WM8955BLGECOSLASHV datasheet(41/44 Pages) WOLFSON

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Production Data

WM8955BL

PD Rev 4.1 February 2007

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.

AGND

LINE-OUT SOCKET

(LEFT)

1uF

100 Ohm

LOUT2

ROUT2

WM8955BL

100 Ohm

LINE-OUT SOCKET

(RIGHT)

1uF

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 k

Ω 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.

WM8955BLGECO/V 数据表(PDF) 41 Page - Wolfson Microelectronics plc

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