Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsLinear ICsMAX7491CEE+

General Description

The MAX7490/MAX7491 consist of two identical low-

power, low-voltage, wide dynamic range, rail-to-rail,

2nd-order switched-capacitor building blocks. Each of

the two filter sections, together with two to four external

resistors, can generate all standard 2nd-order func-

tions: bandpass, lowpass, highpass, and notch (band

reject). Three of these functions are simultaneously

available. Fourth-order filters can be obtained by cas-

cading the two 2nd-order filter sections. Similarly, high-

er order filters can easily be created by cascading

multiple MAX7490/MAX7491s.

Two clocking options are available: self-clocking

(through the use of an external capacitor) or external

clocking for tighter cutoff frequency control. The clock-

to-center frequency ratio is 100:1. Sampling is done at

twice the clock frequency, further separating the cutoff

frequency and Nyquist frequency.

The MAX7490/MAX7491 have an internal rail splitter

that establishes a precise common voltage needed for

single-supply operation. The MAX7490 operates from a

single +5V supply and the MAX7491 operates from a

single +3V supply. Both devices feature a low-power

shutdown mode and come in a 16-pin QSOP package.

________________________Applications

Tunable Active Filters

Multipole Filters

ADC Anti-Aliasing

Post-DAC Filtering

Adaptive Filtering

Phase-Locked Loops (PLLs)

Set-Top Boxes

Features

o Dual 2nd-Order Filter in a 16-Pin QSOP Package

o High Accuracy

Q Accuracy: ±0.2%

Clock-to-Center Frequency Error: ±0.2%

o Rail-to-Rail Input and Output Operation

o Single-Supply Operation: +5V (MAX7490)

or +3V (MAX7491)

o Internal or External Clock

o Highpass, Lowpass, Bandpass, and Notch Filters

o Clock-to-Center Frequency Ratio of 100:1

o Internal Sampling-to-Center Frequency Ratio

of 200:1

o Center Frequency up to 40kHz

o Easily Cascaded for Multipole Filters

o Low-Power Shutdown: < 1µA Supply Current

MAX7490/MAX7491

Dual Universal Switched-Capacitor Filters

________________________________________________________________

Maxim Integrated Products

LPA LPB

BPB

NB/HPB

INVB

COM

EXTCLK

CLK

TOP VIEW

MAX7490

MAX7491

QSOP

BPA

NA/HPA

SHDN

INVA

GND

Pin Configuration

19-1768; Rev 1; 4/09

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

Ordering Information

PART TEMP RANGE

PIN-

PACKAGE

SUPPLY

VOLTAGE

(+V)

MAX7490CEE+ 0°C to +70°C 16 QSOP 5

MAX7490EEE+ -40°C to +85°C 16 QSOP 5

MAX7491CEE+ 0°C to +70°C 16 QSOP 3

MAX7491EEE+ -40°C to +85°C 16 QSOP 3

Typical Application Circuit appears at end of data sheet.

Denotes a lead(Pb)-free/RoHS-compliant package.

Summary of content (18 pages)

PAGE 1
9-1768; Rev 1; 4/09 Dual Universal Switched-Capacitor Filters The MAX7490/MAX7491 consist of two identical lowpower, low-voltage, wide dynamic range, rail-to-rail, 2nd-order switched-capacitor building blocks. Each of the two filter sections, together with two to four external resistors, can generate all standard 2nd-order functions: bandpass, lowpass, highpass, and notch (band reject). Three of these functions are simultaneously available.
PAGE 2
MAX7490/MAX7491 Dual Universal Switched-Capacitor Filters ABSOLUTE MAXIMUM RATINGS VDD to GND ..............................................................-0.3V to +6V EXTCLK, SHDN to GND ...........................................-0.3V to +6V INV_, LP_, BP_, N_/HP_, S_, COM, CLK to GND............................................-0.3V to (VDD + 0.3V) Maximum Current into Any Pin ...........................................50mA Continuous Power Dissipation (TA = +70°C) 16-Pin QSOP (derate 8.
PAGE 3
Dual Universal Switched-Capacitor Filters (VDD = VEXTCLK = +5V; fCLK = 625kHz; 10kΩ || 50pF load to VDD/2 at LP_, BP_, and N_/HP_; VSHDN = VDD; 0.1µF from COM to GND; 50% duty-cycle clock input; COM = VDD/2; TA = TMIN to TMAX. Typical values are at TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP Clock Input Low MAX 0.5 50 ± 5 Clock Duty Cycle UNITS V % SHDN AND EXTCLK Input High VIH Input Low VIL Input Leakage Current VDD - 0.5 V ±0.4 VINPUT = 0 to VDD 0.
PAGE 4
MAX7490/MAX7491 Dual Universal Switched-Capacitor Filters ELECTRICAL CHARACTERISTICS—MAX7491 (VDD = VEXTCLK = +3V; fCLK = 625kHz; 10kΩ || 50pF load to VDD/2 at LP_, BP_, and N_/HP_; VSHDN = VDD; 0.1µF from COM to GND; 50% duty-cycle clock input; COM = VDD/2; TA = TMIN to TMAX. Typical values are at TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS FILTER Center Frequency Range Clock-to-Center Frequency Accuracy fO fCLK/fO Q Accuracy 0.
PAGE 5
Dual Universal Switched-Capacitor Filters (VDD = VEXTCLK = +3V; fCLK = 625kHz; 10kΩ || 50pF load to VDD/2 at LP_, BP_, and N_/HP_; VSHDN = VDD; 0.1µF from COM to GND; 50% duty-cycle clock input; COM = VDD/2; TA = TMIN to TMAX. Typical values are at TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 3.6 V 4.0 mA 1 μA POWER REQUIREMENTS Supply Voltage VDD Power-Supply Current Shutdown Current 2.
PAGE 6
Typical Operating Characteristics (continued) (VDD = +5V for MAX7490, VDD = +3V for MAX7491, fCLK = 625kHz, VSHDN = VEXTCLK = VDD, COM = VDD/2, Mode 1, R3 = R1 = 50kΩ, R2 = 10kΩ, Q = 5, TA = +25°C, unless otherwise noted.) VDD = 3V -0.2 -0.3 -0.4 -0.5 -0.6 0 20 40 60 80 100 -1 -3 -6 -40 -15 10 35 60 100 85 1000 NOISE vs. Q SUPPLY CURRENT vs. TEMPERATURE 3.7 MAX7490-08 MAX7490-07 500 450 3.6 400 1.0 -0.5 300 IDD (mA) NOISE (µVRMS) 0 250 200 150 -1.0 VDD = 3V 3.5 350 0.
PAGE 7
Dual Universal Switched-Capacitor Filters A = MODE 1 B = MODE 3 A = MODE 1 B = MODE 3 -20 -10 MAX7490-14 -10 MAX7490-13 -20 -30 MAX7490 THD + NOISE vs. INPUT VOLTAGE MAX7491 THD + NOISE vs. INPUT VOLTAGE MAX7490-15 MAX7490 THD + NOISE vs. FREQUENCY A = MODE 1 B = MODE 3 -20 -40 B -80 A THD + NOISE (dB) THD + NOISE (dB) -40 -50 -60 B -90 -110 -80 -120 -90 1k 10k -50 -60 A B -80 A -90 0 0.5 1.0 1.5 2.0 2.5 0 3.
PAGE 8
Dual Universal Switched-Capacitor Filters MAX7490/MAX7491 Pin Description NAME PIN FUNCTION FILTER A FILTER B LP_ 1 16 2nd-Order Lowpass Filter Output BP_ 2 15 2nd-Order Bandpass Filter Output N_/HP_ 3 14 2nd-Order Notch/Highpass Filter Output INV_ 4 13 Inverting Input of Filter Summing Op Amp S_ 5 12 Summing Input. The connection of the summing input, along with the other resistor connections, determine the circuit topology (mode) of each 2ndorder section.
PAGE 9
Dual Universal Switched-Capacitor Filters MAX7490/MAX7491 SHDN (6) VDD (8) INVA (4) BPA (2) NA/HPA (3) + R Σ - ∫ LPA (1) ∫ COM (11) NB/HPB (14) SA (5) + R INVB (13) Σ - BPB (15) ∫ LPB (16) ∫ GND (7) CLK (9) SB (12) EXTCLK (10) Figure 1. Block Diagram 2nd-Order Filter Stage The MAX7490/MAX7491 are dual biquad filters. The biquad topology allows the use of standard filter tables and equations to implement simultaneous lowpass, bandpass, and notch or highpass filters.
PAGE 10
MAX7490/MAX7491 Dual Universal Switched-Capacitor Filters Table 1. Filter Operating Modes MODE LP 1 HP BP N LP-N* HP-N* • • • fCLK/fO ratio is the nominal value. Good for bandpass filters with identical sections cascaded, higher order Butterworth filters, high-Q bandpass, low-Q notches. 1B • • • Same as Mode 1 with fCLK/fO ratios greater than the nominal value. 2 • • • Combination of Mode 1 and Mode 3; fCLK/fO ratios always less than the nominal value.
PAGE 11
Dual Universal Switched-Capacitor Filters R6 R3 R3 R2 N S BP LP R5 COM R2 N R1 VIN + S BP LP R1 - ∫ Σ ∫ COM VIN + - ∫ Σ ∫ COM Figure 2. Mode 1, 2nd-Order Filter Providing Notch, Bandpass, and Lowpass Outputs Figure 3. Mode 1B, 2nd-Order Filter Providing Notch, Bandpass, and Lowpass Outputs Mode 1 Figure 2 shows the MAX7490/MAX7491s’ configuration of Mode 1. This mode provides 2nd-order notch, lowpass, and bandpass filter functions.
PAGE 12
MAX7490/MAX7491 Dual Universal Switched-Capacitor Filters Mode 2 Design Equations f fO = CLK 100 fCLK fn = 100 Q= R3 R2 1+ 1+ CC R2 R4 R4 R3 R2 HP/N VIN R2 + R4 R4 ⎞ −R2 ⎛ HOLP = ⎜ ⎟ R1 ⎝ R4 + R2 ⎠ HOBP = S BP - Σ ∫ ∫ COM −R 3 R1 HON1( f → 0Hz) = Figure 4. Mode 2, 2nd-Order Filter Providing a Highpass Notch, Bandpass, and Lowpass Outputs −R2 ⎛ R4 ⎞ ⎜ ⎟ R1 ⎝ R4 + R2 ⎠ HON2 (at f = fCLK / 2) = Mode 2N Design Equations −R2 R1 Mode 2N Figure 5 shows the configuration of Mode 2N.
PAGE 13
Dual Universal Switched-Capacitor Filters R4 R3 R2 HP VIN BP S LP COM R1 + - Σ ∫ ∫ COM R2 R4 f fO = CLK 100 CC Figure 6. Mode 3, 2nd-Order Section Providing Highpass, Bandpass, and Lowpass Outputs R3 R2 R2 R4 −R2 HOHP = R1 −R4 HOLP = R1 −R3 HOBP = R1 Q= Mode 3A Figure 7 shows the configuration of Mode 3A. Similar to Mode 2, this mode adds an external op amp. See Table 3 for op amp selection ideas.
PAGE 14
MAX7490/MAX7491 Dual Universal Switched-Capacitor Filters Table 3. Suggested External Op Amps PART GBW (MHz) SLEW RATE (V/μs) 2 0.7 ISUPPLY/AMP (mA) 0.5 PIN-PACKAGE MAX4281 MAX4322 5 2.0 1.1 5 SOT23 MAX4130 10 4.0 1.15 5 SOT23 MAX4490 10 10.0 2.
PAGE 15
Dual Universal Switched-Capacitor Filters MODE VOSN/HP VOSBP VOSLP 1 VOS1[1 + (R2 / R3) + (R2 / R1)] - (VOS3) (R2 / R3) VOS3 VOSN/HP - VOS2 1b VOS1[1 + (R2 / R3) + (R2 / R1)] - (VOS3) (R2 / R3) VOS3 (VOSN/HP - VOS2)[1 + R5 / R6)] 2 VOS1[1 + (R2 / R3) + (R2 / R1) + (R2 / R4) (VOS3)(R2 / R3)][R4 / R2 + R4] + (VOS2)[R2 / R2 + R4] VOS3 VOSN/HP - VOS2 3 VOS2 VOS3 VOS1[1 + (R4 / R1) + (R4 / R2) + (R4 / R3)] - (VOS2) (R4 / R2) - (VOS3)(R4 / R3) Aliasing V+ VDD * SHDN 0.
PAGE 16
MAX7490/MAX7491 Dual Universal Switched-Capacitor Filters Table 5. Cascading Identical Bandpass Filter Sections TOTAL SECTIONS TOTAL BW TOTAL Q 1 1.000 B 1.00 Q 2 0.644 B 1.55 Q 3 0.510 B 1.96 Q 4 0.435 B 2.30 Q 5 0.386 B 2.60 Q Wideband Noise The wideband noise of the filter is the total RMS value of the device’s noise spectral density and is used to determine the operating SNR. Most of its frequency contents lie within the filter’s passband and cannot be reduced with postfiltering.
PAGE 17
Dual Universal Switched-Capacitor Filters 4TH-ORDER 10kHz BANDPASS FILTER R1B 200k R3A 200k LPA LPB BPA BPB R2A 10k NA/HPA R1 200k 4TH-ORDER 10kHz BANDPASS FILTER FREQUENCY RESPONSE OUT R3B 200k MAX7490 MAX7491 5 0 R2B 10k -5 NB/HPB VIN INVA SA GAIN (dB) -10 INVB SB -15 -20 -25 SHDN -30 COM GND EXTCLK VDD CLK C2 0.1μF -35 -40 8 VDD fCLK = 1MHz 9 10 11 12 FREQUENCY (kHz) C1 0.
PAGE 18
MAX7490/MAX7491 Dual Universal Switched-Capacitor Filters Revision History REVISION NUMBER REVISION DATE 0 7/00 Initial release 1 4/09 Changes to add lead-free packages, style edits DESCRIPTION PAGES CHANGED — 1–10, 16, 17, 18 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.