Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsLinear ICsMAX270EWP+

Digitally-Programmed, Dual

2nd-Order Continuous Lowpass Filter

MAX270/MAX271

19-3701; Rev 2; 1/12

Devices are available in a lead(Pb)-free/RoHS-compliant package.

Specify lead-free by adding a plus (+) to the part number when

ordering.

Ordering Information

Pin Configurations

Typical Operating Circuit

General Description

The MAX270/MAX271 are digitally-programmed, dual

second-order continuous-time lowpass filters. Their typi-

cal dynamic range of 96dB surpasses most switched

capacitor filters which require additional filtering to

remove clock noise. The MAX270/MAX271 are ideal for

anti-aliasing and DAC smoothing applications and can

be cascaded for higher-order responses.

The two filter sections are independently programmable

by either microprocessor (FP) control or pin strapping.

Cutoff frequencies in the 1kHz to 25kHz range can be

selected.

The MAX270 has an on-board, uncommitted op amp,

while the MAX271 has an internal track-and-hold (T/H).

Applications

Lowpass Filtering

Anti-Aliasing Filter

Output Smoothing

Low-Noise Applications

Anti-Aliasing and Track-and-Hold (MAX271)

Features

S Continuous-Time Filtering - No Clock Required

Dual 2nd-Order Lowpass Filters

Sections Independently Programmable: 1kHz to

25kHz

96dB Dynamic Range

No External Components

Cascadable for Higher Order

Low-Power Shutdown Mode

Track-and-Hold (MAX271)

V+

+5V -5V

FILTER A

ANTI-ALIASING

INA OUTAIN

V-GND

FILTER B

ANTI-ALIASING

CSD0-D6

µP OR PIN-STRAP CONTROL

OUTB INB

DSB

DAC

A/D WITH

T/H

OUT

MAX270

OUTA

SHDN D4

OP OUT

V+ D6

OP IN

PDIP/SO(W)

TOP VIEW

INB

OUTB D0

INA

V- D2

GND

Pin Configurations

continued at end

of data sheet

WR CS

10 11

MAX270

PART TEMP RANGE PIN-PACKAGE

MAX270CPP

0NC to +70NC

20 PDIP

MAX270CWP

0NC to +70NC

20 Wide SO

MAX270EPP

-40NC to +85NC

20 PDIP

MAX270EWP

-40NC to +85NC

20 Wide SO

MAX271CNG

0NC to +70NC

20 PDIP

MAX271CWG

0NC to +70NC

20 Wide SO

MAX271ENG

-40NC to +85NC

20 PDIP

MAX271EWG

-40NC to +85NC

20 Wide SO

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

Summary of content (16 pages)

PAGE 1
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter General Description The MAX270/MAX271 are digitally-programmed, dual second-order continuous-time lowpass filters. Their typical dynamic range of 96dB surpasses most switched capacitor filters which require additional filtering to remove clock noise. The MAX270/MAX271 are ideal for anti-aliasing and DAC smoothing applications and can be cascaded for higher-order responses.
PAGE 2
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter ABSOLUTE MAXIMUM RATINGS SO (W) (derate 11.7mW/NC above +70NC)................... 941mw Operating Temperature Ranges: MAX27_C_ _........................................................ 0NC to +70NC MAX27_E_ _..................................................... -40NC to +85NC Storage Temperature Range............................. -65NC to +165NC Lead Temperature (soldering, 10s).................................
PAGE 3
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter ELECTRICAL CHARACTERISTICS (continued) (V+ = +5V, V- = -5V; TA = +25NC, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DYNAMIC FILTER CHARACTERISTICS (MAX270) Total Harmonic Distortion THD Signal Noise Plus Distortion SINAD Spurious-Free Dynamic Range SFDR fC code = 44 (2.01kHz typ), VIN = 3.5VP-P at 390.625Hz (Notes 2 and 3) -70 73 dB 70 UNCOMMITTED AMPLIFIER (MAX270) Slew Rate 1.
PAGE 4
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter TIMING CHARACTERISTICS (Figure 2) (V+ = +5V, V- = -5V; TA = +25NC, unless otherwise noted.
PAGE 5
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter Typical Operating Characteristics (continued) -20 V+ = +5V V- = -5V fC CODE = 44 (2.01kHz TYP) fTEST = 390.625Hz TA = +25˚C VIN = 3.5VP-P -20 GAIN (dB) -3.5 V+ = +5V V- = -5V fC (FILTER A) = fC (FILTER B) = 0-127 (1-25kHz TYP) FILTERS A AND B CASCADED FIGURE 5 TA = +25˚C -4.5 -5.5 -6.5 -7.5 0.
PAGE 6
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter Detailed Description Figures 1a, 1b, and 1c show the MAX270/MAX271 functional diagrams. Both the MAX270 and MAX271 contain two independent, second-order, Sallen-Key, lowpass filter sections, A and B to provide a frequency vs. gain rolloff of approximately 40dB/decade. These are not switched-capacitor filters, but have a continuous-time design similar to discrete active filters built around op amps.
PAGE 7
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter Pin Description (continued) MAX271 PIN NAME FUNCTION, FP MODE (MODE = GND OR V-) 1 T/H OUT Track-and-Hold Output 2 V+ Positive Supply Voltage 3 OUTA Filler A Signal Output 4 SHDN — 5 INA 6 V- 7 INB 8 MODE Negative Supply Voltage Filter B Signal Input Selects FP mode when connected to GND or V- and pin-strap mode when connected to V+.
PAGE 8
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter D0-D6 13-19 V+ V- GND 2 6 9 3 OUTA EN INA 5 fC LATCH A fC LATCH B 8 OUTB EN INB 7 OP IN 20 1 OP OUT EN LATCH CONTROL MAX270 11 10 CS WR A0 4 12 SHDN Figure 1a.
PAGE 9
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter D0-D6 17-23 V+ V- GND 2 6 10 3 OUTA INA 5 EN 1 T/H OUT EN DIRECT CONTROL INB 7 9 OUTB EN PIN-STRAP MODE MAX270 16 15 14 12 4 11 SHDN* T/H* A/B A0* A1* CS* WR* *PIN HAS NO FUNCTION IN PIN-STRAP MODE. 24 13 8 T/H T/H* EN MODE TO GND OR V- Figure 1c. MAX271 Block Diagram—Pin-Strap Mode Filter Programming Cutoff Frequency fC is the frequency of 3dB attenuation in the filter response.
PAGE 10
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter Table 1. Programmed Cutoff Frequency Codes (typ) PROGRAMMED CODE fC (kHz) PROGRAMMED CODE fC (kHz) PROGRAMMED CODE fC (kHz) PROGRAMMED CODE fC (kHz) 0 1.000 32 1.576 64 3.571 96 6.325 1 1.011 33 1.605 65 3.620 97 6.481 2 1.023 34 1.635 66 3.671 98 6.645 3 1.035 35 1.666 67 3.723 99 6.818 4 1.047 36 1.699 68 3.777 100 7.008 5 1.060 37 1.732 69 3.832 101 7.191 6 1.073 38 1.
PAGE 11
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter MAX270 Control Interlace The A0 pin is a three-level input that selects the memory addresses for updating cutoff frequency data in FP mode: A0 SELECTS Logic Low Filter B Logic High Filter A tWH tWS CS tWR WR Figure 2 shows µP-mode interface timing. tAS tAH tDS tDH ADDRESS (A0, A1) Connecting A0 to the negative supply selects pin-strap mode. Pin-strap mode allows filter programming with no timing requirements.
PAGE 12
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter Digital Threshold Levels All digital inputs are TTL and CMOS compatible, unless otherwise stated. Inputs are CMOS gates with less than 1µA leakage current and 8pF capacitance loading. Typical logic voltage thresholds are a function of the V+ supply voltage as shown below (voltages are referenced to GND). V+ (V) LOGIC THRESHOLD VOLTAGE (V) 8 +2.4 7 +2.3 6 +2.0 5 +1.75 4 +1.5 2.5 +1.
PAGE 13
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter Applications Information single supply, the MAX270 A0 pin must be configure with a voltage divider (Figure 4). Power-Supply Configurations Lowest quiescent current in shutdown mode is achieved when A0 is either at V+ or V-. The MAX270/MAX271 power supplies must be properly bypassed. Best performance is achieved if V+ and V- are bypassed to GND with 4.7µF electrolytic (tantalum is preferred) and 0.
PAGE 14
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter INPUT SIGNAL 5 3 7 19 18 17 16 15 14 13 INA OUTB OUTA SHDN V+ INB D6 D5 MAX270 A0 V- OUPUT fC = 1kHz 80dB/dec. ROLLOFF 8 4 +5V 2 12 -5V 6 D4 D3 CS D2 WR D1 OP IN D0 GND 11 10 20 9 Figure 5. Cascading Filter Sections +5V 0.1µF +5V 4.7kI OP OUT OUTB OC VCC 1Q 8Q 1D 8D 100kI +5V V+ D6 OUTA VOUT VBATT SIGNAL B +5V D5 SHDN MAX270 100kI VCC RESET INA MAX690 GND PFI 0.
PAGE 15
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter Chip Information Pin Configurations (continued) PROCESS: BiCMOS TOP VIEW 1 T/H OUT T/H 24 2 V+ D6 23 3 OUTA D5 22 4 SHDN D4 21 5 INA D3 20 6 V- D2 19 7 INB D1 18 8 MODE D0 17 MAX271 9 OUTB A0 16 10 GND A1 15 11 T/H A/B CS 14 12 WR T/H EN 13 Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages.
PAGE 16
MAX270/MAX271 Digitally-Programmed, Dual 2nd-Order Continuous Lowpass Filter Revision History REVISION NUMBER REVISION DATE 0 4/91 Initial release 1 8/91 Revised Electrical Characteristics 2 1/12 Revised Ordering Information and Absolute Maximum Ratings. DESCRIPTION PAGES CHANGED — 2 1, 2 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied.