bd5445efv ROHM Co. Ltd., bd5445efv Datasheet - Page 14

• Manufacturer Part Number: bd5445efv
• Description: Analog Input / Single End Output Class-d Speaker Amplifier
• Manufacturer: ROHM Co. Ltd.

●Output LC Filter Circuit (Pins 17, 18, 25, and 26)
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BD5445EFV
www.rohm.com
An output filter is required to eliminate radio-frequency components exceeding the audio-frequency region supplied to a load
(speaker). Because this IC uses sampling clock between 480kHz and 720kHz in the output PWM signals, the high-frequency
components must be appropriately removed.
This section takes an example of an LC type LPF, in which coil L
attenuation property of -12dB/oct. A large part of switching currents flow to capacitor C
flow to speaker R
In SE(single end) applications, the dc blocking capacitor (Cse) and speaker impedance compose the primary HPF. The cutoff
frequency is determined by
The following table is Cse setting at cutoff frequency 20Hz, 40Hz, and 60Hz.
Fig.30 SE filter configuration
BTL output
SE output
Speaker
R
4Ω
6Ω
8Ω
L
L
. The following is a table for output LC filter constants.
C f
=
fc=60Hz
2πC
680
470
330
4Ω
6Ω
8Ω
4Ω
6Ω
8Ω
R
L
SE
1
•
R
L
[ ]
Hz
Fig.31 BTL filter configuration
fc=40Hz
L
C
fil
1000
SE
680
470
[μH]
22
33
47
15
22
33
[μF]
14/31
C
fc=20Hz
fil1
2200
1500
1000
0.68
0.47
0.39
0.22
0.15
0.1
[μF]
fil
and capacitor C
C
fil2
0.68
0.47
―
―
―
[μF]
1
fil
fil
, and only a small part of the currents
compose a differential filter with an
Technical Note
2010.05 - Rev.B