WM8988 datasheet(31/56 Pages) WOLFSON

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WM8988

PD, Rev 4.0, October 2008

ANALOGUE OUTPUTS

LOUT1/ROUT1 OUTPUTS

The LOUT1 and ROUT1 pins can drive a 16

Ω or 32Ω headphone or a line output (see Headphone

Output and Line Output sections, respectively). The signal volume on LOUT1 and ROUT1 can be

independently adjusted under software control by writing to LOUT1VOL and ROUT1VOL,

respectively. Note that gains over 0dB may cause clipping if the signal is large. Any gain setting

below 0101111 (minimum) mutes the output driver. The corresponding output pin remains at the

same DC level (the reference voltage on the VREF pin), so that no click noise is produced when

muting or un-muting.

A zero cross detect on the analogue output may also be enabled when changing the gain setting to

minimize audible clicks and zipper noise as the gain updates. If zero cross is enabled a timeout is

also available to update the gain if a zero cross does not occur. This function may be enabled by

setting TOEN in register R23 (17h).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

LO1VU

Left Volume Update

0 = Store LOUT1VOL in intermediate

latch (no gain change)

1 = Update left and right channel gains

(left = LOUT1VOL, right =

intermediate latch)

LO1ZC

Left zero cross enable

1 = Change gain on zero cross only

0 = Change gain immediately

R2 (02h)

LOUT1

Volume

6:0

LOUT1VOL

[6:0]

1111001

(0dB)

LOUT1 Volume

1111111 = +6dB

… (80 steps)

0110000 = -67dB

0111111 to 0000000 = Analogue

MUTE

RO1VU

Right Volume Update

0 = Store ROUT1VOL in intermediate

latch (no gain change)

1 = Update left and right channel gains

(left = intermediate latch, right =

ROUT1VOL)

RO1ZC

Right zero cross enable

1 = Change gain on zero cross only

0 = Change gain immediately

R3 (03h)

ROUT1

Volume

6:0

ROUT1VOL

[6:0]

1111001

ROUT1 Volume

1111111 = +6dB

… (80 steps)

0110000 = -67dB

0111111 to 0000000 = Analogue

MUTE

Table 24 LOUT1/ROUT1 Volume Control

LOUT1/ROUT1 COMMON GROUND FEEDBACK (HPCOM)

The LOUT1/ROUT1 outputs also have the option of incorporating common ground feedback from the

output signal ground, via a connection to the HPCOM input. This common ground feedback signal

should be AC-coupled via a 4.7uF capacitor for the headphone loads. AC coupling of these outputs if

they are used as LINE level outputs requires similar 1 to 4.7uF AC coupling capacitors depending

upon LINE load resistance.

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