WM8904ECSSLASHR datasheet(66/188 Pages) WOLFSON

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WM8904

Pre-Production

PP, Rev 3.3, September 2012

DIGITAL-TO-ANALOGUE CONVERTER (DAC)

The WM8904 DACs receive digital input data from the DACDAT pin and via the digital sidetone path

(see “Digital Mixing” section). 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 Wolfson SmartDAC™

architecture offers reduced power consumption, whilst also delivering a reduction in 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 are sent directly to the output PGAs (see “Output Signal Path”).

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

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R18 (12h)

Power

Management

DACL_ENA

Left DAC Enable

0 = DAC disabled

1 = DAC enabled

DACR_ENA

Right DAC Enable

0 = DAC disabled

1 = DAC enabled

Table 32 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 is detailed in Table 34.

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 is loaded into the respective control register, but does 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

R30 (1Eh)

DAC Digital

Volume Left

DAC_VU

N/A

DAC Volume Update

Writing a 1 to this bit causes left

and right DAC volume to be

updated simultaneously

7:0

DACL_VOL [7:0]

1100_0000

(0dB)

Left DAC Digital Volume

00h = Mute

01h = -71.625dB

02h = -71.250dB

… (0.375dB steps)

C0h to FFh = 0dB

(See Table 34 for volume range)

R31 (1Fh)

DAC Digital

Volume Right

DAC_VU

N/A

DAC Volume Update

Writing a 1 to this bit causes left

and right DAC volume to be

updated simultaneously

7:0

DACR_VOL [7:0]

1100_0000

(0dB)

Right DAC Digital Volume

00h = Mute

01h = -71.625dB

02h = -71.250dB

… (0.375dB steps)

C0h to FFh = 0dB

(See Table 34 for volume range)

Table 33 DAC Digital Volume Control

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