WM8988 datasheet(33/56 Pages) WOLFSON

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Production Data

WM8988

PD, Rev 4.0, October 2008

ENABLING THE OUTPUTS

Each analogue output of the WM8988 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

R26 (1Ah)

Power

Management

(2)

ROUT2

ROUT2 Enable

Note: All “Enable” bits are 1 = Enabled, 0 = Disabled

Table 28 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 29 Disabled Outputs to VREF Resistance

THERMAL SHUTDOWN

The headphone outputs can drive very large currents. To protect the WM8988 from overheating a

thermal shutdown circuit is included. If the device temperature reaches approximately 150

0C and the

thermal shutdown circuit is enabled (TSDEN = 1 ) then the headphone amplifiers (outputs OUT1L/R

and OUT2L/R) will be disabled.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R23 (17h)

Additional

Control (1)

TSDEN

Thermal Shutdown Enable

0 : thermal shutdown disabled

1 : thermal shutdown enabled

Table 30 Thermal Shutdown

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