MAX291EWE+

MAX291/MAX292/ MAX295/MAX296 8th-Order, Lowpass, Switched-Capacitor Filters LE AVAILAB 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 Ordering Information Applications ADC Anti-Aliasing Filter Noise Analysis DAC Post-Filtering 50Hz/60Hz Line-Noise Filtering Functional Diagrams Typical Operating Circuit +5V PART MAX291CPA MAX291CSA MAX291CWE MAX291C/D MAX291EPA MAX291ESA MAX291EWE MAX291MJA TEMP. RANGE 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -55°C to +125°C Ordering Information continued at end of data sheet. * Contact factory for dice specifications. ** Contact factory for availability and processing to MIL-STD-883. Pin Configurations 7 INPUT 8 V+ IN OUT OP OUT 5 1 OUTPUT TOP VIEW 3 CLK 1 MAX29_ CLOCK 8 IN 7 V+ OP OUT 3 6 GND OP IN- 4 5 OUT V- 2 CLK 6 PIN-PACKAGE 8 Plastic DIP 8 SO 16 Wide SO Dice* 8 Plastic DIP 8 SO 16 Wide SO 8 CERDIP** V- OP IN- 4 2 Pin Configurations appear at end of data sheet. -5V at end of data sheet. Functional Diagrams continued UCSP a trademark of Maxim Integrated Products, Inc. PinisConfiguration is 8-pin DIP/SO. MAX29_ DIP/SO 16-pin Wide SO at end of data sheet. For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com. 19-4526; Rev 5; 5/10 MAX291/MAX292/MAX295/MAX296 8th-Order, Lowpass, Switched-Capacitor Filters 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 +70°C) ...727mW 8-Pin SO (derate 5.88mW/°C above +70°C)................471mW 16-Pin Wide SO (derate 9.52mW/°C above +70°C) ....762mW 8-Pin CERDIP (derate 8.00mW/°C above +70°C)........640mW Operating Temperature Ranges MAX29_C_ _ ........................................................0°C to +70°C MAX29_E_ _ .....................................................-40°C to +85°C MAX29_MJA ..................................................-55°C to +125°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) .......................................+240°C 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, 20kΩ 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 CONDITIONS MIN TYP MAX UNITS 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 0.1-25k 0.1-50k 100:1 50:1 10 40 5 60 fIN = 0.50 Fo MAX291 MAX292 Insertion Gain Relative to DC Gain MAX296 2 ppm/°C -0.02 -0.1 -3.2 fIN = 1.00 Fo -2.2 -2.7 fIN = 2.00 Fo -43.0 -48.0 fIN = 3.00 Fo -70.0 -76.0 fIN = 0.25 Fo -0.1 -0.2 -0.3 fIN = 0.50 Fo -0.6 -0.8 -1.0 fIN = 1.00 Fo -2.7 -3.0 -3.3 fIN = 2.00 Fo -11.0 -13.0 -15.0 fIN = 3.00 Fo -30.0 -34.0 fIN = 4.00 Fo -47.0 -51.0 fIN = 6.00 Fo -74.0 -78.0 fIN = 0.50 Fo MAX295 Hz -0.02 -0.1 -3.2 fIN = 1.00 Fo -2.2 -2.7 fIN = 2.00 Fo -43.0 -48.0 fIN = 3.00 Fo -70.0 -76.0 fIN = 0.25 Fo -0.1 -0.2 -0.3 fIN = 0.50 Fo -0.6 -0.8 -1.0 fIN = 1.00 Fo -2.7 -3.0 -3.3 fIN = 2.00 Fo -11.0 -13.0 -15.0 fIN = 3.00 Fo -30.0 -34.0 fIN = 4.00 Fo -47.0 -51.0 fIN = 6.00 Fo -74.0 -78.0 dB Maxim Integrated MAX291/MAX292/MAX295/MAX296 8th-Order, Lowpass, Switched-Capacitor Filters ELECTRICAL CHARACTERISTICS (continued) (V+ = 5V, V- = -5V, filter output measured at OUT pin, 20kΩ 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 CONDITIONS Output DC Swing Output Offset Voltage MIN TYP MAX UNITS ±150 ±400 V mV 0 -0.15 dB ±4 IN = GND DC Insertion Gain Error with Output Offset Removed 0.15 Total Harmonic Distortion plus Noise TA = +25°C, fCLK = 100kHz Clock Feedthrough fCLK = 100kHz -70 dB 6 mVp-p CLOCK Internal Oscillator Frequency COSC = 1000pF Internal Oscillator Current Source/Sink VCLK = 0V or 5V 29 Clock Input High (Note 1) 35 43 kHz ±70 ±120 µA 4.0 Low UNCOMMITTED OP AMP Input Offset Voltage Output DC Swing Input Bias Current V ±10 1.0 V ±50 mV V µA ±5.500 V 11.000 22 12 V ±4 0.05 POWER REQUIREMENTS Supply Voltage Dual Supply ±2.375 Single Supply V- = 0V, GND = V±2 V+ = 5V, V- = -5V, VCLK = 0V to 5V V+ = 2.375V, V- = -2.375V, VCLK = -2V to 2V Supply Current 4.750 15 7 mA Note 1. Guaranteed by design. Typical Operating Characteristics (V+ = 5V, V- = -5V, TA = +25°C, fCLK = 100kHz (MAX291/MAX292) or fCLK = 50kHz (MAX295/MAX296), unless otherwise noted.) 350 300 250 200 150 100 50 1.030 1.020 1.010 1.000 0.990 NORMALIZED OSCILLATOR FREQUENCY 400 1nF EXTERNAL CAPACITOR CLK MAX291/2/5/6-02 OSCILLATOR PERIOD (µs) 450 NORMALIZED OSCILLATOR FREQUENCY MAX291/2/5/6-01 500 NORMALIZED INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE NORMALIZED INTERNAL OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE 1nF EXTERNAL CAPACITOR CLK 1.06 MAX291/2/5/6-03 INTERNAL OSCILLATOR PERIOD vs. CAPACITANCE VALUE 1.03 1.00 0.97 0.94 0 0 2 4 6 8 10 12 CAPACITANCE (nF) Maxim Integrated 14 16 18 2.0 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0 5.5 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (°C) 3 MAX291/MAX292/MAX295/MAX296 8th-Order, Lowpass, Switched-Capacitor Filters Typical Operating Characteristics (continued) (V+ = 5V, V- = -5V, TA = +25°C, fCLK = 100kHz (MAX291/MAX292) or fCLK = 50kHz (MAX295/MAX296), unless otherwise noted.) MAX295 GAIN (dB) GAIN (dB) -0.3 -0.4 -20 -20 -40 -40 -60 Fo = 1kHz 0 GAIN (dB) MAX291 Fo = 1kHz 0 20 MAX291/2/5/6-05 Fo = 1kHz -0.2 20 MAX291/2/5/6-04 0 -0.1 MAX292/MAX296 FREQUENCY RESPONSE MAX291/MAX295 FREQUENCY RESPONSE MAX291/2/5/6-06 MAX291/MAX295 FREQUENCY RESPONSE -60 MAX296 -80 -0.5 -80 -0.6 -100 -100 -0.7 -120 -120 MAX291 MAX292 600 800 1k 1 2 3 4 0 5 2 4 6 8 INPUT FREQUENCY (Hz) INPUT FREQUENCY (Hz) SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX291/MAX295 FREQUENCY RESPONSE MAX292/MAX296 FREQUENCY RESPONSE 0 14 -10 13 GAIN (dB) 12 11 10 Fo = 1kHz 9 8 7 10 0 Fo = 1kHz -2 -20 -4 -30 -6 MAX296 MAX292 GAIN (dB) 100kHz EXTERNAL CLOCK 15 SUPPLY CURRENT I+ OR |I-|(mA) 0 MAX291/2/5/6-09 400 INPUT FREQUENCY (Hz) MAX291/2/5/6-08 16 200 MAX291/2/5/6-07 0 MAX295 MAX291/MAX295 -40 -8 -50 -10 -60 -12 -70 -14 6 3.5 4.0 4.5 5.0 400 800 1.2k 1.6k INPUT FREQUENCY (Hz) SUPPLY CURRENT vs. TEMPERATURE MAX291/MAX295 PHASE RESPONSE 100kHz EXTERNAL CLOCK I+ OR | I- | 14 13 12 Fo = 1kHz -160 -240 -320 MAX291 -400 0 400 800 1.2k 1.6k 2k MAX292/296 PHASE RESPONSE -80 PHASE SHIFT (Degrees) 15 2k INPUT FREQUENCY (Hz) 0 MAX291/2/5/6-10 16 SUPPLY CURRENT (mA) 0 5.5 0 fo = 1kHz -50 -100 MAX291/2/5/6-12 3.0 SUPPLY VOLTAGE, V+ OR |V-| PHASE SHIFT (Degrees) 2.5 MAX291/2/5/6-11 2.0 -150 -200 -250 -300 -480 11 -560 -350 MAX295 10 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (°C) 4 0 400 800 1.2k INPUT FREQUENCY (Hz) 1.6k 2k 0 400 800 1.2k 1.6k 2k INPUT FREQUENCY (Hz) Maxim Integrated MAX291/MAX292/MAX295/MAX296 8th-Order, Lowpass, Switched-Capacitor Filters Typical Operating Characteristics (continued) (V+ = 5V, V- = -5V, RLOAD = 5kΩ, TA = +25°C, unless otherwise noted.) -4 FC = 2kHz -12 -16 -16 -20 -20 -24 -24 FC = 20kHz 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 B: fCLK = 1MHz Fo = 1kHz INPUT FREQ. = 1kHz MEAS. BANDWIDTH = 80kHz -55 -60 A -65 -70 FC = 1kHz -75 -28 -28 A: fCLK = 200kHz Fo = 2kHz INPUT FREQ. = 200Hz MEAS. BANDWIDTH = 30kHz -45 THD + NOISE (dB) -12 -40 -50 -8 FC = 20kHz -8 GAIN (dB) B -80 1.0 1.1 1.2 1.4 1.3 1 1.5 2 4 3 5 6 7 8 INPUT FREQUENCY (F/FC) AMPLITUDE (Vp-p) MAX296 LOW-VOLTAGE PHASE RESPONSE MAX291 LOW-FREQUENCY PHASE RESPONSE MAX292 THD + NOISE vs. INPUT SIGNAL AMPLITUDE PHASE SHIFT (Degrees) -90 -180 -270 FC = 20kHz -360 FC = 2kHz FC = 20kHz -320 -400 -540 -480 -630 -560 FC = 1kHz 1.1 1.2 1.3 1.5 1.4 1 MAX291/2/5/6-19 D -65 -40 4 5 6 C: fCLK = 200kHz Fo = 4kHz INPUT FREQ. = 400Hz MEAS. BANDWIDTH = 30kHz -45 THD + NOISE (dB) THD + NOISE (dB) 3 8 7 AMPLITUDE (Vp-p) -50 -60 -70 D: fCLK = 1MHz Fo = 20kHz INPUT FREQ. = 2kHz MEAS. BANDWIDTH = 80kHz -55 -60 D -65 -70 -75 -75 C -80 1 2 3 4 5 6 7 AMPLITUDE (Vp-p) Maxim Integrated 2 MAX296 THD + NOISE vs. INPUT SIGNAL AMPLITUDE D: fCLK = 1MHz Fo = 20kHz INPUT FREQ. = 2kHz MEAS. BANDWIDTH = 80kHz -55 A INPUT FREQUENCY (F/FC) C: fCLK = 200kHz Fo = 4kHz INPUT FREQ. = 400Hz MEAS. BANDWIDTH = 30kHz -50 B -65 -70 MAX295 THD + NOISE vs. INPUT SIGNAL AMPLITUDE -45 10 -60 -80 INPUT FREQUENCY (F/FC) -40 9 B: fCLK = 1MHz Fo = 1kHz INPUT FREQ. = 1kHz MEAS. BANDWIDTH = 80kHz -55 -75 1.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 A: fCLK = 200kHz Fo = 2kHz INPUT FREQ. = 200Hz MEAS. BANDWIDTH = 30kHz -45 -50 -240 -450 0 -40 -80 -160 10 MAX291/2/5/6-18 0 V+ = +2.5V V- = -2.5V 0 9 MAX291/2/5/6-20 V+ = +2.5V V- = -2.5V MAX291/2/5/6-17 MAX291/2/5/6-16 INPUT FREQUENCY (F/FC) THD + NOISE (dB) GAIN (dB) -4 PHASE SHIFT (Degrees) V+ = +2.5V V- = -2.5V MAX291/2/5/6-14 0 MAX291/2/5/6-13 V+ = +2.5V V- = -2.5V 0 MAX291 THD + NOISE vs. INPUT SIGNAL AMPLITUDE MAX291 LOW-VOLTAGE FREQUENCY RESPONSE MAX291/2/5/6-15 MAX296 LOW-VOLTAGE FREQUENCY RESPONSE C -80 8 9 10 1 2 3 4 5 6 7 8 9 10 AMPLITUDE (Vp-p) 5 MAX291/MAX292/MAX295/MAX296 8th-Order, Lowpass, Switched-Capacitor Filters _____________________Pin Description 16-PIN NAME FUNCTION 1, 2, 7, 8, 9, 10, 15, 16 N.C. No Connect 1 3 CLK Clock Input. Use internal or external clock. 2 4 V- Negative Supply pin. Dual supplies: -2.375V to -5.500V. Single supplies: V- = 0V. 3 5 OP OUT Uncommitted Op-Amp Output 4 6 OP IN- Inverting Input to the uncommitted op amp. The noninverting op amp is internally tied to ground. 5 11 OUT Filter Output 6 12 GND Ground. In single-supply operation, GND must be biased to the mid-supply voltage level. 7 13 V+ Positive Supply pin. Dual supplies: +2.375V to +5.500V. Single supplies: +4.75V to +11.0V. 8 14 IN Filter Input A AMPLITUDE (5V/div) 8-PIN B C TIME (200µs/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 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 Corner Frequency and Filter Attenuation 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. 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. 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 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 Maxim Integrated MAX291/MAX292/MAX295/MAX296 8th-Order, Lowpass, Switched-Capacitor Filters +5V 7 R1 L1 L3 L5 L7 +5V 1 3 0V C2 C4 C6 C8 4 R2 VIN VO +1V TO +4V INPUT SIGNAL RANGE 8 V+ CLK OUT OP OUT GND IN OUTPUT 0.1µF MAX29_ OP IN- 5 10k 6 V- 10k 2 0.1µF 0V 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. Table 1. Input Impedance for Various Clock Frequencies PART C (pF) 10kHz (MΩ) 100kHz (MΩ) 1000kHz (kΩ) MAX291 MAX292 MAX295 MAX296 2.24 3.28 4.47 4.22 44.6 30.5 22.4 23.7 4.46 3.05 2.24 2.37 446 305 224 237 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 (