WM8956CGEFLSLASHV datasheet(36/80 Pages) WOLFSON

36 / 80 page

WM8956

Production Data

PD, November 2011, Rev 4.1

CLASS D SPEAKER OUTPUTS

The class D speaker outputs SPK_LN/SPK_LP and SPK_RN/SPK_RP can drive 1W into 8

 BTL

speakers. Class D outputs reduce power consumption and maximise efficiency by reducing power

dissipated in the output drivers, delivering most of the power directly to the load. This is achieved by

pulse width modulation (PWM) of a high frequency square wave, allowing the audio signal level to be

set by controlling the pulse width. The frequency of the output waveform is controlled by DCLKDIV,

and is derived from SYSCLK.

When the speakers are close to the device (typically less than about 100mm) the internal filtering

effects of the speaker can be used. Where signals are routed over longer distances, it is

recommended to use additional passive filtering, positioned close to the WM8956, to reduce EMI. See

"Applications Information" for more information on EMI reduction.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R8 (08h)

Clocking (2)

8:6

DCLKDIV

111

Controls clock division from

SYSCLK to generate suitable class

D clock.

000 = Reserved

001 = SYSCLK / 2

010 = SYSCLK / 3

011 = SYSCLK / 4

100 = SYSCLK / 6

101 = SYSCLK / 8

110 = SYSCLK / 12

111 = SYSCLK / 16

R49 (31h)

Class D

Control (1)

7:6

SPK_OP_EN

[1:0]

Enable Class D Speaker Outputs

00 = Off

01 = Left speaker only

10 = Right speaker only

11 = Left and right speakers enabled

Table 22 Class D Control Registers

The class D outputs require a PWM switching clock, which is derived from SYSCLK. This clock

should not be altered or disabled while the class D outputs are enabled.

See "Clocking and Sample Rates" for more information.

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