Output Switch; Thermal Shutdown; Speaker Output - Cirrus Logic WM8940 Manual

OUTPUT SWITCH

Rev 4.4
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.
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 41). 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 de-bounce circuit is clocked
21
from a slow clock with period 2
GPIOPOL CSB/GPIO
0 0
0 0
0 1
0 1
1 0
1 0
1 1
1 1
Table 41 Output Switch Operation (GPIOSEL=001)

THERMAL SHUTDOWN

The speaker outputs can drive very large currents. To protect the WM8940 from overheating a
thermal shutdown circuit is included. The thermal shutdown can be configured to produce an interrupt
when the device reaches approximately 125
REGISTER BIT LABEL
ADDRESS
R49 1 TSDEN
Output control
Table 42 Thermal Shutdown

SPEAKER OUTPUT

SPKOUTP/N can differentially drive a mono 8 Bridge Tied Load (BTL) speaker as shown below.
-1
WM8940
SPEAKER
SPKVOL
MIXER
Figure 22 Speaker Output Connection
x MCLK, enabled using the SLOWCLKEN register bit.
SPKNEN/ MONOEN
SPKPEN
0 X
1 X
X 0
X 1
X 0
X 1
0 X
1 X
o
C. See General Purpose Input/Output section.
DEFAULT
1 Thermal Shutdown Enable
0 : thermal shutdown disabled
1 : thermal shutdown enabled
SPKOUTN
V
SPKBOOST
SPKR
SPKOUTP
WM8940
SPEAKER MONO
ENABLED OUTPUT
ENABLED
No No
Yes No
No No
No Yes
No No
No Yes
No No
Yes No
DESCRIPTION
= Mono – (-Mono) = 2xMono
As an
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