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19-4526; Rev 4; 4/09
8th-Order, Lowpass, Switched-Capacitor Filters
General Description
The MAX291/MAX292/MAX295/MAX296 are easy-to-use, 8th-order, lowpass, switched-capacitor filters that can be set up with corner frequencies from 0.1Hz to 25kHz (MAX291/MAX292) or 0.1Hz to 50kHz (MAX295/MAX296). The MAX291/MAX295 Butterworth filters provide maximally flat passband response, and the MAX292/MAX296 Bessel filters provide low overshoot and fast settling. All four filters have fixed responses, so the design task is limited to selecting the clock frequency that controls the filter's corner frequency. An external capacitor is used to generate a clock using the internal oscillator, or an external clock signal can be used. An uncommitted operational amplifier (noninverting input grounded) is provided for building a continuoustime lowpass filter for post-filtering or anti-aliasing. Produced in an 8-pin DIP/SO and a 16-pin wide SO package, and requiring a minimum of external components, the MAX291 series delivers very aggressive performance from a tiny area.
Features
o 8th-Order Lowpass Filters: Butterworth (MAX291/MAX295) Bessel (MAX292/MAX296) o Clock-Tunable Corner-Frequency Range: 0.1Hz to 25kHz (MAX291/MAX292) 0.1Hz to 50kHz (MAX295/MAX296) o No External Resistors or Capacitors Required o Internal or External Clock o Clock to Corner Frequency Ratio: 100:1 (MAX291/MAX292) 50:1 (MAX295/MAX296) o Low Noise: -70dB THD + Noise (Typ) o Operate with a Single +5V Supply or Dual 5V Supplies o Uncommitted Op Amp for Anti-Aliasing or ClockNoise Filtering o 8-Pin DIP and SO Packages
MAX291/MAX292/MAX295/MAX296
Applications
ADC Anti-Aliasing Filter Noise Analysis DAC Post-Filtering 50Hz/60Hz Line-Noise Filtering
PART MAX291CPA MAX291CSA MAX291CWE MAX291C/D MAX291EPA MAX291ESA MAX291EWE MAX291MJA
Ordering Information
TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 8 SO 16 Wide SO Dice* 8 Plastic DIP 8 SO 16 Wide SO 8 CERDIP**
Typical Operating Circuit
+5V
Ordering Information continued on last page. * Contact factory for dice specifications. ** Contact factory for availability and processing to MIL-STD-883.
7 INPUT 8 V+ IN OUT OP OUT 5 3 CLK 1 4 V- 2 OP OUT 3 OP IN- 4 OUTPUT
Pin Configurations
TOP VIEW
8 IN V+ GND OUT
MAX29_
CLOCK 1 CLK 6 V2 OP IN-
MAX29_
7 6 5
-5V
Pin Configuration is 8-pin DIP/SO.
DIP/SO 16-pin Wide SO on last page. 1
________________________________________________________________ Maxim Integrated Products
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.
8th-Order, Lowpass, Switched-Capacitor Filters MAX291/MAX292/MAX295/MAX296
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V+ to V-).......................................................12V Input Voltage at Any Pin.............V- + (-0.3V) VIN V+ + (0.3V) Continuous Power Dissipation 8-Pin Plastic DIP (derate 9.09mW/C above +70C) ...727mW 8-Pin SO (derate 5.88mW/C above +70C)................471mW 16-Pin Wide SO (derate 9.52mW/C above +70C) ....762mW 8-Pin CERDIP (derate 8.00mW/C above +70C)........640mW Operating Temperature Ranges MAX29_C_ _ ........................................................0C to +70C MAX29_E_ _ .....................................................-40C to +85C MAX29_MJA ..................................................-55C to +125C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10s) .................................+300C
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.
ELECTRICAL CHARACTERISTICS
(V+ = 5V, V- = -5V, filter output measured at OUT pin, 20k load resistor to ground at OUT and OP OUT, fCLK = 100kHz (MAX291/MAX292) or fCLK = 50kHz (MAX295/MAX296), TA = TMIN to TMAX, unless otherwise noted.) PARAMETER FILTER CHARACTERISTICS Corner-Frequency Range Clock to Corner Frequency Ratio Clock to Corner Frequency Tempco MAX291/MAX292 MAX295/MAX296 MAX291/MAX292 MAX295/MAX296 MAX291 MAX292 MAX295 MAX296 fIN = 0.50 Fo MAX291 fIN = 1.00 Fo fIN = 2.00 Fo fIN = 3.00 Fo fIN = 0.25 Fo fIN = 0.50 Fo fIN = 1.00 Fo MAX292 fIN = 2.00 Fo fIN = 3.00 Fo fIN = 4.00 Fo Insertion Gain Relative to DC Gain MAX295 fIN = 6.00 Fo fIN = 0.50 Fo fIN = 1.00 Fo fIN = 2.00 Fo fIN = 3.00 Fo fIN = 0.25 Fo fIN = 0.50 Fo fIN = 1.00 Fo MAX296 fIN = 2.00 Fo fIN = 3.00 Fo fIN = 4.00 Fo fIN = 6.00 Fo 2 -2.2 -43.0 -70.0 -0.1 -0.6 -2.7 -11.0 -30.0 -47.0 -74.0 -2.2 -43.0 -70.0 -0.1 -0.6 -2.7 -11.0 -30.0 -47.0 -74.0 0.1-25k 0.1-50k 100:1 50:1 10 40 5 60 -0.02 -2.7 -48.0 -76.0 -0.2 -0.8 -3.0 -13.0 -34.0 -51.0 -78.0 -0.02 -2.7 -48.0 -76.0 -0.2 -0.8 -3.0 -13.0 -34.0 -51.0 -78.0 -0.3 -1.0 -3.3 -15.0 -0.1 -3.2 dB -0.3 -1.0 -3.3 -15.0 -0.1 -3.2 Hz CONDITIONS MIN TYP MAX UNITS
ppm/C
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8th-Order, Lowpass, Switched-Capacitor Filters
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 5V, V- = -5V, filter output measured at OUT pin, 20k load resistor to ground at OUT and OP OUT, fCLK = 100kHz (MAX291/MAX292) or fCLK = 50kHz (MAX295/MAX296), TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Output DC Swing Output Offset Voltage DC Insertion Gain Error with Output Offset Removed Total Harmonic Distortion plus Noise Clock Feedthrough CLOCK Internal Oscillator Frequency Internal Oscillator Current Source/Sink Clock Input High (Note 1) Low UNCOMMITTED OP AMP Input Offset Voltage Output DC Swing Input Bias Current POWER REQUIREMENTS Supply Voltage Dual Supply Single Supply Supply Current V- = 0V, GND = V2 V+ = 5V, V- = -5V, VCLK = 0V to 5V V+ = 2.375V, V- = -2.375V, VCLK = -2V to 2V 2.375 4.750 15 7 5.500 11.000 22 12 V V mA COSC = 1000pF VCLK = 0V or 5V 4.0 1.0 10 4 0.05 50 29 35 70 43 120 kHz A V V mV V A TA = +25C, fCLK = 100kHz fCLK = 100kHz IN = GND 0.15 CONDITIONS MIN 4 150 0 -70 6 400 -0.15 TYP MAX UNITS V mV dB dB mVp-p
MAX291/MAX292/MAX295/MAX296
Note 1. Guaranteed by design.
Typical Operating Characteristics
(V+ = 5V, V- = -5V, TA = +25C, fCLK = 100kHz (MAX291/MAX292) or fCLK = 50kHz (MAX295/MAX296), unless otherwise noted.)
INTERNAL OSCILLATOR PERIOD vs. CAPACITANCE VALUE
MAX291/2/5/6-01
NORMALIZED INTERNAL OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
MAX291/2/5/6-02
NORMALIZED INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE
NORMALIZED OSCILLATOR FREQUENCY 1nF EXTERNAL CAPACITOR CLK 1.06
MAX291/2/5/6-03
500 450 OSCILLATOR PERIOD (s) 400 350 300 250 200 150 100 50 0 0 2 4 6 8 10 12 14 16
NORMALIZED OSCILLATOR FREQUENCY
1nF EXTERNAL CAPACITOR CLK 1.030
1.020
1.03 1.00
1.010
1.000 0.990 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
0.97 0.94 -60 -40 -20 0 20 40 60 80 100 120 140
18
CAPACITANCE (nF)
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
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3
8th-Order, Lowpass, Switched-Capacitor Filters MAX291/MAX292/MAX295/MAX296
Typical Operating Characteristics (continued)
(V+ = 5V, V- = -5V, TA = +25C, fCLK = 100kHz (MAX291/MAX292) or fCLK = 50kHz (MAX295/MAX296), unless otherwise noted.)
MAX291/MAX295 FREQUENCY RESPONSE
MAX291/2/5/6-04
MAX291/MAX295 FREQUENCY RESPONSE
MAX291/2/5/6-05
MAX292/MAX296 FREQUENCY RESPONSE
0 -20 GAIN (dB) -40 -60 -80 -100 MAX292 -120 MAX296 Fo = 1kHz
MAX291/2/5/6-06
0 -0.1 -0.2 GAIN (dB) -0.3 -0.4 -0.5 -0.6 -0.7 0 200 400 600 800 Fo = 1kHz MAX291 MAX295
20 0 -20 GAIN (dB) -40 -60 -80 -100 -120 MAX295 MAX291 Fo = 1kHz
20
1k
0
1
2
3
4
5
0
2
4
6
8
10
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX291/2/5/6-07
MAX291/MAX295 FREQUENCY RESPONSE
MAX291/2/5/6-08
MAX292/MAX296 FREQUENCY RESPONSE
Fo = 1kHz -2 -4 MAX296 MAX292
MAX291/2/5/6-09
16 15 SUPPLY CURRENT I+ OR I- I(mA) 14 13
100kHz EXTERNAL CLOCK
0 -10 -20 GAIN (dB) MAX291/MAX295 -40 -50 -60 -70 Fo = 1kHz
0
11 10 9 8 7 6 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
GAIN (dB) 1.6k 2k
12
-30
-6 -8 -10 -12 -14
0
400
800
1.2k
0
400
800
1.2k
1.6k
2k
SUPPLY VOLTAGE, V+ OR |V-|
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
SUPPLY CURRENT vs. TEMPERATURE
MAX291/2/5/6-10
MAX291/MAX295 PHASE RESPONSE
MAX291/2/5/6-11
MAX292/296 PHASE RESPONSE
Fo = 1kHz -50 PHASE SHIFT (Degrees) -100 -150 -200 -250 -300 fo = 1kHz
MAX291/2/5/6-12
16 15 SUPPLY CURRENT (mA) 14 13 12 11 100kHz EXTERNAL CLOCK I+ OR | I- |
0 -80 PHASE SHIFT (Degrees) -160 -240 -320 -400 -480 -560 MAX295 0 400 800 1.2k 1.6k MAX291
0
-350 0 400 800 1.2k 1.6k 2k
10 -60 -40 -20 0 20 40 60 80 100 120 140 2k TEMPERATURE (C) INPUT FREQUENCY (Hz) INPUT FREQUENCY (Hz)
4
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8th-Order, Lowpass, Switched-Capacitor Filters
Typical Operating Characteristics (continued)
(V+ = 5V, V- = -5V, RLOAD = 5k, TA = +25C, unless otherwise noted.)
MAX296 LOW-VOLTAGE FREQUENCY RESPONSE
MAX291/2/5/6-13
MAX291/MAX292/MAX295/MAX296
MAX291 LOW-VOLTAGE FREQUENCY RESPONSE
MAX291/2/5/6-14
MAX291 THD + NOISE vs. INPUT SIGNAL AMPLITUDE
-45 -50 THD + NOISE (dB) -55 -60 A -65 -70 -75 -80 B 1 2 3 4 5 6 7 8 9 10 A: fCLK = 200kHz Fo = 2kHz INPUT FREQ. = 200Hz MEAS. BANDWIDTH = 30kHz B: fCLK = 1MHz Fo = 1kHz INPUT FREQ. = 1kHz MEAS. BANDWIDTH = 80kHz
MAX291/2/5/6-15
0 -4 -8 GAIN (dB) V+ = +2.5V V- = -2.5V
-40
0 -4 GAIN (dB) -8 -12
V+ = +2.5V V- = -2.5V
FC = 20kHz FC = 2kHz
-12 -16 -20 -24 -28 FC = 1kHz FC = 20kHz
-16 -20 -24 -28 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 INPUT FREQUENCY (F/FC)
1.0
1.1
1.2
1.3
1.4
1.5
INPUT FREQUENCY (F/FC)
AMPLITUDE (Vp-p)
MAX296 LOW-VOLTAGE PHASE RESPONSE
MAX291/2/5/6-16
MAX291 LOW-FREQUENCY PHASE RESPONSE
MAX291/2/5/6-17
MAX292 THD + NOISE vs. INPUT SIGNAL AMPLITUDE
-45 -50 THD + NOISE (dB) -55 -60 -65 -70 -75 -80 A 1 2 3 4 5 6 7 8 9 10 B A: fCLK = 200kHz Fo = 2kHz INPUT FREQ. = 200Hz MEAS. BANDWIDTH = 30kHz B: fCLK = 1MHz Fo = 1kHz INPUT FREQ. = 1kHz MEAS. BANDWIDTH = 80kHz
MAX291/2/5/6-18
-40
0 PHASE SHIFT (Degrees) -90 -180 -270 -360 -450 -540 -630 0
V+ = +2.5V V- = -2.5V
0 PHASE SHIFT (Degrees) -80 -160 -240 -320 -400 -480 -560 FC = 1kHz
V+ = +2.5V V- = -2.5V
FC = 20kHz FC = 2kHz
FC = 20kHz
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 INPUT FREQUENCY (F/FC)
1.0
1.1
1.2
1.3
1.4
1.5
INPUT FREQUENCY (F/FC)
AMPLITUDE (Vp-p)
MAX295 THD + NOISE vs. INPUT SIGNAL AMPLITUDE
MAX291/2/5/6-19
MAX296 THD + NOISE vs. INPUT SIGNAL AMPLITUDE
-45 -50 THD + NOISE (dB) -55 -60 -65 -70 -75 D C: fCLK = 200kHz Fo = 4kHz INPUT FREQ. = 400Hz MEAS. BANDWIDTH = 30kHz D: fCLK = 1MHz Fo = 20kHz INPUT FREQ. = 2kHz MEAS. BANDWIDTH = 80kHz
MAX291/2/5/6-20
-40 -45 -50 THD + NOISE (dB) -55 -60 -65 -70 -75 -80 1
C: fCLK = 200kHz Fo = 4kHz INPUT FREQ. = 400Hz MEAS. BANDWIDTH = 30kHz D: fCLK = 1MHz Fo = 20kHz INPUT FREQ. = 2kHz MEAS. BANDWIDTH = 80kHz
-40
D
C 2 3 4 5 6 7 8 9 10 AMPLITUDE (Vp-p)
-80 1
C 2 3 4 5 6 7 8 9 10
AMPLITUDE (Vp-p)
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5
8th-Order, Lowpass, Switched-Capacitor Filters MAX291/MAX292/MAX295/MAX296
_____________________Pin Description
1, 2, 7, 8, 9, 10, 15, 16 1 2 3 4 5 6 3 4 5 6 11 12
AMPLITUDE (5V/div)
8-PIN
16-PIN
NAME N.C. CLK VOP OUT OP INOUT GND
FUNCTION No Connect Clock Input. Use internal or external clock. Negative Supply pin. Dual supplies: -2.375V to -5.500V. Single supplies: V- = 0V. Uncommitted Op-Amp Output Inverting Input to the uncommitted op amp. The noninverting op amp is internally tied to ground. Filter Output Ground. In single-supply operation, GND must be biased to the mid-supply voltage level. Positive Supply pin. Dual supplies: +2.375V to +5.500V. Single supplies: +4.75V to +11.0V. Filter Input
A B
C
TIME (200s/div) A: 3kHz INPUT SIGNAL B: MAX292 BESSEL FILTER RESPONSE WITH Fo = 10kHz C: MAX291 BUTTERWORTH FILTER RESPONSE WITH Fo = 10kHz
Figure 1. Bessel vs. Butterworth Filter Responses
7 8
13 14
V+ IN
The MAX291/MAX295 give more attenuation outside the passband. The phase and frequency response curves in the Typical Operating Characteristics reveal the differences between the two types of filters. MAX291/MAX292/MAX295/MAX296 phase shift and gain do not vary significantly from part to part. Typical phase shift and gain differences are less than 0.5% at the corner frequency (FC).
_______________Detailed Description
Lowpass Butterworth filters such as the MAX291/ MAX295 provide maximally flat passband response, making them ideal for instrumentation applications that require minimum deviation from the DC gain throughout the passband. Lowpass Bessel filters such as the MAX292/MAX296 delay all frequency components equally, preserving the shape of step inputs, subject to the attenuation of the higher frequencies. They also settle faster than Butterworth filters. Faster settling can be important in applications that use a multiplexer (mux) to select one signal to be sent to 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 by the mux. The difference in the filters' responses can be observed when a 3kHz square wave is applied to the filter input (Figure 1, trace A). With the filter cutoff frequencies set at 10kHz, trace C shows the MAX291/MAX295 Butterworth filter response and trace B shows the MAX292/MAX296 Bessel filter response. Since the MAX292/MAX296 have a linear phase response in the passband, all frequency components are delayed equally, which preserves the square wave. The filters attenuate higher frequencies of the input square wave, giving rise to the rounded edges at the output. The MAX291/MAX295 delay different frequency components by varying times, causing the overshoot and ringing shown in trace C.
6
Corner Frequency and Filter Attenuation
The MAX291/MAX292 operate with a 100:1 clock to corner frequency ratio and a 25kHz maximum corner frequency, where corner frequency is defined as the point where the filter output is 3dB below the filter's DC gain. The MAX295/MAX296 operate with a 50:1 clock to corner frequency ratio with a 50kHz maximum corner frequency. The 8 poles provide 48dB of attenuation per octave.
Background Information
Most switched-capacitor filters are designed with biquadratic sections. Each section implements two filtering poles, and the sections can be cascaded to produce higher-order filters. The advantage to this approach is ease of design. However, this type of design can display poor sensitivity if any section's Q is high. An alternative approach is to emulate a passive network using switched-capacitor integrators with summing and scaling. The passive network can be synthesized using CAD programs, or can be found in many filter books. Figure 2 shows the basic ladder filter structure. A switched-capacitor filter that emulates a passive ladder filter retains many of its advantages. The filter's component sensitivity is low when compared to a cascaded biquad design because each component affects the entire filter shape, not just one pole pair. That is, a mismatched component in a biquad design will have a concentrated
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8th-Order, Lowpass, Switched-Capacitor Filters MAX291/MAX292/MAX295/MAX296
7 R1 L1 L3 L5 L7 +5V 0V C2 VIN C4 C6 C8 R2 VO 4 -1V to +4V INPUT SIGNAL RANGE 8 1 3 CLK OP OUT V+ OUT 5 0.1F GND V2 6 10k 0.1F 0V 10k +5V OUTPUT
MAX29_
OP ININ
Pin Configuration is 8-pin DIP. Figure 2. 8th-Order Ladder Filter Network Figure 3. +5V Single-Supply Operation
error on its respective poles, while the same mismatch in a ladder filter design will spread its error over all poles. The MAX291/MAX292/MAX295/MAX296 input impedance is effectively that of a switched-capacitor resistor (see equation below, and Table 1), and it is inversely proportional to frequency. The input impedance values determined below represent average input impedance, since the input current is not continuous. The input current flows in a series of pulses that charge the input capacitor every time the appropriate switch is closed. A good rule of thumb is that the driver's input source resistance should be less than 10% of the filter's input impedance. The input impedance of the filter can be estimated using the following formula: Z = 1 / (fCLK * C) where: fCLK = Clock Frequency The input impedance for various clock frequencies is given below:
clock frequency over the clock range 100kHz to 1MHz. Varying the rate of an external clock will dynamically adjust the corner frequency of the filter. Ideally, the MAX291/MAX292/MAX295/MAX296 should be clocked symmetrically (50% duty cycle). MAX291/ MAX292/MAX295/MAX296 can be operated with clock asymmetry of up to 60/40% (or 40/60%) if the clock remains HIGH and LOW for at least 200ns. For example, if the part has a maximum clock rate of 2.5MHz, then the clock should be high for at least 200ns, and low for at least 200ns. When using the internal oscillator, the capacitance (COSC) on the CLK pin determines the oscillator frequency: 10 5 fOSC (kHz) 3COSC (pF) The stray capacitance at CLK should be minimized because it will affect the internal oscillator frequency.
Table 1. Input Impedance for Various Clock Frequencies
PART MAX291 MAX292 MAX295 MAX296 C (pF) 2.24 3.28 4.47 4.22 10kHz (M) 44.6 30.5 22.4 23.7 100kHz (M) 4.46 3.05 2.24 2.37 1000kHz (k) 446 305 224 237
___________Application Information
Power Supplies
The MAX291/MAX292/MAX295/MAX296 operate from either dual or single power supplies. The dual-supply voltage range is +2.375V to +5.500V. The 2.5V dual supply is equivalent to single-supply operation (Figure 3). Minor performance degradation could occur due to the external resistor divider network, where the GND pin is biased to mid-supply.
Clock-Signal Requirements
The MAX291/MAX292/MAX295/MAX296 maximum recommended clock frequency is 2.5MHz, producing a cutoff frequency of 25kHz for the MAX291/MAX292 and 50kHz for the MAX295/MAX296. The CLK pin can be driven by an external clock or by the internal oscillator with an external capacitor. For external clock applications, the clock circuitry has been designed to interface with +5V CMOS logic. Drive the CLK pin with a CMOS gate powered from 0V and +5V when using either a single +5V supply or dual +5V supplies. The MAX291/MAX292/MAX295/MAX296 supply current increases slightly (<3%) with increasing
Input Signal Range
The ideal input signal range is determined by observing at what voltage level the total harmonic distortion plus noise (THD + Noise) ratio is maximized for a given corner frequency. The Typical Operating Characteristics show the MAX291/MAX292/MAX295/MAX296 THD + Noise response as the input signal's peak-to-peak amplitude is varied.
Uncommitted Op Amp
The uncommitted op amp has its noninverting input tied to the GND pin, and can be used to build a 1st- or 2nd7
_______________________________________________________________________________________
8th-Order, Lowpass, Switched-Capacitor Filters MAX291/MAX292/MAX295/MAX296
22k R2 22k R1 INPUT C2 1500pF 22k R3 330pF 4 OP IN 3 OP OUT OUTPUT C1
_Ordering Information (continued)
PART MAX292CPA MAX292CSA MAX292CWE MAX292C/D MAX292EPA MAX292ESA MAX292EWE MAX292MJA MAX295CPA MAX295CSA MAX295CWE MAX295C/D MAX295EPA MAX295ESA MAX295EWE MAX295MJA MAX296CPA MAX296CSA MAX296CWE MAX296C/D MAX296EPA MAX296ESA MAX296EWE MAX296MJA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +85C -55C to +125C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +85C -55C to +125C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 8 SO 16 Wide SO Dice* 8 Plastic DIP 8 SO 16 Wide SO 8 CERDIP** 8 Plastic DIP 8 SO 16 Wide SO Dice* 8 Plastic DIP 8 SO 16 Wide SO 8 CERDIP** 8 Plastic DIP 8 SO 16 Wide SO Dice* 8 Plastic DIP 8 SO 16 Wide SO 8 CERDIP**
MAX29_
Pin Configuration is 8-pin DIP/SO. Figure 4. Uncommitted Op Amp Configured as a 2nd-Order Butterworth Lowpass Filter (Fo = 10kHz)
order continuous lowpass filter. This filter is convenient for anti-aliasing applications, or for clock noise attenuation at the switched-capacitor filter's output. Figure 4 shows a 2nd-order lowpass Butterworth filter built using the uncommitted op amp with a 10kHz corner frequency. This filter's input resistance of 22k satisfies the minimum load requirements of the switched-capacitor filter. The uncommitted op amp (with a 2MHz gain bandwidth product) can alternatively be used at the input of the switched-capacitor filter to help reduce any possible clock ripple feedthrough to the output.
DAC Post-Filtering
When using the MAX291/MAX292/MAX295/MAX296 for DAC post-filtering, synchronize the DAC and the filter clocks. If clocks are not synchronized, beat frequencies will alias into the desired passband. The DAC's clock should be generated by dividing down the switched-capacitor filter's clock.
* Contact factory for dice specifications. ** Contact factory for availability and processing to MIL-STD-883.
Harmonic Distortion
Harmonic distortion arises from nonlinearities within the filters. These nonlinearities generate harmonics when a pure sine wave is applied to the filter input. Table 2 lists typical harmonic distortion values for the MAX291/ MAX292/MAX295/MAX296 with a 1kHz 5Vp-p sine-wave input signal, a 1 MHz clock frequency, and a 5k load.
Table 2. Typical Harmonic Distortion (dB)
Harmonic MAX291 MAX292 MAX295 MAX296 2nd -72 -71 -93 -71 3rd -78 -82 -86 -89 4th -83 -82 -92 -96 5th -89 -88 -97 -96
Filter
8
_______________________________________________________________________________________
8th-Order, Lowpass, Switched-Capacitor Filters
____Pin Configurations (continued)
TOP VIEW
N.C. 1 N.C. 2 CLK 3 V- 4 OP OUT 5 OP IN- 6 N.C. 7 N.C. 8 16 N.C. 15 N.C. 14 IN
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 8 CERDIP 8 Plastic DIP 8 SO 16 Wide SO PACKAGE CODE J8-2 P8-2 S8-5 W16-1 DOCUMENT NO. 21-0045 21-0043 21-0041 21-0042
MAX291/MAX292/MAX295/MAX296
MAX29_
13 V+ 12 GND 11 OUT 10 N.C. 9 N.C.
WIDE SO
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9
8th-Order, Lowpass, Switched-Capacitor Filters MAX291/MAX292/MAX295/MAX296
Revision History
REVISION NUMBER 3 4 REVISION DATE 12/97 4/09 -- Added MAX292 to Ordering Information table and added new Package Information section DESCRIPTION PAGES CHANGED -- 8
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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