WM8974 datasheet(38/63 Pages) WOLFSON

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WM8974

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PP Rev 1.1 September 2004

OUTPUT SWITCH

When the device is configured with a 2-wire interface the CSB/GPIO pin can be used as a switch

control input to automatically disable the speaker outputs and enable the mono output. For example

when a line is plugged into a jack socket. In this mode, enabled by setting GPIOSEL=001, pin

CSB/GPIO switches between mono and speaker outputs (e.g. when pin 12 is connected to a

mechanical switch in the headphone socket to detect plug-in). The GPIOPOL bit reverses the

polarity of the CSB/GPIO input pin.

Note that the speaker outputs and the mono output must be enabled for this function to work (see

Table 28).

The CSB/GPIO pin has an internal de-bounce circuit when in this mode in order to

prevent the output enables from toggling multiple times due to input glitches. This debounce circuit

is clocked from a slow clock with period 2

21 x MCLK, enabled using the SLOWCLKEN register bit.

GPIOPOL

CSB/GPIO

SPKNEN/

SPKPEN

MONOEN

SPEAKER

ENABLED

MONO

OUTPUT

ENABLED

Yes

Table 28 Output Switch Operation (GPIOSEL=001)

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 29 Thermal Shutdown

SPEAKER OUTPUT

SPKROUTP/N can differentially drive a mono 8

Ω Bridge Tied Load (BTL) speaker as shown below.

Figure 17 Speaker Output Connection

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