WM8746

Production Data

w

March 2006, PD Rev 4.0

30

It is important that the supply pins are connected correctly. If AVDD1 and AVDD2 pins had both been

connected to the 10Ω resistor, the performance would be worse. The value of 10Ω is too high and will

cause an increase in THD. This is because currents drawn by AVDD1 will affect the reference

voltage on AVDD2. A full-scale output FFT plot will show increased harmonics, because the output

current drawn modulates the reference voltage.

4.7µF ceramic capacitors are becoming available in 0805 package with Y5V dielectric. Whilst they do

not have quite as good performance as 10µF, it is possible to use them instead. Their capacitance

goes down significantly with supply voltage, but at 3.3V (VDD) and 1.65V (CAP pin), the drop is not

too great, if a 10V-rated part is used. As they are already in a low-inductance package, the 0.1µF is

no longer necessary. See Figure 26 for an example.

Figure 26 Decoupling Example 2

RECOMMENDED ANALOGUE LOW-PASS FILTER (OPTIONAL)

+

_

+

+VS

-VS

10u

F

51

Ω

7.5K

Ω

680pF

1.8k

Ω

10k

Ω

4.7k

Ω

4.7k

Ω

1.0nF

Figure 27 Recommended Low Pass Filter (Optional)