wm8987 Wolfson Microelectronics plc, wm8987 Datasheet - Page 35

• Manufacturer Part Number: wm8987
• Description: Stereo Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

Production Data
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ENABLING THE OUTPUTS
The analogue outputs and output mixers of the WM8987L can be separately enabled or disabled as
shown in Table 29.
Table 29 Analogue Output Control
All outputs and mixers are disabled by default. To save power, they should remain disabled
whenever possible. Outputs can be enabled at any time, except when VREF is disabled (VR=0), as
this may cause pop noise (see “Power Management” and “Applications Information” sections).
Whenever an analogue output is disabled, it remains connected to the VREF voltage through an
internal resistor. This helps to prevent pop noise when the output is re-enabled. The resistance
between VREF and each output can be controlled using the VROI bit in register 27. The default is
low (1.5kΩ), 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 40kΩ.
Table 30 Disabled Outputs to VREF Resistance
THERMAL SHUTDOWN
The analogue outputs can drive large currents. To protect the WM8987L from overheating, a thermal
shutdown circuit is included. If the device temperature reaches approximately 150
shutdown circuit is enabled (TSDEN = 1) then the output amplifiers (pins ROUT1, LOUT2, ROUT2
and OUT3) are disabled.
Table 31 Thermal Shutdown
R26 (1Ah)
Power
Management
(2)
Note: All “Enable” bits are 1 = ON, 0 = OFF
R27 (1Bh)
Additional (1)
R23 (17h)
Additional
Control (1)
REGISTER
REGISTER
REGISTER
ADDRESS
ADDRESS
ADDRESS
5
4
3
2
1
6
8
BIT
BIT
BIT
ROUT1
LOUT2
ROUT2
MONO
OUT3
VROI
TSDEN
LABEL
LABEL
LABEL
0
0
0
0
0
0
0
DEFAULT
DEFAULT
DEFAULT
Enables ROUT1 and right mixer
Enables LOUT2 and left mixer
Enables ROUT2 and right mixer
Enable mono mixer
Enables OUT3
VREF to analogue output resistance
0: 1.5 kΩ
1: 40 kΩ
Thermal Shutdown Enable
0 : thermal shutdown disabled
1 : thermal shutdown enabled
DESCRIPTION
DESCRIPTION
DESCRIPTION
PD Rev 4.0 August 2008
0
C and the thermal
WM8987L
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