19-1710; Rev 0; 4/00
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
General Description
The MAX7426/MAX7427 5th-order, lowpass, elliptic,
switched-capacitor filters (SCFs) operate from a single
+5V (MAX7426) or +3V (MAX7427) supply. The devices
draw only 0.8mA of supply current and allow corner fre-
quencies from 1Hz to 12kHz, making them ideal for
low-power post-DAC filtering and anti-aliasing applica-
tions. They can be put into a low-power mode, reducing
supply current to 0.2µA.
Two clocking options are available: self-clocking (through
the use of an external capacitor) or external clocking for
tighter cutoff-frequency control. An offset-adjust pin
allows for adjustment of the DC output level.
The MAX7426/MAX7427 deliver 37dB of stopband
rejection and a sharp rolloff with a transition ratio of
1.25. Their fixed response limits the design task to
selecting a clock frequency.
o
5th-Order, Elliptic Lowpass Filters
o
Low Noise and Distortion: -80dB THD + Noise
o
Clock-Tunable Corner Frequency (1Hz to 12kHz)
o
Single-Supply Operation
+5V (MAX7426)
+3V (MAX7427)
o
Low Power
0.8mA (Operating Mode)
0.2µA (Shutdown Mode)
o
Available in 8-Pin µMAX/PDIP Packages
o
Low Output Offset: ±4mV
Features
MAX7426/MAX7427
Applications
ADC Anti-Aliasing
Post-DAC Filtering
CT2 Base Stations
Speech Processing
PART
MAX7426CUA
MAX7426CPA
MAX7426EUA
MAX7426EPA
MAX7427CUA
MAX7427CPA
MAX7427EUA
MAX7427EPA
Ordering Information
TEMP. RANGE
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
8 µMAX
8 Plastic DIP
8 µMAX
8 Plastic DIP
8 µMAX
8 Plastic DIP
8 µMAX
8 Plastic DIP
Selector Guide
PART
MAX7426
MAX7427
TRANSITION RATIO
r = 1.25
r = 1.25
OPERATING
VOLTAGE (V)
+5
+3
Typical Operating Circuit
V
SUPPLY
Pin Configuration
TOP VIEW
0.1µF
V
DD
INPUT
IN
SHDN
OUT
OUTPUT
COM
1
IN
2
GND
COM
GND
OS
0.1µF
3
8
7
CLK
SHDN
OS
OUT
MAX7426
MAX7427
CLOCK
CLK
MAX7426
MAX7427
6
5
V
DD
4
µMAX/PDIP
________________________________________________________________
Maxim Integrated Products
1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
MAX7426/MAX7427
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND ..............................................................-0.3V to +6V
IN, OUT, COM, OS, CLK,
SHDN
................-0.3V to (V
DD
+ 0.3V)
OUT Short-Circuit Duration.......................................................1s
Continuous Power Dissipation (T
A
= +70°C)
8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW
8-Pin PDIP (derate 6.90mW/°C above +70°C).............552mW
Operating Temperature Ranges
MAX742 _C_A ....................................................0°C to +70°C
MAX742 _E_A .................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
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—MAX7426
(V
DD
= +5V, filter output measured at OUT, 10kΩ
||
50pF load to GND at OUT,
SHDN
= V
DD
, OS = COM, 0.1µF from COM to GND,
f
CLK
= 100kHz, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
FILTER
Corner-Frequency Range
Clock-to-Corner Ratio
Clock-to-Corner Tempco
Output Voltage Range
Output Offset Voltage
DC Insertion Gain with Output
Offset Removed
Total Harmonic Distortion plus
Noise
Offset Voltage Gain
THD+N
A
OS
V
OFFSET
V
IN
= V
COM
= V
DD
/ 2
V
COM
= V
DD
/ 2 (Note 2)
f
IN
= 200Hz, V
IN
= 4Vp-p,
measurement bandwidth = 22kHz
OS to OUT
Input, COM externally driven
COM Voltage Range
V
COM
Output, COM internally driven
Input Voltage Range at OS
Input Resistance at COM
Clock Feedthrough
Resistive Output Load Drive
Maximum Capacitive Load
at OUT
Input Leakage Current at COM
Input Leakage Current at OS
CLOCK
Internal Oscillator Frequency
Clock Output Current
(internal oscillator mode)
Clock Input High
Clock Input Low
f
OSC
I
CLK
V
IH
V
IL
4.5
0.5
C
OSC
= 1000pF (Note 3)
13.5
17.5
±8
21.5
±12.5
kHz
µA
V
V
R
L
C
L
SHDN
= GND, V
COM
= 0 to V
DD
V
OS
= 0 to V
DD
V
OS
R
COM
T
A
= +25°C
10
50
Measured with respect to COM
90
V
DD
- 0.5
2
V
DD
- 0.2
2
0
0.25
±4
0.2
-81
+1
V
DD
2
V
DD
2
±0.1
130
5
1
500
±0.2
±0.2
±10
±10
V
DD
+ 0.5
2
V
V
DD
+ 0.2
2
V
kΩ
mVp-p
kΩ
pF
µA
µA
f
C
f
CLK
/f
C
(Note 1)
0.001 to 9
100:1
10
V
DD
- 0.25
±25
0.4
ppm/°C
V
mV
dB
dB
V/V
kHz
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
ELECTRICAL CHARACTERISTICS—MAX7426 (continued)
(V
DD
= +5V, filter output measured at OUT, 10kΩ
||
50pF load to GND at OUT,
SHDN
= V
DD
, OS = COM, 0.1µF from COM to GND,
f
CLK
= 100kHz, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
POWER REQUIREMENTS
Supply Voltage
Supply Current
Shutdown Current
Power-Supply Rejection Ratio
SHUTDOWN
SHDN
Input High
SHDN
Input Low
SHDN
Input Leakage Current
V
SDH
V
SDL
V
SHDN
= 0 to V
DD
±0.2
4.5
0.5
±10
V
V
µA
V
DD
I
DD
I
SHDN
PSRR
Operating mode, no load
SHDN
= GND
Measured at DC
4.5
0.8
0.2
70
5.5
1.0
1
V
mA
µA
dB
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX7426/MAX7427
ELECTRICAL CHARACTERISTICS—MAX7427
(V
DD
= +3V, filter output measured at OUT pin, 10kΩ
||
50pF load to GND at OUT,
SHDN
= V
DD
, OS = COM, 0.1µF from COM to
GND, f
CLK
= 100kHz, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
FILTER CHARACTERISTICS
Corner-Frequency Range
Clock-to-Corner Ratio
Clock-to-Corner Tempco
Output Voltage Range
Output Offset Voltage
DC Insertion Gain with Output
Offset Removed
Total Harmonic Distortion plus
Noise
Offset Voltage Gain
COM Voltage Range
Input Voltage Range at OS
Input Resistance at COM
Clock Feedthrough
Resistance Output Load Drive
Maximum Capacitive Load
at OUT
Input Leakage Current at COM
Input Leakage Current at OS
R
L
C
L
SHDN
= GND, V
COM
= 0 to V
DD
V
OS
= 0 to V
DD
THD+N
A
OS
V
COM
V
OS
R
COM
T
A
= +25°C
10
50
Measured with respect to COM
90
V
OFFSET
V
IN
= V
COM
= V
DD
/ 2
V
COM
= V
DD
/ 2 (Note 2)
f
IN
= 200Hz, V
IN
= 2.5Vp-p,
measurement bandwidth = 22kHz
OS to OUT
V
DD
- 0.1
2
0
0.25
±4
0.2
-79
+1
V
DD
2
±0.1
130
3
1
500
±0.2
±0.2
±10
±10
V
DD
+ 0.1
2
f
C
f
CLK/
f
C
(Note 1)
0.001 to 12
100:1
10
V
DD
- 0.25
±25
0.4
ppm/°C
V
mV
dB
dB
V/V
V
V
kΩ
mVp-p
kΩ
pF
µA
µA
kHz
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
_______________________________________________________________________________________
3
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
MAX7426/MAX7427
ELECTRICAL CHARACTERISTICS—MAX7427 (continued)
(V
DD
= +3V, filter output measured at OUT pin, 10kΩ
||
50pF load to GND at OUT,
SHDN
= V
DD
, OS = COM, 0.1µF from COM to
GND, f
CLK
= 100kHz, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
CLOCK
Internal Oscillator Frequency
Clock Output Current
(internal oscillator mode)
Clock Input High
Clock Input Low
POWER REQUIREMENTS
Supply Voltage
Supply Current
Shutdown Current
Power-Supply Rejection Ratio
SHUTDOWN
SHDN
Input High
SHDN
Input Low
SHDN
Input Leakage Current
V
SDH
V
SDL
V
SHDN
= 0 to V
DD
±0.2
2.5
0.5
±10
V
V
µA
V
DD
I
DD
I
SHDN
PSRR
Operating mode, no load
SHDN
= GND
Measured at DC
2.7
0.75
0.2
70
3.6
1.0
1
V
mA
µA
dB
f
OSC
I
CLK
V
IH
V
IL
C
OSC
= 1000pF (Note 3)
V
CLK
= 0 or 3V
2.5
0.5
13.5
17.5
±7.5
21.5
±12.5
kHz
µA
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ELLIPTIC FILTER CHARACTERISTICS (r = 1.25)
(V
DD
= +5V for MAX7426, V
DD
= +3V for MAX7427, filter output measured at OUT, 10kΩ
||
50pF load to GND at OUT,
SHDN
= V
DD,
V
COM
= V
OS
= V
DD
/ 2, f
CLK
= 100kHz, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 3)
PARAMETER
f
IN
= 0.38f
C
f
IN
= 0.68f
C
f
IN
= 0.87f
C
Insertion Gain
with DC Gain Error Removed
(Note 4)
f
IN
= 0.97f
C
f
IN
= f
C
f
IN
= 1.25f
C
f
IN
= 1.43f
C
f
IN
= 3.25f
C
CONDITIONS
MIN
-0.4
-0.4
-0.4
-0.4
-0.7
TYP
-0.2
0.2
-0.2
0.2
-0.2
-38.5
-37.2
-37.2
MAX
0.4
0.4
0.4
0.4
0.2
-34
-35
-35
dB
UNITS
Note 1:
The maximum f
C
is defined as the clock frequency f
CLK
= 100
✕
f
C
at which the peak SINAD drops to 68dB with a sinu-
soidal input at 0.2f
C
.
Note 2:
DC insertion gain is defined as
∆V
OUT
/
∆V
IN
.
Note 3:
f
OSC
(kHz)
≈
17.5
✕
10
3
/ C
OSC
(C
OSC
in pF).
Note 4:
The input frequencies, f
IN
, are selected at the peaks and troughs of the ideal elliptic frequency responses.
4
_______________________________________________________________________________________
5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters
MAX7426/MAX7427
Typical Operating Characteristics
(V
DD
= +5V for MAX7426, V
DD
= +3V for MAX7427, f
CLK
= 100kHz,
SHDN
= V
DD
, V
COM
= V
OS
= V
DD
/ 2, T
A
= +25°C, unless other-
wise noted.)
FREQUENCY RESPONSE
MAX7426/27-02
PASSBAND FREQUENCY RESPONSE
MAX7426/27-04
PHASE RESPONSE
-50
PHASE SHIFT (DEGREES)
-100
-150
-200
-250
-300
-350
-400
f
C
= 1kHz
r = 1.25
MAX7426/27-06
10
0
-10
GAIN (dB)
f
C
= 1kHz
r = 1.25
0.4
0.2
0
GAIN (dB)
-0.2
-0.4
-0.6
-0.8
-1.0
f
C
= 1kHz
r = 1.25
0
0.2
0.4
0.6
0.8
0
-20
-30
-40
-50
-60
-70
0
1
2
3
4
5
INPUT FREQUENCY (kHz)
1.0
0
0.2
0.4
0.6
0.8
1.0
1.2
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX7426/27-07
SUPPLY CURRENT vs. TEMPERATURE
0.86
0.84
SUPPLY CURRENT (mA)
0.82
0.80
0.78
0.76
0.74
0.72
0.70
V
DD
= +3V
V
DD
= +5V
MAX7426/27-08
0.82
0.80
SUPPLY CURRENT (mA)
0.78
0.76
0.74
0.72
0.70
2.5
3.0
3.5
4.0
4.5
5.0
0.88
0.68
5.5
-60
-40
-20
0
20
40
60
80
100
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
_______________________________________________________________________________________
5
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