Analog-Devices-Inc–Maxim-Integrated-MAX7425EUA-T
| Part # | Analog-Devices-Inc–Maxim-Integrated-MAX7425EUA-T |
Download  | Analog-Devices-Inc–Maxim-Integrated-MAX7425EUA-T |
5th-Order, Lowpass,
Switched-Capacitor Filters
MAX7418–MAX7425
General Description
Features
●
5th-Order, Lowpass Filters
The MAX7418–MAX7425 5th-order, low-pass, switched-
capacitor filters (SCFs) operate from a single +5V
(MAX7418–MAX7421) or +3V (MAX7422–MAX7425)
supply. These devices draw only 3mA of supply current
and allow corner frequencies from 1Hz to 45kHz, making
them ideal for low-power post-DAC filtering and anti-
aliasing applications. They feature a shutdown mode that
reduces supply current to 0.2μA.
• Elliptic
Response
(MAX7418/MAX7421/MAX7422/MAX7425)
• Bessel
Response (MAX7419/MAX7423)
• Butterworth
Response (MAX7420/MAX7424)
●
Clock-Turnable Corner Frequency (1Hz to 45kHz)
●
Single-Supply Operation
• +5V
(MAX7418–MAX7421)
• +3V
(MAX7422–MAX7425)
Two clocking options are available: self-clocking (through
the use of an external capacitor), or external clocking
for tighter corner-frequency control. An offset adjust pin
allows for adjustment of the DC output level.
●
Low Power
• 3mA
(Operating Mode)
•
0.2μA (Shutdown Mode)
The MAX7418/MAX7422 deliver 53dB of stopband
rejection and a sharp rolloff with a 1.6 transition ratio.
The MAX7421/MAX7425 achieve a sharper rolloff with a
1.25 transition ratio while still providing 37dB of stopband
rejection. The MAX7419/MAX7423 Bessel filters pro-
vide low overshoot and fast settling, and the MAX7420/
MAX7424 Butterworth filters provide a maximally flat
passband response. Their fixed response simplifies the
design task of selecting a clock frequency.
● Available
in 8-Pin μMAX Package
●
Low Output Offset: ±4mV
Ordering Information
PART
TEMP RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
8 μMAX
MAX7418
CUA
MAX7418EUA
MAX7419
CUA
MAX7419EUA
MAX7420
CUA
MAX7420EUA
MAX7421
CUA
MAX7421EUA
8 μMAX
8 μMAX
Applications
●
ADC Anti-Aliasing
● DAC
Postfiltering
8 μMAX
●
CT2 Base Stations
●
Speech Processing
8 μMAX
8 μMAX
Selector Guide
8 μMAX
OPERATING
VOLTAGE (V)
8 μMAX
PART
FILTER RESPONSE
Ordering Information continued at end of data sheet.
MAX7418
MAX7419
MAX7420
MAX7421
r = 1.6
Bessel
+5
+5
+5
+5
Typical Operating Circuit
Butterworth
r = 1.25
V
SUPPLY
Selector Guide continued at end of data sheet.
Pin Configuration
TOP VIEW
0.1µF
V
DD
SHDN
OUT
INPUT
IN
OUTPUT
MAX7418–
MAX7425
COM
IN
1
2
3
4
8
7
6
5
CLK
SHDN
OS
MAX7418–
MAX7425
CLOCK
CLK
COM
OS
GND
0.1µF
GND
V
DD
OUT
ꢀMAX
19-1821; Rev 2; 8/22
©
2022 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
One Analog Way, Wilmington, MA 01887 U.S.A.
T
e
l: 781.329.4700
© 2022
Analog Devices, Inc. All rights reserved.
|
|
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Absolute Maximum Ratings
V
to GND ……………………………………………………-0.3V to +6V
Operating
T
e
mperature Ranges
DD
IN, OU
T
,
C
OM, OS, CLK,
SHDN
…………. -0.3V to (V
OUT Short-Circuit Duration …………………………………………….. 1s
+ 0.3V)
MAX74 _ _C_A……………………………………………0°C to +70°C
MAX74 _ _E_
A
.
………………………………………. -40°C to +85°C
Junction
T
e
mperatur
e
.
…………………………………………….
.
+
150°C
Storage
T
e
mperature Rang
e
.
……………………… -65°C to +160°C
Lead
T
e
mperature (soldering, 10s) …………………………..
.
+
300°C
DD
Continuous Power Dissipation (T
= +70°C)
A
8-Pin μMAX (derate 4.1mW/°C above +70°C
)
…………
330mW
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Electrical Characteristics—MAX7418–MAX7421
(V
= +5
V
,
f
ilter output measured at OU
T
,
1
0kΩ || 50pF load to GND at OU
T
,
O
S = COM, 0.1μF capacitor from COM to GND,
DD
SHDN
= V
, f
= 2.2MHz, T
= T
to T
, unless otherwise noted. Typical values are at T
= +25°C.)
MAX A
DD CLK
A
MIN
PARAMETER
FILTER CHARACTERISTICS
Corner Frequency
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
f
V
= 4Vp-p (Note 1)
0.001 to 30
100:1
kHz
C
IN
Clock-to-Corner Ratio
Clock-to-Corner
T
e
mpco
Output Voltage Range
Output Offset Voltage
f
/ f
CLK C
10
ppm/°C
V
0.25
V
– 0.25
±25
DD
V
V
V
= V
= V
/ 2
DD
±4
0.2
0
mV
OFFSET
IN
COM
MAX7418/MAX7421
MAX7419/MAX7420
MAX7418
0
0.4
DC Insertion Gain with
Output Offset Removed
= V
/ 2
COM
DD
dB
dB
(Note 2)
-0.2
+0.2
-76
-78
-67
-78
1
f
= 2KHz,
IN
MAX7419
T
o
tal Harmonic Distortion
plus Noise
V
= 4Vp-p,
IN
THD+N
measurement
MAX7420
bandwidth = 80kHz
MAX7421
Offset Voltage Gain
A
OS to OUT
V/V
V
OS
Input, COM externally driven
Output, COM unconnected
Input, OS externally driven
2.0
2.3
2.5
2.5
3.0
2.7
COM Voltage Range
V
COM
Input Voltage Range at OS
Input Resistance at COM
Clock Feedthrough
V
V
±0.1
V
kΩ
OS
COM
R
100
140
COM
5
1
mVp-p
kΩ
Resistive Output Load Drive
R
C
10
50
L
Maximum Capacitive Output
Load Drive
500
pF
L
Input Leakage Current at COM
Input Leakage Current at OS
CLOCK
SHDN
= GND, V
= 0 to V
±0.1
±0.1
±10
±10
μA
μA
COM
DD
V
= 0 to V
DD
OS
MAX7418/MAX7421
MAX7419/MAX7420
MAX7418/MAX7421
MAX7419/MAX7420
68
86
87
106
135
±60
±75
C
= 1000pF
OSC
Internal Oscillator Frequency
f
kHz
OSC
(Note 3)
110
±40
±50
Clock Output Current
(Internal Oscillator Mode)
I
V
= 0 or 5V
μA
CLK
CLK
Clock Input High
Clock Input Low
V
4.5
V
V
IH
V
0.5
IL
Analog Devices
│
2
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Electrical Characteristics—MAX7418–MAX7421 (continued)
(V
= +5
V
,
f
ilter output measured at OU
T
,
1
0kΩ || 50pF load to GND at OU
T
,
O
S = COM, 0.1μF capacitor from COM to GND,
DD
SHDN
= V
, f
= 2.2MHz, T
= T
to T
, unless otherwise noted. Typical values are at T
= +25°C.)
MAX A
DD CLK
A
MIN
PARAMETER
POWER REQUIREMENTS
Supply Voltage
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
4.5
5.5
3.6
4.1
1
V
DD
MAX7418/MAX7421
MAX7418/MAX7421
2.9
3.4
0.2
70
Operating mode, no
Supply Current
I
mA
DD
load
Shutdown Current
I
SHDN
= GND
μA
SHDN
Power-Supply Rejection Ratio
SHUTDOWN
PSRR
IN = COM (Note 4)
dB
SHDN
Input High
V
4.5
V
V
SDH
SHDN
Input Low
V
0.5
SDL
SHDN
Input Leakage Current
V
= 0 to V
±0.2
±10
μA
SHDN
DD
Electrical Characteristics—MAX7422–MAX7425
(V
= +3
V
,
f
ilter output measured at OUT pin, 10kΩ || 50pF load to GND at OU
T
,
O
S = COM, 0.1μF capacitor from COM to GND,
DD
SHDN
= V
, f
= 2.2MHz, T
= T
to T
, unless otherwise noted. Typical values are at T
= +25°C.)
MAX A
DD CLK
A
MIN
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
FILTER CHARACTERISTICS
MAX7422/MAX7425
V
= 2.5Vp-p
IN
Corner-Frequency Range
f
100:1 to 45
kHz
C
(Note 1)
MAX7423/MAX7424
Clock-to-Corner Ratio
Clock-to-Corner
T
e
mpco
Output Voltage Range
Output Offset Voltage
f
/ f
100:1
10
CLK
C
ppm/°C
V
0.25
V
– 0.25
±25
DD
V
V
V
= V
= V
/ 2
DD
±4
0.2
0
mV
OFFSET
IN
COM
MAX7422/MAX7425
MAX7423/MAX7424
MAX7422
0
0.4
DC Insertion Gain with
Output Offset Removed
= V
/ 2
COM
DD
dB
dB
(Note 2)
-0.2
+0.2
-80
-81
-70
-80
1
f
= 2KHz,
= 2.5Vp-p,
IN
MAX7423
T
o
tal Harmonic Distortion
plus Noise
V
IN
THD+N
measurement
bandwidth = 80kHz
MAX7424
MAX7425
Offset Voltage Gain
A
OS to OUT
V/V
V
OS
Input, COM externally driven
Output, COM internally driven
Measured with respect to COM
1.4
1.4
1.5
1.5
1.6
1.6
COM Voltage Range
V
COM
Input Voltage Range at OS
Input Resistance at COM
Clock Feedthrough
V
V
±0.1
V
kΩ
OS
COM
R
100
140
COM
5
1
mVp-p
kΩ
Resistive Output Load Drive
R
C
10
50
L
Maximum Capacitive Load at
OUT
500
pF
L
Input Leakage Current at COM
Input Leakage Current at OS
SHDN
= GND, V
= 0 to V
±0.1
±0.1
±10
±10
μA
μA
COM
DD
V
= 0 to V
DD
OS
Analog Devices
│
3
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Electrical Characteristics—MAX7422–MAX7425 (continued)
(V
= +3
V
,
f
ilter output measured at OUT pin, 10kΩ || 50pF load to GND at OU
T
,
O
S = COM, 0.1μF capacitor from COM to GND,
DD
SHDN
= V
, f
= 2.2MHz, T
= T
to T
, unless otherwise noted. Typical values are at T
= +25°C.)
MAX A
DD CLK
A
MIN
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CLOCK
MAX7422/MAX7425
68
86
68
86
2.5
87
110
87
106
135
106
135
C
= 1000pF
OSC
Internal Oscillator Frequency
f
kHz
kHz
OSC
(Note 3)
V =
0 or 5V
CLK
MAX7423/MAX7424
MAX7422/MAX7425
MAX7423/MAX7424
Clock Output Current
(Internal Oscillator Mode)
I
CLK
110
Clock Input High
V
IH
Clock Input Low
V
0.5
IL
POWER REQUIREMENTS
Supply Voltage
V
2.7
3.6
3.4
3.8
1
V
DD
MAX7422/MAX7425
MAX7423/MAX7424
2.6
3.0
0.2
70
Operating mode, no
load
Supply Current
I
mA
DD
Shutdown Current
I
SHDN
= GND
μA
SHDN
Power-Supply Rejection Ratio
SHUTDOWN
PSRR
Measured at DC
dB
SHDN
Input High
V
4.5
V
V
SDH
SHDN
Input Low
V
0.5
SDL
SHDN
Input Leakage Current
V
= 0 to V
±0.2
±10
μA
SHDN
DD
Analog Devices
│
4
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Filter Characteristics
(V
= +5V for MAX7418-MAX7420, V
= +3V for MAX7422-MAX7425 filter output measured at OU
T
,
1
0kΩ || 50pF load to GND at
DD
DD
OU
T
,
SHDN
= V
, f
= 2.2MHz, T
= T
to T
, unless otherwise noted.)
DD CLK
A
MIN
MAX
PARAMETER
ELLIPTIC, R = 1.2—MAX7421/MAX7425
CONDITIONS
MIN
TYP
MAX
UNITS
f
f
f
f
f
f
f
f
= 0.38f
-0.4
-0.4
-0.4
-0.4
-0.7
-0.2
-0.2
-0.2
-0.2
-0.2
-36
0.4
0.4
0.4
0.4
0.2
-33
-35
-35
IN
IN
IN
IN
IN
IN
IN
IN
C
C
C
C
= 0.68f
= 0.87f
= 0.97f
Insertion Gain with DC Gain
Error Removed (Note 4)
dB
= f
C
= 1.25f
= 1.43f
= 3.25f
C
C
C
-37.2
-37.2
BESSEL FILTERS—MAX7419/MAX7423
f
f
f
f
= 0.5f
-1
-0.74
-3.0
IN
IN
IN
IN
C
= f
C
-3.6
-2.4
-35
-60
Insertion Gain Relative to
DC Gain
dB
dB
= 4f
= 7f
-41.0
-67
C
C
BUTTERWORTH FILTERS—MAX7420/MAX7424
f
f
f
f
= 0.5f
-3.0
-3.6
0
IN
IN
IN
IN
C
= f
C
-3.0
-47.5
-70
-2.4
-43
-65
Insertion Gain Relative to
DC Gain
= 3f
= 5f
C
C
Note 1:
The maximum f
is defined as the clock frequency f
= 100 x f
at which the peak S / (THD+N) drops to 68dB with a
C
C
CLK
sinusoidal input at 0.2f
. Maximum f
increases as V
signal amplitude decreases.
C
C
OUT
IN
Note 2:
DC insertion gain is defined as ΔV
/ ΔV
.
IN
3
Note 3:
MAX7418/MAX7421/MAX7422/MAX7425: f
(kHz)
≅
87×10 /
C
(pF).
OSC
OSC
OSC
3
MAX7419/MAX7420/MAX7423/MAX7424: f
(kHz)
≅
110×10 /
C
(pF).
OSC
Note 4:
PSRR is the change in output voltage from a V
of 4.5V and a V
of 5.5
V
.
DD
DD
Analog Devices
│
5
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Typical Operating Characteristics
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425; f
= 2.2MHz;
SHDN
= V
; V
= V
= V
/ 2;
DD
DD
CLK
DD COM
OS
DD
T =
+25°C; unless otherwise noted.)
A
MAX7419/MAX7423
FREQUENCY RESPONSE (BESSEL)
MAX7418/MAX7422
FREQUENCY RESPONSE (ELLIPTIC, R = 1.6)
MAX7420/MAX7424
FREQUENCY RESPONSE (BUTTERWORTH)
10
10
0
10
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
0
-10
-20
-30
-40
-50
-60
-70
-80
-10
-20
-30
-40
-50
-60
0
20
40
60
80
100
0
0
0
20
40
60
80
100
0
20
40
60
80
100
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
MAX7418/MAX7422
MAX7419/MAX7423
PASSBAND FREQUENCY RESPONSE
(ELLIPTIC, R = 1.6)
PASSBAND FREQUENCY RESPONSE
(BESSEL)
MAX7421/MAX7425
FREQUENCY RESPONSE (ELLIPTIC, R = 1.25)
10
0.4
0.2
0.5
0
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
0
-0.2
-0.4
-0.6
-0.8
-1.0
0
20
40
60
80
100
4.5
9.0
13.5
18.0
22.5
0
4.5
9.0
13.5
18.0
22.5
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
MAX7421/MAX7425
MAX7420/MAX7424
PASSBAND FREQUENCY RESPONSE
(ELLIPTIC, R = 1.25)
MAX7418/MAX7422
PASSBAND FREQUENCY RESPONSE
(BUTTERWORTH)
PHASE RESPONSE (ELLIPTIC, R = 1.6)
0.5
0.4
0.2
0
-50
0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
-100
-150
-200
-250
-300
-350
-400
-450
0
-0.2
-0.4
-0.6
-0.8
-1.0
0
4.5
9.0
13.5
18.0
22.5
4.5
9.0
13.5
18.0
22.5
0
4
8
12
16
20
24
28
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
Analog Devices
│
6
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Typical Operating Characteristics (continued)
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425; f
= 2.2MHz;
SHDN
= V
; V
= V
= V
/ 2;
DD
DD
CLK
DD COM
OS
DD
T =
+25°C; unless otherwise noted.)
A
MAX7419/MAX7423
PHASE RESPONSE (BESSEL)
MAX7424/MAX7425
PHASE RESPONSE (ELLIPTIC, R = 1.25)
MAX7420/MAX7424
PHASE RESPONSE (BUTTERWORTH)
0
0
-50
0
-50
-50
-100
-150
-200
-250
-100
-150
-200
-250
-300
-350
-400
-450
-100
-150
-200
-250
-300
-350
0
4
8
12
16
20
24
28
0
4
8
12
16
20
24
28
0
4
8
12
16
20
24
28
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
MAX7418
MAX7419
MAX7420
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(ELLIPTIC, R = 1.6)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(BESSEL)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(BUTTERWORTH)
0
0
0
SEE TABLE A
SEE TABLE A
SEE TABLE A
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
D
D
D
E
3
E
1
E
1
0
1
2
4
5
0
2
3
4
5
0
2
3
4
5
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
MAX7421
MAX7423
MAX7422
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(ELLIPTIC, R = 1.25)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(BESSEL)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(ELLIPTIC, R = 1.6)
0
0
0
SEE TABLE A
SEE TABLE A
SEE TABLE A
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
A
A
D
B
B
C
0.5
E
1
C
0
2
3
4
5
0
0.5
1.0
1.5
2.0
2.5
3.0
0
1.0
1.5
2.0
2.5
3.0
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
Analog Devices
│
7
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Typical Operating Characteristics (continued)
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425; f
= 2.2MHz;
SHDN
= V
; V
= V
= V
/ 2;
DD
DD
CLK
DD COM
OS
DD
T =
+25°C; unless otherwise noted.)
A
MAX7424
MAX7425
INTERNAL OSCILLATOR FREQUENCY
vs. SMALL CAPACITANCE (pF)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(BUTTERWORTH)
THD + NOISE vs. INPUT SIGNAL AMPLITUDE
(ELLIPTIC, R = 1.25)
0
0
7000
6000
5000
4000
3000
2000
1000
0
SEE TABLE A
SEE TABLE A
-10
-20
-30
-40
-50
-60
-70
-80
-90
-10
-20
-30
-40
-50
-60
-70
-80
-90
BESSEL/BUTTERWORTH
ELLIPTIC
A
B
A
B
C
C
0
0.5
1.0
1.5
2.0
2.5
3.0
0
0.5
1.0
1.5
2.0
2.5
3.0
1
10
100
1000
10000
AMPLITUDE (Vp-p)
AMPLITUDE (Vp-p)
CAPACITANCE ( pF)
ELLIPTIC INTERNAL OSCILLATOR
FREQUENCY vs. SUPPLY VOLTAGE
INTERNAL OSCILLATOR FREQUENCY
vs. LARGE CAPACITANCE (nF)
ELLIPTIC INTERNAL OSCILLATOR
FREQUENCY vs. TEMPERATURE
6
87.0
86.5
86.0
85.5
85.0
84.5
84.0
87.0
86.5
86.0
85.5
85.0
84.5
84.0
V
DD
= 3V
5
4
3
2
1
0
BESSEL/BUTTERWORTH
V
DD
= 5V
ELLIPTIC
C
OSC
= 1000PF
C
= 1000PF
-15
OSC
10
100
1000
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
10
35
60
85
CAPACITANCE (nF)
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
ELLIPTIC SUPPLY CURRENT
vs. TEMPERATURE
ELLIPTIC SUPPLY CURRENT
vs. SUPPLY VOLTAGE
3.3
3.1
2.9
2.7
2.5
2.3
3.0
2.9
2.8
2.7
2.6
2.5
Table A.
f
f
f
BW
IN
C
CLK
LABEL
V
= 5V
DD
(kHz) (kHz) (kHz) (kHz)
A
B
C
D
E
2
2
1
2
1
30
22
10
22
10
3000
2200
1000
2200
1000
80
80
22
80
22
V
DD
= 3V
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
-15
10
35
60
85
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
Analog Devices
│
8
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Typical Operating Characteristics (continued)
(V
= +5V for MAX7418–MAX7421, V
= +3V for MAX7422–MAX7425; f
= 2.2MHz;
SHDN
= V
; V
= V
= V
/ 2;
DD
DD
CLK
DD COM
OS
DD
T =
+25°C; unless otherwise noted.)
A
DC OFFSET VOLTAGE
vs. TEMPERATURE
DC OFFSET VOLTAGE
vs. SUPPLY VOLTAGE
3.0
2.5
2.0
1.5
1.0
0.5
0
2.5
2.0
1.5
1.0
0.5
0
V
= 5V
DD
V
DD
= 3V
-40
-15
10
35
60
85
2.5
3.0
3.5
4.0
4.5
5.0
5.5
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
Pin Description
PIN
NAME
FUNCTION
Common Input Pin. Biased internally at midsupply. Bypass COM externally to GND with a 0.1μF capacitor.
T
o
override internal biasing, drive COM with an external supply.
1
COM
2
3
IN
Filter Input
Ground
GND
Positive Supply Input: +5V for MAX7418–MAX7421, +3V for MAX7422–MAX7425. Bypass V
0.1μF capacitor.
to GND with a
DD
4
5
V
DD
OUT
OS
Filter Output
Offset Adjust Input.
T
o
a
djust output offset, connect OS to an external supply through a resistive voltage-
divider (Figure 4). Connect OS to COM if no offset adjustment is needed. The
Offset and Common-Mode
Input Adjustment
section.
6
7
8
SHDN
Shutdown Input. Drive low to enable shutdown mode; drive high or connect to V
for normal operation.
DD
Clock Input. Connect an external capacitor (C
) from CLK to ground.
T
o
o
verride the internal oscillator,
OSC
CLK
connect CLK to an external clock: f
= f
/100.
C
CLK
zero pairs, and the sections can be cascaded to produce
higher order filters. The advantage to this approach is
ease of design. However, this type of design is highly sen-
sitive to component variations if any section’s Q is high.
The MAX7418–MAX7425 use an alternative approach,
which is to emulate a passive network using switched-
capacitor integrators with summing and scaling. The pas-
sive network may be synthesized using CAD programs, or
may be found in many filter books. Figure 1 shows a basic
5th-order ladder filter structure.
Detailed Description
The MAX7418/MAX7421/MAX7422/MAX7425 elliptic
lowpass filters provide sharp rolloff with good stopband
rejection. The MAX7419/MAX7423 Bessel filters pro-
vide low overshoot and fast settling responses, and the
MAX7420/MAX7424 Butterworth filters provide a maxi-
mally flat passband response. All parts operate with a
100:1 clock-to-corner frequency ratio.
Most switch capacitor filters (SCFs) are designed with
biquadratic sections. Each section implements two pole-
Analog Devices
│
9
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Bessel Characteristics
Lowpass Bessel filters such as the MAX7419/MAX7423
delay all frequency components equally, preserving the
line up shape of step inputs (subject to the attenuation
of the higher frequencies). Bessel filters settle quickly—
an important characteristic in applications that use a
multiplexer (mux) to select an input signal for an analog-
to-digital converter (ADC). An anti-aliasing filter placed
between the mux and the ADC must settle quickly after a
new channel is selected.
R
S
L2
L4
+
–
C1
V
IN
C3
C5
R
L
Figure 1. 5th-Order Ladder Filter Network
An SCF that emulates a passive ladder filter retains many
of the same advantages. The component sensitivity of a
passive ladder filter is low when compared to a cascaded
biquadratic design because each component affects the
entire filter shape rather than a single pole-zero pair. In
other words, a mismatched component in a biquadratic
design has a concentrated error on its respective poles,
while the same mismatch in a ladder filter design spreads
its error over all poles.
Butterworth Characteristics
Lowpass Butterworth filters such as the MAX7420/
MAX7424 provide a maximally flat passband response,
making them ideal for instrumentation applications that
require minimum deviation from the DC gain throughout
the passband.
The difference between Bessel and Butterworth filters can
be observed when a 1kHz square wave is applied to the
filter input (Figure 3, trace A). With the filter cutoff frequen
–
cies set at 5kHz, trace B shows the Bessel filter response
and trace C shows the Butterworth filter response.
Elliptic Characteristics
Lowpass elliptic filters such as the MAX7418/MAX7421/
MAX7422/MAX7425 provide the steepest possible
rolloff with frequency of the four most common filter types
(Butterworth, Bessel, Chebyshev, and elliptic). The high-
Q value of the poles near the passband edge combined
with the stopband zeros allow for the sharp attenuation
characteristic of elliptic filters, making these devices ideal
for anti-aliasing and post-DAC filtering in single-supply
systems (see
Anti-Aliasing and Post-DAC Filtering
).
Clock Signal
External Clock
These SCFs are designed for use with external clocks
that have a 40% to 60% duty cycle. When using an exter
–
nal clock, drive the CLK pin with a CMOS gate powered
from 0 to V
. Varying the rate of the external clock
DD
adjusts the corner frequency of the filter.
In the frequency domain, the first transmission zero
causes the filter’s amplitude to drop to a minimum level
(Figure 2). Beyond this zero, the response rises as the
frequency increases until the next transmission zero.
f
CLK
100
f
=
C
The stopband begins at the stopband frequency, f . At
S
frequencies above f , the filter’s gain does not exceed
S
RIPPLE
the gain at f
. The corner frequency, f
, is defined as the
S
C
point at which the filter output attenuation falls just below
the passband ripple. The transition ratio (r) is defined
as the ratio of the stopband frequency to the corner
frequency:
f
C
f
f
S
C
TRANSITION RATIO =
f
S
r = f
/ f
S
C
The MAX7418/MAX7422 have a transition ratio of 1.6
and typically 53dB of stopband rejection. The MAX7421/
MAX7425 have a transition ratio of 1.25 (providing a
steeper rolloff) and typically 37dB of stopband rejection.
PASSBAND
STOPBAND
FREQUENCY
f
C
f
S
Figure 2. Elliptic Filter Response
Analog Devices
│
10
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
V
SUPPLY
2V/div
0.1µF
A
B
C
V
DD
SHDN
OUT
OUTPUT
2V/div
2V/div
INPUT
IN
COM
0.1µF
0.1µF
50k
MAX7418–
MAX7425
50k
50k
CLOCK
CLK
OS
200µs/div
GND
A: 1kHz INPUT SIGNAL
B: MAX7419 BESSEL FILTER RESPONSE; f
= 5kHz
C
C: MAX7420 BUTTERWORTH FILTER RESPONSE; f
= 5kHz
C
Figure 3. Bessel vs. Butterworth Filter Response
Figure 4. Offset Adjustment Circuit
Estimate the input impedance of the filter by using the
following formula:
Internal Clock
When using the internal oscillator, the capacitance (C
)
OSC
on CLK determines the oscillator frequency:
1
Z
=
IN
(f
×
C
)
IN
k
CLK
f
(kHz)
=
OSC
C
(pF)
OSC
where f
= clock frequency and C
= 1p
F
.
IN
CLK
where
k=87×10 for
the
MAX7418/MAX7421/MAX7422/MAX7425
and
Low-Power Shutdown Mode
3
The MAX7418–MAX7425 have a shutdown mode that is
activated by driving
SHDN
low. In shutdown mode, the
filter supply current reduces to 0.2μA, and the output of
the filter becomes high impedance. For normal operation,
3
k=110X10 for
the
drive
SHDN
high or connect to V
.
DD
MAX7419/MAX7420/MAX7423/ MAX7424.
Since C
is in the low picofarads, minimize the stray
OSC
Applications Information
capacitance at CLK so that it does not affect the inter-
nal oscillator frequency. Varying the rate of the internal
oscillator adjusts the filter’s corner frequency by a 100:1
clock-to-corner frequency ratio. For example, an internal
oscillator frequency of 2.2MHz produces a nominal corner
frequency of 22kHz.
Offset (OS) and Common-Mode (COM)
Input Adjustment
COM sets the common-mode input voltage and is biased
at midsupply with an internal resistor-divider. If the appli-
cation does not require offset adjustment, connect OS
to COM. For applications in which offset adjustment
is required, apply an external bias voltage through a
resistor-divider network to OS, as shown in Figure 4. For
applications that require DC level shifting, adjust OS with
respect to COM. (
Note:
Do not leave OS unconnected.)
The output voltage is represented by these equations:
Input Impedance vs. Clock Frequencies
The MAX7418–MAX7425s’ input impedance is effectively
that of a switched-capacitor resistor (see the following
equation), and is inversely proportional to frequency.
The input impedance values determined by the equation
represent the average input impedance, since the input
current is not continuous. As a rule, use a driver with
an output resistance less than 10% of the filter’s input
impedance.
V
=
( V
−
V
)
+
V
COM OS
OUT
IN
V
DD
V
=
(
t
ypica
l
)
COM
2
where (V
– V
) is lowpass filtered by the SCF and
IN
COM
OS is added at the output stage. See the
Electrical
Analog Devices
│
11
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Characteristics
table for the input voltage range of COM
and OS. Changing the voltage on COM or OS significantly
from midsupply reduces the dynamic range.
V+
Power Supplies
The MAX7418–MAX7421 operate from a single +5V sup-
ply and the MAX7422–MAX7425 operate from a single
*
V
DD
SHDN
OUT
OUTPUT
+3V supply. Bypass V
to GND with a 0.1μF capacitor.
DD
INPUT
IN
COM
If dual supplies are required, connect COM to the system
ground and GND to the negative supply. Figure 5 shows
an example of dual-supply operation. Single-supply and
dual-supply performance are equivalent. For either single-
supply or dual-supply operation, drive CLK and
SHDN
MAX7418–
MAX7425
V+
V-
CLOCK
CLK
OS
0.1µF
0.1µF
from GND (V- in dual supply operation) to V
. Use the
DD
GND
V-
MAX7418–MAX7421 for ±2.5, and use the MAX7422–
MAX7425 for ±1.5
V
.
F
or ±5V dual-supply applications,
refer to the MAX291/MAX292/MAX295/MAX296 and
MAX293/MAX294/MAX297 data sheets.
*CONNECT SHDN TO V- FOR LOW-POWER SHUTDOWN MODE.
Figure 5. Dual-Supply Operation
Input Signal Amplitude Range
The optimal input signal range is determined by observ-
ing the voltage level at which the signal-to-noise plus
distortion (SINAD) ratio is maximized for a given corner
frequency. The
Typical Operating Characteristics
show
the THD + Noise response as the input signal’s peak-to-
peak amplitude is varied.
Harmonic Distortion
Harmonic distortion arises from nonlinearities within the
filter. These nonlinearities generate harmonics when a
pure sine wave is applied to the filter input.
T
a
bles 1, 2,
and 3 list typical harmonic distortion values with a 10kΩ
Anti-Aliasing and Post-DAC Filtering
load at T
= +25°C.
A
When using the MAX7418–MAX7425 for anti-aliasing or
post-DAC filtering, synchronize the DAC (or ADC) and
the filter clocks. If the clocks are not synchronized, beat
frequencies may alias into the desired passband.
Table 1. MAX7418/MAX7421/MAX7422/MAX7425 Typical Harmonic Distortion
TYPICAL HARMONIC DISTORTION (dB)
f
f
V
IN
(Vp-p)
CLK
IN
FILTER
MAX7418
MAX7421
MAX7422
MAX7425
(MHz)
(kHz)
2nd
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
3rd
4th
5th
2.2
1.5
2.2
1.5
4.0
2.2
4.0
2.2
2
2
2
2
4
2
4
2
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
4
4
2
2
Analog Devices
│
12
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Table 2. MAX7420/MAX7424 Typical Harmonic Distortion
TYPICAL HARMONIC DISTORTION (dB)
f
f
V
IN
(Vp-p)
CLK
IN
FILTER
MAX7420
MAX7424
(MHz)
(kHz)
2nd
-77
3rd
-67
-70
-70
-77
4th
5th
-76
2.2
1.5
3.5
2.2
2
2
3
2
<-80
<-80
<-80
<-80
4
<-80
<-80
<-80
<-80
<-80
<-80
2
Table 3. MAX7419/MAX7423 Typical Harmonic Distortion
TYPICAL HARMONIC DISTORTION (dB)
f
f
V
IN
(Vp-p)
CLK
IN
FILTER
MAX7419
MAX7423
(MHz)
(kHz)
2nd
<-80
<-80
<-80
<-80
3rd
-77
4th
5th
2.2
1.5
3.5
2.2
2
2
3
2
<-80
<-80
<-80
<-80
<-80
<-80
<-80
<-80
4
-80
-75
2
<-80
Ordering Information (continued)
Selector Guide (continued)
PART
TEMP RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
OPERATING
VOLTAGE (V)
PART
FILTER RESPONSE
MAX7422
CUA
MAX7422EUA
MAX7423
CUA
MAX7423EUA
MAX7424
CUA
MAX7424EUA
MAX7425
CUA
MAX7425EUA
8 μMAX
MAX7422
MAX7423
MAX7424
MAX7425
r = 1.6
Bessel
+3
+3
+3
+3
8 μMAX
8 μMAX
Butterworth
r = 1.25
8 μMAX
8 μMAX
8 μMAX
8 μMAX
8 μMAX
Chip Information
TRANSISTOR COUN
T
:
1
457
PROCESS: BiCMOS
Analog Devices
│
13
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Package Information
For the latest package outline information and land patterns (footprints), go to
www.maximintegrated.com/packages
. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
α
α
Analog Devices
│
14
MAX7418–MAX7425
5th-Order, Lowpass,
Switched-Capacitor Filters
Revision History
REVISION REVISION
PAGES
CHANGED
DESCRIPTION
NUMBER
DATE
11/00
4/22
0
1
2
Initial release
—
5
Updated
Filter Characteristics
table
Updated
Internal Clock
section
8/22
11
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is
assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that
may result from its use.Specifications subject to change without notice. No license is granted by implicationor
otherwise under any patent or patent rights of Analog Devices. Trademarks andregistered trademarks are the
property of their respective owners.
Analog Devices
│
15
