wm8961 Wolfson Microelectronics plc, wm8961 Datasheet - Page 108

• Manufacturer Part Number: wm8961
• Description: Ultra-low Power Stereo Codec With 1w Stereo Class D Speaker Drivers And Ground Referenced Headphone Drivers
• Manufacturer: Wolfson Microelectronics plc

SPEAKER SELECTION
w
WM8961
For filter-less 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 8Ω speaker and required cut-off frequency of 20kHz, the speaker should be chosen to
have an inductance of:
8Ω speakers typically have an inductance in the range 20μH to 100μH. 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 outputs of the WM8961 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.
Figure 65 Speaker Equivalent Circuit
f
L = R
c
= R
L
L
/ 2πL
/ 2πf
c
= 8Ω / 2π * 20kHz = 64μH
PP, August 2009, Rev 3.1
Pre-Production
108