Datasheet

14
LTC1562
1562fa
TYPICAL APPLICATIONS
U
(Basic)
1
2
3
5
6
8
9
10
20
19
18
16
15
13
12
11
INV B
V1 B
V2 B
V
+
SHDN
V2 A
V1 A
INV A
INV C
V1 C
V2 C
V
–
AGND
V2 D
V1 D
INV D
LTC1562
R
IN2
R
IN4
R
IN1
V
IN2
V
IN1
SCHEMATIC INCLUDES PIN NUMBERS FOR 20-PIN PACKAGE.
PINS 4, 7, 14, 17 (NOT SHOWN) ALSO CONNECT TO V
–
V
OUT1
1562 TA03a
V
OUT2
R
IN3
–5V
5V
R
Q1
R21
R23
0.1µF
0.1µF
R
Q3
R24
R
Q4
R
Q2
R22
Dual 4th Order Lowpass Filters Amplitude Response
FREQUENCY (Hz)
10k
GAIN (dB)
10
0
–10
–20
–30
–40
–50
–60
–70
–80
100k 1M
1562 TA03b
BUTTERWORTH
f
–3dB
= 100kHz
10kR21, R23, R
IN1
, R
IN3
=
Quick Design Formulas for Some Popular Response Types:
2
100kHz
ƒ
C
Butterworth
(Maximally Flat Passband)
for f
C
10kHz to 140kHz
14.24k
2
100kHz
ƒ
C
Chebyshev
(Equiripple Passband)
for f
C
20kHz to 120kHz
3.951k
2
100kHz
ƒ
C
Bessel
(Good Transient Response)
for f
C
10kHz to 70kHz
5.412kR
Q1
, R
Q3
=
100kHz
ƒ
C
7.26k
100kHz
ƒ
C
5.066k
100kHz
ƒ
C
10kR22, R24, R
IN2
, R
IN4
=
2
100kHz
ƒ
C
7.097k
2
100kHz
ƒ
C
4.966k
2
100kHz
ƒ
C
13.07kR
Q2
, R
Q4
=
Notes: f
C
is the cutoff frequency: For Butterworth and Bessel, response is 3dB down at f
C
. For Chebyshev filters with
±0.1dB passband ripple up to 0.95 f
C
, use LTC1562 “A” grade.
Example: Butterworth response, f
C
= 50kHz. from the formulas above, R21 = R23 = R
IN1
= R
IN3
= 10k(100kHz/50kHz)
2
= 40k. R
Q1
= R
Q3
= 5.412k(100kHz/50kHz) = 10.82k. R22 = R24 = R
IN2
= R
IN4
= 10k(100kHz/50kHz)
2
= 40k.
R
Q2
= R
Q4
= 13.07k(100kHz/50kHz) = 26.14k. Use nearest 1% values.
100kHz
ƒ
C
17.53k
100kHz
ƒ
C
3.679k
100kHz
ƒ
C
1562 TA03 TABLE