wm9081 Wolfson Microelectronics plc, wm9081 Datasheet - Page 105

• Manufacturer Part Number: wm9081
• Description: Mono Dac With 2.6w Class Ab/d Speaker Driver, Dynamic Range Controller And Retune Mobile Parametric Equalizer
• Manufacturer: Wolfson Microelectronics plc

Pre-Production
APPLICATIONS INFORMATION
RECOMMENDED EXTERNAL COMPONENTS
Figure 67 Recommended external components
Notes
1.
2.
3.
4.
SPEAKER SELECTION
w
Wolfson recommend using a single, common ground reference. Where this is not possible, care should be taken to
optimise split ground configuration for audio performance.
Supply decoupling capacitors on DCVDD, DBVDD, SPKVDD and AVDD should be positioned as close to the
WM9081 as possible.
Capacitor types should be chosen carefully. Capacitors with very low ESR are recommended for optimum
performance.
The speakers should be connected as close as possible to the WM9081. When this is not possible, filtering should be
placed on the speaker outputs close the WM9081.
For filterless operation, it is important to select a speaker with appropriate internal inductance. The
internal inductance and the speaker's load resistance create a low-pass filter with a cut-off frequency
of:
e.g. for an 4Ω speaker and required cut-off frequency of 20kHz, the speaker should be chosen to
have an inductance of:
Care should be taken to ensure that the cut-off frequency of the speaker's internal filtering is low
enough to prevent speaker damage. The class D output of the WM9081 operate at much higher
frequencies than is recommended for most speakers, and the cut-off frequency of the filter should be
low enough to protect the speaker.
f
L = R
c
= R
L
L
/ (2πL)
/ (2πf
c
) = 4Ω / (2π * 20kHz) = 32μH
PP, Rev 3.0, April 2009
WM9081
105