WM8955BL Wolfson Microelectronics, WM8955BL Datasheet - Page 23

• Manufacturer Part Number: WM8955BL
• Description: Stereo DAC
• Manufacturer: Wolfson Microelectronics

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Production Data
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)
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.
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
150
OUT1L/R, OUT2L/R & OUT3) will be disabled.
Table 13 Thermal Shutdown
R26 (1Ah)
Power
Management
(2)
R27 (1Bh)
Additional (3)
R23 (17h)
Additional (1)
REGISTER
REGISTER
REGISTER
ADDRESS
ADDRESS
0
ADDRESS
C and the thermal shutdown circuit is enabled (TSDEN = 1) then the output amplifiers (outputs
6
5
4
3
2
1
6
8
BIT
BIT
BIT
LOUT1
ROUT1
LOUT2
ROUT2
MONO
OUT3
VROI
TSDEN
LABEL
LABEL
LABEL
0
0
0
0
0
0
0
0
DEFAULT
DEFAULT
DEFAULT
0 = LOUT1 disabled
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
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 4.1 February 2007
WM8955BL
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