Advanced Information

WM9708

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 April 2001

27

RECOMMENDED EXTERNAL COMPONENTS VALUES

COMPONENT

REFERENCE

SUGGESTED

VALUE

DESCRIPTION

C1 to C4

10nF

De-coupling for DVDD and AVDD

C5 to C17

470nF

AC coupling capacitors for setting DC level of analogue inputs to VCAP1.

Value chosen to give corner frequency below 20Hz for min 10K input impedance.

C18

1

µF

C19

0.1

µF

C20

10

µF

C21

0.1

µF

C22

10

µF

Reference de-coupling capacitors for ADC, DAC, Mixer and CAP2 references.

Ceramic type or similar.

C23

100nF

3D low pass filter. This value sets nominal 100Hz.

C24

47nF

3D high pass filter. This value sets nominal 1kHz.

C25 to C29

10

µF

Output AC coupling caps to remove VREF DC level from outputs.

C30 and C31

22pF

Optional capacitors for better crystal frequency stability.

XT

24.576 MHz

AC’97 master clock frequency. A bias resistor is not required, but if connected will not

affect operation if value is large (above 1M

Ω).

Table 16 External Component Values

RECOMMENDATIONS FOR 3.3V OPERATION

The device’s performance with AVDD = 3.3V is shown in Electrical Characteristics.

In 3.3V analogue operation, mid-rail reference scales to 1.5V. All ADC and DAC references are 3/5

ths

of their nominal 5V value. Input and output signals that are 1Vrms in 5V applications, scale to

660mVrms in 3.3V applications. If 1Vrms output is required, the mixer gain adjust PGAs need to be

increased by 3 times 1.5dB steps.