Instruction Manual

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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 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.

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

OUTV

CLK

SHDNIN

GND

COM

µMAX/PDIP

TOP VIEW

MAX7426

MAX7427

CLK

OUT

GND

INPUT

0.1µF

CLOCK

SHDN

OUTPUT

COM

MAX7426

MAX7427

SUPPLY

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

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 1-800-998-8800.

For small orders, phone 1-800-835-8769.

Summary of content (12 pages)

PAGE 1
9-1710; Rev 0; 4/00 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters 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 Applications Ordering Information ADC Anti-Aliasing CT2 Base Stations PART TEMP.
PAGE 2
MAX7426/MAX7427 5th-Order, Lowpass, Elliptic, 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 8-Pin PDIP (derate 6.90mW/°C above +70°C).............
PAGE 3
5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters (VDD = +5V, filter output measured at OUT, 10kΩ || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1µF from COM to GND, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS SYMBOL MIN TYP MAX UNITS POWER REQUIREMENTS Supply Voltage VDD Supply Current IDD 5.5 V Operating mode, no load 4.5 0.8 1.0 mA 1 Shutdown Current I SHDN SHDN = GND 0.
PAGE 4
MAX7426/MAX7427 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters ELECTRICAL CHARACTERISTICS—MAX7427 (continued) (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, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 13.5 17.5 21.5 kHz ±7.5 ±12.
PAGE 5
th-Order, Lowpass, Elliptic, Switched-Capacitor Filters (VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA = +25°C, unless otherwise noted.) PASSBAND FREQUENCY RESPONSE GAIN (dB) -30 -0.2 -0.4 -40 -0.6 -50 -60 -0.8 -70 -1.0 1 2 3 4 fC = 1kHz r = 1.25 -150 -200 -250 -300 -350 -400 0 5 -100 INPUT FREQUENCY (kHz) 0.2 0.4 0.6 0.8 1.0 0 0.2 INPUT FREQUENCY (kHz) 0.4 0.6 0.8 1.0 1.2 INPUT FREQUENCY (kHz) SUPPLY CURRENT vs.
PAGE 6
Typical Operating Characteristics (continued) (VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA = +25°C, unless otherwise noted.) 0 MAX7426/27-10 0 SEE TABLE 1. -10 -20 THD + NOISE (dB) -20 -30 -40 -50 -60 -70 SEE TABLE 1. -10 -30 -40 -50 -60 -70 B B -80 -80 A -90 0 1 2 A -90 3 4 0 5 0.5 1.0 1.5 2.0 2.5 AMPLITUDE (Vp-p) AMPLITUDE (Vp-p) Table 1.
PAGE 7
5th-Order, Lowpass, Elliptic, Switched-Capacitor (VDD = +5V for MAX7426, VDD = +3V for MAX7427, fCLK = 100kHz, SHDN = VDD, VCOM = VOS = VDD / 2, TA = +25°C, unless otherwise noted.) INTERNAL OSCILLATOR PERIOD vs. LARGE CAPACITANCE (IN nF) INTERNAL OSCILLATOR PERIOD vs.
PAGE 8
5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters MAX7426/MAX7427 Pin Description PIN NAME FUNCTION Common Input Pin. Biased internally at midsupply. Bypass externally to GND with a 0.1µF capacitor. To override internal biasing, drive with an external supply. 1 COM 2 IN 3 GND Ground 4 VDD Positive Supply Input, +5V for MAX7426 or +3V for MAX7427 5 OUT Filter Output 6 OS Offset Adjust Input.
PAGE 9
5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters RIPPLE 0.1µF VDD fC GAIN (dB) f TRANSITION RATIO = S fC INPUT IN SHDN OUT COM OUTPUT 0.1µF fS 50k MAX7426 MAX7427 CLOCK CLK 50k OS 0.1µF GND PASSBAND 50k STOPBAND fC FREQUENCY fS Figure 2. Elliptic Filter Response Figure 3. Offset Adjustment Circuit powered from 0 to VDD.
PAGE 10
MAX7426/MAX7427 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters For either single-supply or dual-supply operation, drive CLK and SHDN from GND (V- in dual-supply operation) to V DD . Use the MAX7427 for ±2.5, and use the MAX7426 for ±1.5V. For ±5V dual-supply applications, refer to the MAX291/MAX292/MAX295/MAX296 and MAX293/MAX294/MAX297 data sheets. V+ VDD INPUT IN SHDN OUT COM * OUTPUT Input Signal Amplitude Range MAX7426 MAX7427 V+ CLOCK V- CLK OS 0.1µF 0.
PAGE 11
5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters 8LUMAXD.
PAGE 12
MAX7426/MAX7427 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters PDIPN.EPS Package Information (continued) 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.