOUT and OUT3 and between ROUT and
OUT4. Routing LOPGA to OUT3 and ROPGA to OUT4 results in a phase inversion at LOUT with
respect to OUT3 and at ROUT with respect to OUT4. This allows fully differential headset drive, with
greatly improved crosstalk performance, improved bass response, increased noise immunity and
removing the need for large and expensive DC-blocking capacitors.
To ensure fully balanced differential operation, LOUT and OUT3 must be set to the same gain as
each other, and ROUT and OUT4 must be set to the same gain as each other. This is best achieved
by setting OUT3ATTN and OUT4ATTN to 0dB, whilst setting volume controls LOPGAVOL and
LOUTVOL at matching levels and setting volume controls ROPGAVOL and ROUTVOL at matching
levels.
Some example headphone output configurations are shown below.
Figure 36 Capless Mode Headphone Drive
Figure 38 Fully Differential Headphone Drive
PP, April 2009, Rev 3.0
Pre-Production
94