13
LTC1563-2/LTC1563-3
156323fa
Figure 5. 4th Order Filter Connections (Power Supply, Ground,
EN and LP Connections Not Shown for Clarity). Table 1 Shows
Resistor Values
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
LP
SA
NC
INVA
NC
LPA
AGND
V
–
V
+
LPB
NC
INVB
NC
SB
NC
EN
V
OUT
LTC1563-2
V
IN
1563 F05
R31
R32
R22
R21
R11
R12
4th Order Filter Responses Using the LTC1563-2
FREQUENCY (Hz)
0.1
GAIN (dB)
–20
–40
–60
–80
–90
10
0
101
1563 F05a
NORMALIZED TO f
C
= 1Hz
BUTTERWORTH
0.5dB RIPPLE
CHEBYSHEV
0.1dB RIPPLE
CHEBYSHEV
Figure 5a. Frequency Response
FREQUENCY (Hz)
0.1
GAIN (dB)
–2
–4
–6
–8
–10
1
0
21
1563 F05b
BUTTERWORTH
0.5dB RIPPLE
CHEBYSHEV
0.1dB RIPPLE
CHEBYSHEV
NORMALIZED TO f
C
= 1Hz
Figure 5b. Passband Frequency Response
TIME (s)
0
OUTPUT VOLTAGE (V)
1.2
1.0
0.8
0.6
0.4
0.2
0
1.00.5 1.5 2.0
1563 F05c
2.5 3.0
BUTTERWORTH
0.5dB RIPPLE
CHEBYSHEV
0.1dB RIPPLE
CHEBYSHEV
NORMALIZED TO f
C
= 1Hz
Figure 5c. Step Response
Table 1. Resistor Values, Normalized to 256kHz Cutoff Frequency (f
C
), Figure 5. The Passband
Gain, of the 4th Order LTC1563-2 Lowpass Filter, Is Set to Unity. (Note 1)
0.1dB RIPPLE 0.5dB RIPPLE
BUTTERWORTH CHEBYSHEV CHEBYSHEV
LP Mode Max f
C
25.6kHz 15kHz 13kHz
HS Mode Max f
C
256kHz 135kHz 113kHz
R11 = R21 = 10k(256kHz/f
C
) 13.7k(256kHz/f
C
) 20.5k(256kHz/f
C
)
R31 = 10k(256kHz/f
C
) 10.7k(256kHz/f
C
) 12.4k(256kHz/f
C
)
R12 = R22 = 10k(256kHz/f
C
) 10k(256kHz/f
C
) 12.1k(256kHz/f
C
)
R32 = 10k(256kHz/f
C
) 6.81k(256kHz/f
C
) 6.98k(256kHz/f
C
)
Example: In HS mode, 0.1dB ripple Chebyshev, 100kHz cutoff frequency, R11 = R21 = 35k ≅ 34.8k (1%),
R31 = 27.39k ≅ 27.4k (1%), R12 = R22 = 256k ≅ 255k (1%), R32 = 17.43k ≅ 17.4k (1%)
Note 1: The resistor values listed in this table provide good approximations of the listed transfer functions. For the
optimal resistor values, higher gain or other transfer functions, use FilterCAD Version 3.0 (or newer) or contact the
Linear Technology Filter Applications group for assistance.
APPLICATIONS INFORMATION
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