Production Data
WM8955BL
MINIMISING POP NOISE AT THE ANALOGUE OUTPUTS
To minimise any pop or click noise when the system is powered up or down, the following procedures
are recommended.
POWER UP
•
•
•
Switch on power supplies. By default the WM8955BL is in OFF Mode (i.e. only the control
interface is powered up)
Enable the reference voltage VREF by setting the WM8955BL to Standby mode. DO NOT
enable any of the analogue outputs at this point.
Allow VREF to settle. The settling time depends on the value of the capacitor connected at
VMID, and the size of the resistors selected using VMIDSEL (τ = RC).
•
•
•
Enable DACs, etc. as required.
Enable outputs required.
Set DACMU = 0 to soft-un-mute the audio DACs.
POWER DOWN
•
•
•
Set DACMU = 1 to soft-mute the audio DACs.
Disable outputs.
Switch off the power supplies.
LINE OUTPUT CONFIGURATION
All the analogue outputs, LOUT1/ROUT1, LOUT2/ROUT2, and MONOOUT, can be used as line
outputs. Recommended external components are shown below.
C1
R1
1uF
100 Ohm
LINE-OUT SOCKET
(LEFT)
LOUT2
ROUT2
AGND
AGND
WM8955BL
LINE-OUT SOCKET
(RIGHT)
C2
1uF
R2
100 Ohm
Figure 29 Recommended Circuit for Line Output
The DC blocking capacitors and the load resistance together determine the lower cut-off frequency, fc.
Assuming a 10 kΩ load and C1, C2 = 1μF:
fc = 1 / 2π (RL+R1) C1 = 1 / (2π x 10.1kΩ x 1μF) = 16 Hz
Increasing the capacitance lowers fc, improving the bass response. Smaller values of C1 and C2 will
diminish the bass response. The function of R1 and R2 is to protect the line outputs from damage
when used improperly.
PD Rev 4.1 February 2007
41
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
