WM8955LEFL datasheet(41/43 Pages) WOLFSON

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WM8955L

Product Preview Rev 0.4 May2003

APPLICATIONS INFORMATION

MINIMISING POP NOISE AT THE ANALOGUE OUTPUTS

To minimise anypop or click noise when the system is powered up or down, the following procedures

are recommended.

POWER UP

•

Switch on power supplies. Bydefault the WM8955L is in OFF Mode (i.e. onlythe control

interface is powered up)

•

Enable the reference voltage VREF bysetting the WM8955L to Standbymode. DO NOT

enable anyof the analogue outputs at this point.

•

Allow VREF to settle. The settling time depends on the value of the capacitor connected at

VMID (formula TBD).

•

Enable outputs, DACs, etc. (sequence TBD)

•

Set ACTIVE = 1 to enable the Audio Interface

•

Set DACMU = 0 to soft-un-mute the audio DACs.

POWER DOWN

•

Set DACMU = 1 to soft-mute the audio DACs.

•

Disable functions (sequence TBD)

•

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.

AGND

LINE-OUT SOCKET

(LEFT)

1uF

100 Ohm

LOUT2

ROUT2

WM8955L

100 Ohm

LINE-OUT SOCKET

(RIGHT)

1uF

Figure 25 Recommended Circuit for Line Output

The DC blocking capacitors and the load resistance together determine the lower cut-off frequency,

fc. Assuming a 10 kOhm load and C1, C2 = 10

µF:

fc =1 /2

π (RL+R1)C1 =1 / (2π x 10.1kΩ x1µF) = 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.

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