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General Description

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, mak-

ing them ideal for low-power post-DAC filtering and anti-

aliasing applications. They feature a shutdown mode

that reduces supply current to 0.2µA.

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.

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 stop-

band rejection. The MAX7419/MAX7423 Bessel filters

provide low overshoot and fast settling, and the

MAX7420/MAX7424 Butterworth filters provide a maxi-

mally flat passband response. Their fixed response sim-

plifies the design task of selecting a clock frequency.

Applications

ADC Anti-Aliasing CT2 Base Stations

DAC Postfiltering Speech Processing

Features

♦ 5th-Order, Lowpass Filters

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)

♦ Low Power

3mA (Operating Mode)

0.2µA (Shutdown Mode)

♦ Available in 8-Pin µMAX Package

♦ Low Output Offset: ±4mV

MAX7418–MAX7425

5th-Order, Lowpass,

Switched-Capacitor Filters

________________________________________________________________ Maxim Integrated Products 1

OUTV

CLK

SHDNIN

GND

COM

µMAX

TOP VIEW

MAX7418–

MAX7425

CLK

OUT

GND

INPUT

0.1µF

CLOCK

SHDN

OUTPUT

SUPPLY

COM

MAX7418–

MAX7425

Typical Operating Circuit

19-1821; Rev 0; 11/00

Pin Configuration

Ordering Information

Selector Guide

PART

MAX7418EUA -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

8 µMAX

Selector Guide continued at end of data sheet.

Ordering Information continued at end of data sheet.

MAX7418CUA

0°C to +70°C 8 µMAX

MAX7419CUA

0°C to +70°C 8 µMAX

MAX7419EUA -40°C to +85°C 8 µMAX

MAX7420CUA

0°C to +70°C 8 µMAX

MAX7420EUA -40°C to +85°C 8 µMAX

MAX7421CUA

0°C to +70°C 8 µMAX

MAX7421EUA -40°C to +85°C 8 µMAX

PART FILTER RESPONSE

OPERATING

VOLTAGE (V)

MAX7418 r = 1.6 +5

MAX7419 Bessel +5

MAX7420 Butterworth +5

MAX7421 r = 1.25 +5

Summary of content (14 pages)

PAGE 1
9-1821; Rev 0; 11/00 5th-Order, Lowpass, Switched-Capacitor Filters Applications ADC Anti-Aliasing CT2 Base Stations DAC Postfiltering Speech Processing Selector Guide PART FILTER RESPONSE OPERATING VOLTAGE (V) MAX7418 r = 1.6 +5 MAX7419 Bessel +5 MAX7420 Butterworth +5 MAX7421 r = 1.
PAGE 2
MAX7418–MAX7425 5th-Order, Lowpass, Switched-Capacitor Filters ABSOLUTE MAXIMUM RATINGS VDD to GND ..............................................................-0.3V to +6V IN, OUT, COM, OS, CLK, SHDN ................-0.3V to (VDD + 0.3V) OUT Short-Circuit Duration.......................................................1s Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW Operating Temperature Ranges MAX74 _ _C_A ..........................................
PAGE 3
5th-Order, Lowpass, Switched-Capacitor Filters (VDD = +5V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND, SHDN = VDD, fCLK = 2.2MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER POWER REQUIREMENTS Supply Voltage Supply Current SYMBOL CONDITIONS MIN TYP MAX UNITS 5.5 V MAX7418/MAX7421 2.9 3.6 MAX7419/MAX7420 3.4 4.1 1 VDD IDD 4.
PAGE 4
MAX7418–MAX7425 5th-Order, Lowpass, Switched-Capacitor Filters ELECTRICAL CHARACTERISTICS—MAX7422–MAX7425 (continued) (VDD = +3V, filter output measured at OUT pin, 10kΩ || 50pF load to GND at OUT, OS = COM, 0.1µF capacitor from COM to GND, SHDN = VDD, fCLK = 2.2MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 5
th-Order, Lowpass, Switched-Capacitor Filters (VDD = +5V for MAX7418–MAX7421, VDD = +3V for MAX7422–MAX7425 filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, SHDN = VDD, fCLK = 2.2MHz, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS BUTTERWORTH FILTERS—MAX7420/MAX7424 Insertion Gain Relative to DC Gain fIN = 0.5fC -0.3 0 fIN = fC -3.6 -3.0 -2.4 fIN = 3fC -47.
PAGE 6
____________________________Typical Operating Characteristics (continued) (VDD = +5V for MAX7418–MAX7421, VDD = +3V for MAX7422–MAX7425, fCLK = 2.2MHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA = +25°C, unless otherwise noted. -10 0.2 0 -0.5 0 GAIN (dB) -30 -40 -50 -1.0 GAIN (dB) -20 -0.2 -0.4 -0.6 -3.0 -70 -0.8 -80 -90 -3.5 -4.0 -1.0 0 20 40 60 80 100 0 4.5 9.0 13.5 18.0 0 22.5 4.5 9.0 13.5 18.0 22.
PAGE 7
5th-Order, Lowpass, Switched-Capacitor Filters MAX7419 THD + NOISE vs. INPUT SIGNAL AMPLITUDE (BESSEL) -20 -40 -50 -20 D -70 -40 -50 -20 0 1 2 4 0 5 -50 D -80 E -90 3 -40 -70 -80 E -90 -30 -60 D -70 -80 E -90 1 2 3 4 5 0 1 2 3 4 5 MAX7421 THD + NOISE vs. INPUT SIGNAL AMPLITUDE (ELLIPTIC, r = 1.25) MAX7422 THD + NOISE vs. INPUT SIGNAL AMPLITUDE (ELLIPTIC, r = 1.6) MAX7423 THD + NOISE vs.
PAGE 8
____________________________Typical Operating Characteristics (continued) (VDD = +5V for MAX7418–MAX7421, VDD = +3V for MAX7422–MAX7425, fCLK = 2.2MHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA = +25°C, unless otherwise noted. ELLIPTIC INTERNAL OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE INTERNAL OSCILLATOR FREQUENCY vs. LARGE CAPACITANCE (nF) 4 BESSEL/BUTTERWORTH 3 2 ELLIPTIC 86.0 85.5 85.0 84.0 0 10 100 COSC = 1000PF 2.5 1000 3.0 3.5 4.0 4.5 5.
PAGE 9
5th-Order, Lowpass, Switched-Capacitor Filters DC OFFSET VOLTAGE vs. SUPPLY VOLTAGE DC OFFSET VOLTAGE vs. TEMPERATURE DC OFFSET VOLTAGE (mV) VDD = 5V 2.0 1.5 1.0 VDD = 3V MAX7418 toc28 2.5 DC OFFSET VOLTAGE (mV) 2.5 MAX7418 toc27 3.0 2.0 1.5 1.0 0.5 0.5 0 0 -40 -15 10 35 60 85 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) TEMPERATURE (°C) Pin Description PIN NAME FUNCTION 1 COM Common Input Pin. Biased internally at midsupply. Bypass COM externally to GND with a 0.
PAGE 10
RS + - VIN L2 C1 L4 C3 C5 RL 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. Butterworth Characteristics Figure 1.
PAGE 11
5th-Order, Lowpass, Switched-Capacitor Filters MAX7418–MAX7425 VSUPPLY 2V/div 0.1µF VDD A 2V/div INPUT IN SHDN OUT COM 0.1µF B 50k MAX7418– MAX7425 2V/div CLOCK C OUTPUT CLK 50k OS 0.1µF GND 200µs/div 50k A: 1kHz INPUT SIGNAL B: MAX7419 BESSEL FILTER RESPONSE; fC = 5kHz C: MAX7420 BUTTERWORTH FILTER RESPONSE; fC = 5kHz Figure 4. Offset Adjustment Circuit Figure 3. Bessel vs.
PAGE 12
MAX7418–MAX7425 5th-Order, Lowpass, Switched-Capacitor Filters 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 supply and the MAX7422–MAX7425 operate from a single +3V supply. Bypass V DD to GND with a 0.1µF capacitor. 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.
PAGE 13
5th-Order, Lowpass, Switched-Capacitor Filters MAX7418–MAX7425 Table 2. MAX7420/MAX7424 Typical Harmonic Distortion FILTER fCLK (MHz) fIN (kHz) 2.2 2 MAX7420 MAX7424 VIN (Vp-p) TYPICAL HARMONIC DISTORTION (dB) 2nd 3rd 4th 5th -77 -67 < -80 -76 < -80 -70 < -80 < -80 < -80 -70 < -80 < -80 < -80 -77 < -80 < -80 4 1.5 2 3.5 3 2.2 2 2 Table 3. MAX7419/MAX7423 Typical Harmonic Distortion FILTER fCLK (MHz) fIN (kHz) 2.
PAGE 14
________________________________________________________Package Information 8LUMAXD.EPS MAX7418–MAX7425 5th-Order, Lowpass, Switched-Capacitor Filters Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.