WM8971L datasheet(35/61 Pages) WOLFSON

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Production Data

WM8971L

PD Rev 4.1 August 2005

ENABLING THE OUTPUTS

Each analogue output of the WM8971L can be separately enabled or disabled. The analogue mixer

associated with each output is powered on or off along with the output pin. All outputs are disabled by

default. To save power, unused outputs should remain disabled.

Outputs can be enabled at any time, except when VREF is disabled (VR=0), as this may cause pop

noise (see “Power Management” and “Applications Information” sections)

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

LOUT1

LOUT1 Enable

ROUT1

ROUT1 Enable

LOUT2

LOUT2 Enable

ROUT2

ROUT2 Enable

R26 (1Ah)

Power

Management

(2)

MONO

MONOOUT Enable

Note: All “Enable” bits are 1 = ON, 0 = OFF

Table 25 Analogue Output Control

Whenever an analogue output is disabled, it remains connected to VREF (pin 20) through a resistor.

This helps to prevent pop noise when the output is re-enabled. The resistance between VREF and

each output can be controlled using the VROI bit in register 27. The default is low (1.5k

Ω), so that

any capacitors on the outputs can charge up quickly at start-up. If a high impedance is desired for

disabled outputs, VROI can then be set to 1, increasing the resistance to about 40k

Ω.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R27 (1Bh)

Additional (1)

VROI

VREF to analogue output resistance

0: 1.5 k

Ω

1: 40 k

Ω

Table 26 Disabled Outputs to VREF Resistance

HEADPHONE SWITCH

The HPDETECT pin can be used as a headphone switch control input to automatically disable the

speaker output and enable the headphone output e.g. when a headphone is plugged into a jack

socket. In this mode, enabled by setting HPSWEN, HPDETECT switches between headphone and

speaker outputs (e.g. when the pin is connected to a mechanical switch in the headphone socket to

detect plug-in). The HPSWPOL bit reverses the pin’s polarity. Note that the LOUT1, ROUT1, LOUT2

and ROUT2 bits in register 26 must also be set for headphone and speaker output (see Table 27 and

Table 28).

HPSWEN

HPSWPOL HPDETECT

(PIN23)

L/ROUT1

(REG. 26)

L/ROUT2

(REG. 26)

HEADPHONE

ENABLED

SPEAKER

ENABLED

yes

Table 27 Headphone Switch Operation

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