Production Data
WM8955BL
ANALOGUE OUTPUTS
ENABLING THE OUTPUTS
Each analogue output of the WM8955BL 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 the WM8955BL is in OFF mode, as this may cause
pop noise (see Minimising Pop Noise at the Analogue Outputs)
REGISTER
ADDRESS
BIT
LABEL
LOUT1
DEFAULT
DESCRIPTION
R26 (1Ah)
6
0
0
0
0
0
0
0 = LOUT1 disabled
Power
Management
(2)
1 = LOUT1 enabled
0 = ROUT1 disabled
1 = ROUT1 enabled
0 = LOUT2 disabled
1 = LOUT2 enabled
0 = ROUT2 disabled
1 = ROUT2 enabled
0 = MONOOUT disabled
1 = MONOOUT enabled
0 = OUT3 disabled
1 = OUT3 enabled
5
4
3
2
1
ROUT1
LOUT2
ROUT2
MONO
OUT3
Table 11 Analogue Output Control
Whenever an analogue output is disabled, it remains connected to VREF 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.
REGISTER
ADDRESS
BIT
LABEL
VROI
DEFAULT
DESCRIPTION
R27 (1Bh)
6
0
VREF to analogue output resistance
Additional (3)
0: 1.5 kΩ
1: 40 kΩ
Table 12 Disabled Outputs to VREF Resistance
THERMAL SHUTDOWN
The earpiece and headphone outputs can drive very large currents. To protect the WM8955BL from
overheating, a thermal shutdown circuit is included. If the device temperature reaches approximately
1500C and the thermal shutdown circuit is enabled (TSDEN = 1) then the output amplifiers (outputs
OUT1L/R, OUT2L/R & OUT3) will be disabled.
REGISTER
ADDRESS
BIT
LABEL
TSDEN
DEFAULT
DESCRIPTION
R23 (17h)
8
0
Thermal Shutdown Enable
0 : thermal shutdown disabled
1 : thermal shutdown enabled
Additional (1)
Table 13 Thermal Shutdown
PD Rev 4.1 February 2007
23
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
