WM8991 datasheet(61/174 Pages) WOLFSON

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Pre-Production

WM8991

PP, May 2008, Rev 3.1

DIGITAL TO ANALOGUE CONVERTER (DAC)

The WM8991 DACs receive digital input data from the DACDAT pin and via the digital sidetone path.

The digital audio data is converted to oversampled bit streams in the on-chip, true 24-bit digital

interpolation filters. The bitstream data enters two multi-bit, sigma-delta DACs, which convert them to

high quality analogue audio signals. The multi-bit DAC architecture reduces high frequency noise and

sensitivity to clock jitter. It also uses a Dynamic Element Matching technique for high linearity and

low distortion.

The analogue outputs from the DACs can then be mixed with other analogue inputs using the output

mixers LOMIX, ROMIX and the speaker output mixer SPKMIX.

The DACs are enabled by the DACL_ENA and DACR_ENA register bits.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

DACL_ENA

(rw)

Left DAC Enable

0 = DAC disabled

1 = DAC enabled

R3 (03h)

DACR_ENA

(rw)

Right DAC Enable

0 = DAC disabled

1 = DAC enabled

Table 24 DAC Enable Control

DAC DIGITAL VOLUME CONTROL

The output level of each DAC can be controlled digitally over a range from -71.625dB to 0dB in

0.375dB steps. The level of attenuation for an eight-bit code X is given by:

0.375

× (X-192) dB for 1 ≤ X ≤ 192;

MUTE for X = 0

0dB for 192

≤ X ≤ 255

The DAC_VU bit controls the loading of digital volume control data. When DAC_VU is set to 0, the

DACL_VOL or DACR_VOL control data will be loaded into the respective control register, but will not

actually change the digital gain setting. Both left and right gain settings are updated when a 1 is

written to DAC_VU. This makes it possible to update the gain of both channels simultaneously.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

DAC_VU

N/A

DAC Volume Update

Writing a 1 to this bit will cause left

and right DAC volume to be updated

simultaneously

R11 (0Bh)

7:0

DACL_VOL

[7:0]

1100_0000b

(0dB)

Left DAC Digital Volume

(See Table 26 for volume range)

DAC_VU

N/A

DAC Volume Update

Writing a 1 to this bit will cause left

and right DAC volume to be updated

simultaneously

R12 (0Ch)

7:0

DACR_VOL

[7:0]

1100_0000b

(0dB)

Right DAC Digital Volume

(See Table 26 for volume range)

Table 25 DAC Digital Volume Control

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