WM8753 Wolfson Microelectronics plc, WM8753 Datasheet - Page 46

• Manufacturer Part Number: WM8753
• Description: HI FI AND TELEPHONY DUAL CODEC
• Manufacturer: Wolfson Microelectronics plc

Advanced Information
HEADPHONE SWITCH
w
Table 43 Disabled Outputs to VREF Resistance
Table 44 Headphone Switch Operation
Table 45 Headphone Switch
Whenever an analogue output is disabled, it remains connected to VREF (pin 20) through a resistor.
This helps to prevent pop noise when the output is re-enabled. The resistance between VREF and
L/ROUT1, L/ROUT2 and MONO1 can be controlled using the VROI bit in register 27. The default is
low (500 ), 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 90k .
Pin 43 (GPIO4) 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, pin 43 switches between headphone and speaker outputs (e.g.
when pin 43 is connected to a mechanical switch in the headphone socket to detect plug-in). The
HPSWPOL bit reverses the polarity of pin 43. Note that the LOUT1, ROUT1, LOUT2 and ROUT2 bits
in register 22 must also be set for headphone and speaker output (see Table 44 and Table 45). The
GPIO4 pin has an internal pull-up/pull-down which can be enabled by setting register bits
GPIO4M[1:0]. For cap-less headphone connections a pull-down should be used if VMID is greater
than GPIO4 V
interrupt. See GPIO and Interrupt Controller Section. The GPIO4 input has a debounce circuit to
remove glitches on the input caused by a jack insert in order to prevent the outputs being powered on
and off. This debounce circuit is clocked from a slow clock with period = 2
clock can be selected to be either mclk or pcmclk using SLWCLK.
R45 (2Dh)
Additional (1)
R45 (2Dh)
Output
Control
R52 (34h)
Clock Control
HPSWEN
REGISTER
REGISTER
ADDRESS
ADDRESS
0
0
0
0
1
1
1
1
1
1
1
1
IH
HPSWPOL
, otherwise a pull-up should be used. GPIO4 can also be used to generate an
3
6
5
0
BIT
X
X
X
X
BIT
0
0
0
0
1
1
1
1
VROI
HPSWEN
HPSWPOL
SLWCLK
LABEL
LABEL
(pin 43)
GPIO4
X
X
X
X
0
0
1
1
1
1
0
0
0
0
0
0
L/ROUT1
(reg. 22)
DEFAULT
DEFAULT
X
X
X
X
0
0
1
1
0
1
0
1
L/ROUT2
(reg. 22)
VREF to analogue output resistance
0: 500
1: 90 k
Headphone Switch Enable
0 : Headphone switch disabled
1 : Headphone switch enabled
Headphone Switch Polarity
0 : GPIO4 high = headphone
1 : GPIO4 high = speaker
Timeout and Headphone switch clock
source
0 = mclk
1 = pcm clk
X
X
X
X
0
1
0
1
0
1
0
1
Headphone
enabled
DESCRIPTION
DESCRIPTION
yes
yes
yes
yes
no
no
no
no
no
no
no
no
21
x input clock. The input
AI Rev 3.1 June 2004
WM8753L
Speaker
enabled
yes
yes
yes
yes
no
no
no
no
no
no
no
no
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