WM8955_06 Datasheet, PDF (25/46 Pages) Wolfson Microelectronics plc – Stereo DAC For Portable Audio Applications

Production Data
WM8955L
HEADPHONE SWITCH
The HPDETECT pin can be used as a headphone switch control input to automatically disable the
speaker output and enable the headphone output e.g. when a headphone is plugged into a jack
socket. In this mode, enabled by setting HPSWEN, HPDETECT switches between headphone and
speaker outputs (typically, the pin is connected to a mechanical switch in the headphone socket to
detect plug-in). The HPSWPOL bit reverses the pin’s polarity. HPDETECT has CMOS thresholds at
0.3 AVDD / 0.7 AVDD. Note that the LOUT1, ROUT1, LOUT2 and ROUT2 bits in register 26 must
also be set to enable headphone and speaker outputs (see tables below).
REGISTER
ADDRESS
R24 (18h)
Additional (1)
BIT
LABEL
6
HPSWEN
5
HPSWPOL
3
HPSWZC
Table 14 Headphone Switch
DEFAULT
DESCRIPTION
0
Headphone Switch Enable
0 : Headphone switch disabled
1 : Headphone switch enabled
0
Headphone Switch Polarity
0 : HPDETECT high = headphone
1 : HPDETECT high = speaker
0
Headphone Switch Zero Cross Enable
0 : Switch immediately
1 : Switch on zero crossing only
HPSWEN HPSWPOL HPDETECT L/ROUT1
(PIN23) (reg. 26)
0
X
X
0
0
X
X
0
0
X
X
1
0
X
X
1
1
0
0
X
1
0
0
X
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
X
1
1
1
X
Table 15 Headphone Switch Operation
L/ROUT2
(reg. 26)
0
1
0
1
0
1
X
X
X
X
0
1
Headphone
enabled
no
no
yes
yes
no
no
no
yes
no
yes
no
no
Speaker
enabled
no
yes
no
yes
no
yes
no
no
no
no
no
yes
Figure 10 Example Headset Detection Circuit Using Normally-Open Switch
AVDD
HPSWEN = 1
HPSWPOL = 0
ROUT1
-
L/ROUT1 = L/ROUT2 = 1
LOUT1
-
headphone /
33k
speaker
switching
HPDETECT
switch opens
on insertion
LR
Figure 11 Example Headset Detection Circuit Using Normally-Closed Switch
w
PD Rev 4.2 March 2006
25