WM8978GEFLSLASHV datasheet(50/78 Pages) WOLFSON

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WM8978

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PP Rev 1.7 January 2005

ENABLING THE OUTPUTS

Each analogue output of the WM8978 can be separately enabled or disabled. The analogue mixer

associated with each output has a separate enable. All outputs are disabled by default. To save

power, unused parts of the WM8978 should remain disabled.

Outputs can be enabled at any time, but it is not recommended to do so when BUFIO is disabled

(BUFIOEN=0) or when BUFDCOP is disabled (BUFDCOPEN=0) when configured in output boost

mode, as this may cause pop noise (see “Power Management” and “Applications Information”

sections).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

BUFIOEN

Unused input/output tie off buffer enable

OUT3MIXEN

OUT3 mixer enable

OUT4MIXEN

OUT4 mixer enable

Power

Management

BUFDCOPEN

Output stage 1.5xAVDD/2 driver enable

ROUT1EN

ROUT1 output enable

LOUT1EN

LOUT1 output enable

Power

Management

SLEEP

0 = Normal device operation

1 = Residual current reduced in device

standby mode

LMIXEN

Left mixer enable

RMIXEN

Right mixer enable

ROUT2EN

ROUT2 output enable

LOUT2EN

LOUT2 output enable

OUT3EN

OUT3 enable

Power

Management

OUT4EN

OUT4 enable

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

Table 40 Output Stages Power Management Control

THERMAL SHUTDOWN

The speaker outputs can drive very large currents. To protect the WM8974 from overheating a

thermal shutdown circuit is included. If the device temperature reaches approximately 125

0C and the

thermal shutdown circuit is enabled (TSDEN=1) then the speaker amplifiers will be disabled if

TSDEN is set. The thermal shutdown may also be configured to generate an interrupt. See the GPIO

and Interrupt Controller section for details.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R49

Output Control

TSDEN

Thermal Shutdown Enable

0 : thermal shutdown disabled

1 : thermal shutdown enabled

Table 41 Thermal Shutdown

UNUSED ANALOGUE INPUTS/OUTPUTS

Whenever an analogue input/output is disabled, it remains connected to a voltage source (either

AVDD/2 or 1.5xAVDD/2 as appropriate) through a resistor. This helps to prevent pop noise when the

output is re-enabled. The resistance between the voltage buffer and the output pins can be

controlled using the VROI control bit. The default impedance is low, 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 30k

Ω.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R49

VROI

VREF (AVDD/2 or 1.5xAVDD/2) to

analogue output resistance

0: approx 1k

Ω

1: approx 30 k

Ω

Table 42 Disabled Outputs to VREF Resistance

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