WM8955BLGECOSLASHRV datasheet(23/44 Pages) WOLFSON

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Production Data

WM8955BL

PD Rev 4.1 February 2007

ANALOGUE OUTPUTS

ENABLING THE OUTPUTS

Each analogue output of the WM8955BL 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 the WM8955BL is in OFF mode, as this may cause

pop noise (see Minimising Pop Noise at the Analogue Outputs)

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

LOUT1

0 = LOUT1 disabled

1 = LOUT1 enabled

ROUT1

0 = ROUT1 disabled

1 = ROUT1 enabled

LOUT2

0 = LOUT2 disabled

1 = LOUT2 enabled

ROUT2

0 = ROUT2 disabled

1 = ROUT2 enabled

MONO

0 = MONOOUT disabled

1 = MONOOUT enabled

R26 (1Ah)

Power

Management

(2)

OUT3

0 = OUT3 disabled

1 = OUT3 enabled

Table 11 Analogue Output Control

Whenever an analogue output is disabled, it remains connected to VREF through an internal 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 (3)

VROI

VREF to analogue output resistance

0: 1.5 k

1: 40 k

Table 12 Disabled Outputs to VREF Resistance

THERMAL SHUTDOWN

The earpiece and headphone outputs can drive very large currents. To protect the WM8955BL 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 output amplifiers (outputs

OUT1L/R, OUT2L/R & OUT3) will be disabled.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R23 (17h)

Additional (1)

TSDEN

Thermal Shutdown Enable

0 : thermal shutdown disabled

1 : thermal shutdown enabled

Table 13 Thermal Shutdown

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