MAXIM MAX7426, MAX7427 Technical data

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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 fre­quencies from 1Hz to 12kHz, making them ideal for
low-power post-DAC filtering and anti-aliasing applica­tions. 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.

Applications

ADC Anti-Aliasing CT2 Base Stations

Post-DAC Filtering Speech Processing

Features

♦ 5th-Order, Elliptic Lowpass Filters

♦ Low Noise and Distortion: -80dB THD + Noise

♦ Clock-Tunable Corner Frequency (1Hz to 12kHz)

♦ Single-Supply Operation

+5V (MAX7426)
+3V (MAX7427)

♦ Low Power

0.8mA (Operating Mode)

0.2µA (Shutdown Mode)

♦ Available in 8-Pin µMAX/PDIP Packages

♦ Low Output Offset: ±4mV

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

________________________________________________________________ Maxim Integrated Products 1

Typical Operating Circuit

19-1710; Rev 0; 4/00

Pin Configuration

Ordering Information

PART

MAX7426CUA

MAX7426CPA

MAX7426EUA -40°C to +85°C

0°C to +70°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

8 µMAX

8 Plastic DIP

8 µMAX

MAX7426EPA -40°C to +85°C 8 Plastic DIP

PART

TRANSITION RATIO

OPERATING

VOLTAGE (V)

MAX7426 r = 1.25 +5

Selector Guide

MAX7427 r = 1.25 +3

MAX7427CUA

MAX7427CPA

MAX7427EUA -40°C to +85°C

0°C to +70°C

0°C to +70°C 8 µMAX

8 Plastic DIP

8 µMAX

MAX7427EPA -40°C to +85°C 8 Plastic DIP

For free samples and the latest literature, visit www.maxim-ic.com or phone [phone].
For small orders, phone [phone].

87CLK

MAX7426
MAX7427

µMAX/PDIP

SHDNIN

OS

6

OUTV

5

0.1µF

INPUT

CLOCK

V

SUPPLY

V

DD

SHDN

IN

MAX7426
MAX7427

CLK

GND

OUT

COM

OUTPUT

OS

0.1µF

TOP VIEW

COM

GND

1

2

3

4

DD

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS—MAX7426

(VDD= +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, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°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.

VDDto 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

C

OSC

= 1000pF (Note 3)

VOS= 0 to V

DD

SHDN = GND, V

COM

= 0 to V

DD

(Note 1)

TA= +25°C

Input, COM externally driven

OS to OUT

Measured with respect to COM

fIN= 200Hz, VIN= 4Vp-p,
measurement bandwidth = 22kHz

VIN= V

COM

= V

DD

/ 2

V

COM

= V

DD

/ 2 (Note 2)

Output, COM internally driven

CONDITIONS

13.5 17.5 21.5f

OSC

Internal Oscillator Frequency

±0.2 ±10Input Leakage Current at OS

±0.2 ±10Input Leakage Current at COM

50 500C

L

10 1R

L

Resistive Output Load Drive

5Clock Feedthrough

90 130R

COM

Input Resistance at COM

±0.1V

OS

Input Voltage Range at OS

V

DD

- 0.2

V

DDVDD

+ 0.2

2 2 2

100:1f

CLK/fC

Clock-to-Corner Ratio

0.001 to 9f

C

Corner-Frequency Range

V

DD

- 0.5

V

DDVDD

+ 0.5

2 2 2

V

COM

COM Voltage Range

+1A

OS

Offset Voltage Gain

-81THD+N

Total Harmonic Distortion plus
Noise

10Clock-to-Corner Tempco

0.25 VDD- 0.25Output Voltage Range

±4 ±25V

OFFSET

Output Offset Voltage

0 0.2 0.4

DC Insertion Gain with Output
Offset Removed

MIN TYP MAXSYMBOLPARAMETER

0.5V

IL

Clock Input Low

4.5V

IH

Clock Input High

±8 ±12.5I

CLK

Clock Output Current
(internal oscillator mode)

V

V

µA

kHz

µA

µA

pF

kΩ

mVp-p

kΩ

V

V

V/V

dB

dB

mV

V

ppm/°C

kHz

UNITS

Maximum Capacitive Load
at OUT

FILTER

CLOCK

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

_______________________________________________________________________________________ 3

5th-Order, Lowpass, Elliptic,

Switched-Capacitor Filters

ELECTRICAL CHARACTERISTICS—MAX7426 (continued)

(VDD= +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, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS—MAX7427

(VDD= +3V, filter output measured at OUT pin, 10kΩ || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1µF from COM to
GND, f

CLK

= 100kHz, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

CONDITIONS

MIN TYP MAXSYMBOLPARAMETER

Measured at DC

SHDN = GND

Operating mode, no load

0.5V

SDL

SHDN Input Low

4.5V

SDH

SHDN Input High

70PSRRPower-Supply Rejection Ratio

0.2 1I

SHDN

Shutdown Current

0.8 1.0Supply Current I

DD

4.5 5.5V

DD

Supply Voltage

V

V

dB

µA

mA

V

UNITS

SHDN Input Leakage Current

V

SHDN

= 0 to V

DD

±0.2 ±10 µA

V

OS

Input Voltage Range at OS

90 130R

COM

Input Resistance at COM kΩ

(Note 1)

TA= +25°C

Measured with respect to COM

OS to OUT

fIN= 200Hz, VIN= 2.5Vp-p,
measurement bandwidth = 22kHz

VIN= V

COM

= V

DD

/ 2

V

COM

= V

DD

/ 2 (Note 2)

CONDITIONS

50 500C

L

10 1R

L

Resistance Output Load Drive

3Clock Feedthrough

±0.1

V

DD

- 0.1

V

DDVDD

+ 0.1

2 2 2

V

COM

COM Voltage Range

100:1f

CLK

/

f

C

Clock-to-Corner Ratio

0.001 to 12f

C

Corner-Frequency Range

+1A

OS

Offset Voltage Gain

-79THD+N

Total Harmonic Distortion plus
Noise

10Clock-to-Corner Tempco

0.25 VDD- 0.25Output Voltage Range

±4 ±25V

OFFSET

Output Offset Voltage

0 0.2 0.4

DC Insertion Gain with Output
Offset Removed

MIN TYP MAXSYMBOLPARAMETER

pF

kΩ

mVp-p

V

V

V/V

dB

dB

mV

V

ppm/°C

kHz

UNITS

Maximum Capacitive Load
at OUT

Input Leakage Current at COM

SHDN = GND, V

COM

= 0 to V

DD

±0.2 ±10 µA

Input Leakage Current at OS VOS= 0 to V

DD

±0.2 ±10 µA

POWER REQUIREMENTS

SHUTDOWN

FILTER CHARACTERISTICS

MAX7426/MAX7427

5th-Order, Lowpass, Elliptic,
Switched-Capacitor Filters

4 _______________________________________________________________________________________

C

OSC

= 1000pF (Note 3)

CONDITIONS

13.5 17.5 21.5f

OSC

Internal Oscillator Frequency

MIN TYP MAXSYMBOLPARAMETER

Measured at DC

SHDN = GND

Operating mode, no load

V

CLK

= 0 or 3V

0.5V

SDL

SHDN Input Low

2.5V

SDH

SHDN Input High

70PSRRPower-Supply Rejection Ratio

0.2 1I

SHDN

Shutdown Current

0.75 1.0

2.7 3.6V

DD

Supply Voltage

0.5V

IL

Clock Input Low

2.5V

IH

Clock Input High

±7.5 ±12.5I

CLK

Clock Output Current
(internal oscillator mode)

V

V

dB

µA

V

V

V

µA

kHz

UNITS

SHDN Input Leakage Current

V

SHDN

= 0 to V

DD

±0.2 ±10 µA

ELECTRICAL CHARACTERISTICS—MAX7427 (continued)

(VDD= +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, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

ELLIPTIC FILTER CHARACTERISTICS (r = 1.25)

(VDD= +5V for MAX7426, VDD= +3V for MAX7427, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, SHDN = V

DD,

V

COM

= V

OS =VDD

/ 2, f

CLK

= 100kHz, TA = T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)

Note 1: The maximum f

C

is defined as the clock frequency f

CLK

= 100 ✕fCat 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

/ ∆VIN.

Note 3: f

OSC

(kHz) ≈ 17.5 ✕103/ C

OSC(COSC

in pF).

Note 4: The input frequencies, f

IN

, are selected at the peaks and troughs of the ideal elliptic frequency responses.

f

IN

= 0.68f

C

fIN= 0.38f

C

fIN= 3.25f

C

fIN= 1.43f

C

fIN= 1.25f

C

fIN= 0.87f

C

fIN= 0.97f

C

fIN= f

C

CONDITIONS

-0.4 0.2 0.4

dB

-0.4 -0.2 0.4

Insertion Gain
with DC Gain Error Removed
(Note 4)

-37.2 -35

-37.2 -35

-38.5 -34

-0.4 -0.2 0.4

-0.4 0.2 0.4

-0.7 -0.2 0.2

UNITSMIN TYP MAXPARAMETER

mAI

DD

Supply Current

CLOCK

POWER REQUIREMENTS

SHUTDOWN