AN1013 데이터 시트보기 (PDF) - STMicroelectronics
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AN1013 Datasheet PDF : 13 Pages
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AN1013 APPLICATION NOTE
Figure 14
Attenuation (dB)
10
0
-10
-20
-30
-40
-50
-60
10
Rl=8ohm
100 1000 10000 100000
Frequency(Hz)
Figure 15
Attenuation (dB)
10
0
-10
-20
-30
Rl=4ohm
-40
-50
-60
10 10 1000 10000 100000
Frequency (Hz)
if a 4Ω loudspeaker was used without changing the filter components values, a high frequency loss
would be caused (fig.15), otherwise if a 16Ω loudspeaker was used, an high frequency peaking would
be caused (fig.16).
Figure 16
Attenuation (dB)
Figure 17
10
L1
0
-10
-20
Rl=16ohm
-30
C1
RL
-40
-50
-60
10
100 1000 10000 100000
Frequency (Hz)
Class-D Amplifier TDA7480/81/82
Appendix to the Application Note
As explained, it is quite important to correctly dimension the filter components value to obtain the best
performances from the application.
In the following section suggestions will be given for the right dimensioning. information
2 Pole Butterworth filter: (fig.17)
To avoid Underdamped or overdamped behaviour of the filter (fig.18) the amount of the ratio of induc-
tance to capacitance Q (quality factor) Q= Rload √C/L should be chosen between 0.6 ≤ Q ≤ 0.8, in our
application we used Q = 0.707 as god compromise that takes in account the impedance variation in
real loudspeakers.
The equations to be used to calculate the filter components values are the following:
L
=
1.414 ⋅
2π ⋅
Rload
Fc
[1]
C
=
2π
⋅
0.707
Fc ⋅ Rload
[2]
where: Fc=Cutoff frequency(30KHz;Rload=Loudspeakerimpedance)
Example: Fc = 30KHz,Rload = 8ohm
L
=
1.414 ⋅ 8
2π ⋅ 30 ⋅ 103
=
60µH
C
=
2π
⋅
0.707
30 ⋅ 103
⋅
8
=
0.47µF
10/13
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