WM8974GEFLSLASHV datasheet(47/87 Pages) WOLFSON

47 / 87 page

Production Data

WM8974

PD Rev 4.2 March 2007

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 45). 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 221 x MCLK, enabled using the SLOWCLKEN register bit.

GPIOPOL

CSB/GPIO

SPKNEN/

SPKPEN

MONOEN

SPEAKER

ENABLED

MONO

OUTPUT

ENABLED

Yes

Table 45 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. The thermal shutdown can be configured to produce an

interrupt when the device reaches approximately 125oC. See General Purpose Input/Output section.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R49

Output control

TSDEN

Thermal Shutdown Enable

0 : thermal shutdown disabled

1 : thermal shutdown enabled

Table 46 Thermal Shutdown

SPEAKER OUTPUT

SPKOUTP/N can differentially drive a mono 8

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

Figure 22 Speaker Output Connection

WM8974GEFL/V Datasheet(PDF) 47 Page - Wolfson Microelectronics plc

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