Production Data
WM8737L
The signal inputs are internally high-impedance biased to the reference voltage, VREF. Whenever
line inputs are muted or the device is placed into standby mode 2 (see “Power Management” section),
the inputs stay biased to VREF. This reduces any audible clicks that may otherwise be heard when
changing inputs or awakening from standby.
DC MEASUREMENT
For dc measurements (battery voltage monitoring for example), the LINPUT1 and/or RINPUT1 pins
can be taken directly into the respective ADC, bypassing the microphone preamplifier and PGA.
In dc mode the ADC output is mid-scale for L/RINPUT1 voltage AGND and full-scale for L/RINPUT
voltage 1.7 x AVDD. Note that L/RINPUT1 must not exceed AVDD and so a voltage divider will be
required to bring the battery voltage into range.
REGISTER
ADDRESS
BIT
LABEL
LINSEL
DEFAULT
DESCRIPTION
R2 (02h)
00
Left Channel Input Select
00: LINPUT1
8:7
Analogue Audio
Path Control
01: LINPUT2
(Left Channel)
10: LINPUT3
11: dc measure on LINPUT1
Left Channel Microphone Gain Boost
00: 13dB boost
LMICBOOST[1:0]
00
6:5
01: 18dB boost
10: 28dB boost
11: 33dB boost
LMBE
0
Left Channel Mic Boost Enable
4
0: Mic preamp disabled, bypass switch
is closed.
1: Mic preamp is enabled, bypass
switch is open.
R3 (03h)
RINSEL
00
Right Channel Input Select
00: RINPUT1
8:7
Analogue Audio
Path Control
01: RINPUT2
(Right Channel)
10: RINPUT3
11: dc measure on RINPUT1
Right Channel Microphone Gain Boost
Same as LMICBOOST
Right Channel Mic Boost Enable
Same as LMBE
RMICBOOST[1:0]
RMBE
00
0
6:5
4
Table 2 Input Software Control
The internal VREF input bias may cause unwanted loading of any potential divider connected to
L/RINPUT1 for the purpose of dc measurement. In this case, the internal bias sources can be
disabled by setting the appropriate bits of register R10 to zero.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R10 (0Ah)
RINPUT1 dc BIAS
ENABLE
1
0: Disable dc bias to RINPUT1
1: Enable dc bias to RINPUT1
0: Disable dc bias to LINPUT1
1: Enable dc bias to LINPUT1
0
DC Measure
Control
LINPUT1 dc BIAS
ENABLE
1
1
Table 3 DC Measurement Bias Control
PD, Rev 4.4, January 2012
15
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
