wm8988 Wolfson Microelectronics plc, wm8988 Datasheet - Page 33

• Manufacturer Part Number: wm8988
• Description: Stereo Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

Production Data
w
ENABLING THE OUTPUTS
THERMAL SHUTDOWN
Each analogue output of the WM8988 can be separately enabled or disabled. The analogue mixer
associated with each output is powered on or off along with the output pin. All outputs are disabled by
default. To save power, unused outputs should remain disabled.
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)
Table 28 Analogue Output Control
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
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 29 Disabled Outputs to VREF Resistance
The headphone outputs can drive very large currents. To protect the WM8988 from overheating a
thermal shutdown circuit is included. If the device temperature reaches approximately 150
thermal shutdown circuit is enabled (TSDEN = 1 ) then the headphone amplifiers (outputs OUT1L/R
and OUT2L/R) will be disabled.
Table 30 Thermal Shutdown
R26 (1Ah)
Power
Management
(2)
Note: All “Enable” bits are 1 = Enabled, 0 = Disabled
R27 (1Bh)
Additional (1)
R23 (17h)
Additional
Control (1)
REGISTER
REGISTER
REGISTER
ADDRESS
ADDRESS
ADDRESS
6
5
4
3
6
8
BIT
BIT
BIT
LOUT1
ROUT1
LOUT2
ROUT2
VROI
TSDEN
LABEL
LABEL
LABEL
0
0
0
0
0
0
DEFAULT
DEFAULT
DEFAULT
LOUT1 Enable
ROUT1 Enable
LOUT2 Enable
ROUT2 Enable
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, October 2008
WM8988
0
C and the
33