LX1710-1 Microsemi Corporation, LX1710-1 Datasheet - Page 10

• Manufacturer Part Number: LX1710-1
• Description: EVALUATION KIT
• Manufacturer: Microsemi Corporation

LXE1710 E
evaluation board is a second order, LC type filter as
shown below.
component cost must be considered when determining
the complexity or type of filter selected.
Its Laplace Transform function is:
The Class-D amplifier evaluation board design has a
pass-band of 20Hz to 20kHz to support the audio
frequency range and is configured to utilize a switching
or oscillator frequency f
application, this oscillator frequency may be adjusted
(see section on Oscillator Configuration) to optimize
amplifier
considerations
requirements of the filter are that the pass band
attenuation of switching frequency f
than 40dB and the corner frequency of the LC filter
should be set higher than 20kHz to avoid attenuating
audio signals in the desired audio band by more than
1dB. A speaker DC impedance o
50kHz corner frequency are defined for the evaluation
board.
The Q (selectivity factor or ratio of the center
frequency divided by the bandwidth) of the filter must
also be considered when designing a filter. Too high a
Q will result in a boost of the audio signal across the
audio band whereas a low Q will cause too much
attenuation of the signal. A Q value of 0.707 provides
Copyright
Rev. 1.1, 2000-12-01
OUT+
OUT-
H(S)
Where
performance
2000
S
2
VALUATION
Tradeoffs between performance and
such
RC
1
L
L
C
S
Q
S
s
15µH
15µH
as
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
= 500kHz. Depending on the
RC
LC
or
LC
1
1
EMI
modified
S
B
effects.
2
s
OARD
C
0.68µF
C
0.68µF
should be lower
Q
C
S
S
for
Linfinity Microelectronics Division
Further
R
2
other
Microsemi
C
=
the required audio response and is used in the
calculation below.
Frequency response of the audio amplifier was
attenuation respectively.
frequency response performance for other loads, the
value of Q must be increased/decreased by changing
the capacitor. Since a different value C will affect the
corner frequency, values for L and C must be
recalculated. Below are recommended inductor and
capacitor values for 2
single stage LC filter design.

 
Please note:
for speaker loads.
impedances, which may require revised filter calculations
and optimization. Furthermore, your application may have
different design goals than those chosen for the LX1710
evaluation board
L
+15
+12.5
+10
+7.5
+5
+2.5
+0
-2.5
-5
-7.5
-10
-12.5
-15
10
C
C




1
2
C
L
20
Filter Component Values
. 0
R
Q
68
15
2 (
To Compute the Inductor Value:
µF
µH
50
LXE1710 Evaluation Board
These recommended values are guidelines
.
f
R
Capacitor C (µF)
1
C
is
Frequency Response
10
2 (
)
is
2
Q
used
C
used
f
20
C
0.68
0.47
1.0
)
Actual speakers have varying
in the
[(
in the
Frequency (Hz)
2
50
4
2 (
)(
Therefore, to improve
Evaluation
50000
1k
. 0
Evaluation
)(
707
50000
1
2k
U
)]
SER
Inductor L (µH)
2
5k
)
(.
68
Board
Board
. 0
10
k
G
) µ
10
15
22
56
UIDE
Page 10
20
k
µ
14
F




–4dB
.
µ 9
50
k
H
80
k