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 maxi- mally 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? 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 continuous- time 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 compo- nents, the max291 series delivers very aggressive per- formance from a tiny area. applications adc anti-aliasing filter noise analysis dac post-filtering 50hz/60hz line-noise filtering features 8th-order lowpass filters: butterworth (max291/max295) bessel (max292/max296) clock-tunable corner-frequency range: 0.1hz to 25khz (max291/max292) 0.1hz to 50khz (max295/max296) no external resistors or capacitors required internal or external clock clock to corner frequency ratio: 100:1 (max291/max292) 50:1 (max295/max296) low noise: -70db thd + noise (typ) operate with a single +5v supply or dual 5v supplies uncommitted op amp for anti-aliasing or clock- noise filtering 8-pin dip and so packages 8th-order, lowpass, switched-capacitor filters ________________________________________________________________ maxim integrated products 1 19-4526; rev 5; 5/10 max291/max292/max295/max296 ordering information pin configurations ordering information continued at end of data sheet. * contact factory for dice specifications. ** contact factory for availability and processing to mil-std-883. part temp. range pin-package max291 cpa max291cwe 0? to +70? 8 plastic dip max291c/d 0? to +70? 0? to +70? 16 wide so dice* max291epa -40? to +85? 8 plastic dip max291ewe max291mja -55? to +125? -40? to +85? 16 wide so 8 cerdip** gnd op out out op in- 1 2 8 7 in v+ v- clk max29_ dip/so top view 3 4 6 5 16-pin wide so at end of data sheet. max291csa 0? to +70? 8 so max291esa -40? to +85? 8 so +5v -5v v+ v- 8 7 1 6 2 4 3 5 clock clk op in- op out out output input in max29_ typical operating circuit pin configuration is 8-pin dip/so. for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com.
max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v+ = 5v, v- = -5v, filter output measured at out pin, 20k ? load resistor to ground at out and op out, f clk = 100khz (max291/max292) or f clk = 50khz (max295/max296), t a = t min to t max , unless otherwise noted.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. supply voltage (v+ to v-).......................................................12v input voltage at any pin.............v- + (-0.3v) v in v+ + (0.3v) continuous power dissipation 8-pin plastic dip (derate 9.09mw/? above +70?) ...727mw 8-pin so (derate 5.88mw/? above +70?)................471mw 16-pin wide so (derate 9.52mw/? above +70?) ....762mw 8-pin cerdip (derate 8.00mw/? above +70?)........640mw operating temperature ranges max29_c_ _ ........................................................0? to +70? max29_e_ _ .....................................................-40? to +85? max29_mja ..................................................-55? to +125? storage temperature range .............................-65? to +160? lead temperature (soldering, 10s) .................................+300? soldering temperature (reflow) .......................................+240? max295/max296 max291/max292 max296 max295 max291/max292 max295/max296 max291 max292 conditions hz 0.1-50k corner-frequency range 0.1-25k -0.02 -0.1 60 clock to corner frequency tempco 5 100:1 50:1 clock to corner frequency ratio 10 40 units min typ max parameter f in = 0.50 f o f in = 1.00 f o -2.2 -2.7 -3.2 max291 f in = 3.00 f o -70.0 -76.0 f in = 2.00 f o -43.0 -48.0 f in = 0.50 f o -0.6 -0.8 -1.0 f in = 2.00 f o -11.0 -13.0 -15.0 f in = 1.00 f o -2.7 -3.0 -3.3 f in = 0.25 f o -0.1 -0.2 -0.3 f in = 3.00 f o -30.0 -34.0 max292 f in = 6.00 f o -74.0 -78.0 f in = 4.00 f o -47.0 -51.0 f in = 1.00 f o -2.2 -2.7 -3.2 max295 f in = 3.00 f o -70.0 -76.0 f in = 2.00 f o -43.0 -48.0 f in = 0.50 f o f in = 0.50 f o -0.6 -0.8 -1.0 f in = 2.00 f o -11.0 -13.0 -15.0 f in = 1.00 f o -2.7 -3.0 -3.3 f in = 0.25 f o -0.1 -0.2 -0.3 f in = 3.00 f o -30.0 -34.0 max296 f in = 6.00 f o -74.0 -78.0 insertion gain relative to dc gain f in = 4.00 f o -47.0 -51.0 -0.02 -0.1 db ppm/? filter characteristics
max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters _______________________________________________________________________________________ 3 electrical characteristics (continued) (v+ = 5v, v- = -5v, filter output measured at out pin, 20k ? load resistor to ground at out and op out, f clk = 100khz (max291/max292) or f clk = 50khz (max295/max296), t a = t min to t max , unless otherwise noted.) in = gnd v+ = 5v, v- = -5v, v clk = 0v to 5v v- = 0v, gnd = v? v clk = 0v or 5v t a = +25?, f clk = 100khz f clk = 100khz c osc = 1000pf conditions ma 15 22 4.750 11.000 single supply v ?.375 ?.500 supply voltage dual supply ? 0.05 input bias current v ? output dc swing mv ?0 50 input offset voltage db 0.15 0 -0.15 dc insertion gain error with output offset removed mv ?50 ?00 v ? output dc swing output offset voltage 1.0 low v 4.0 clock input high (note 1) ? ?0 120 internal oscillator current source/sink db -70 total harmonic distortion plus noise mvp-p 6 clock feedthrough khz 29 35 43 internal oscillator frequency units min typ max parameter v+ = 2.375v, v- = -2.375v, v clk = -2v to 2v 712 supply current clock uncommitted op amp power requirements v v typical operating characteristics (v+ = 5v, v- = -5v, t a = +25?, f clk = 100khz (max291/max292) or f clk = 50khz (max295/max296), unless otherwise noted.) 0.990 1.000 1.020 1.010 1.030 2.0 3.5 4.0 2.5 3.0 4.5 5.0 5.5 normalized internal oscillator frequency vs. supply voltage max291/2/5/6-02 supply voltage (v) normalized oscillator frequency 1nf external capacitor clk 0 100 50 200 150 300 250 350 450 400 500 0 468 2 1012141618 internal oscillator period vs. capacitance value max291/2/5/6-01 capacitance (nf) oscillator period ( s) 0.97 0.94 1.03 1.00 1.06 -60 -20 0 20 -40 40 60 80 100 120 140 normalized internal oscillator frequency vs. temperature max291/2/5/6-03 temperature ( c) normalized oscillator frequency 1nf external capacitor clk note 1. guaranteed by design.
max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters 4 _______________________________________________________________________________________ -0.6 -0.7 -0.5 -0.2 -0.1 -0.3 -0.4 0 0 200 400 600 800 1k max291/max295 frequency response max291/2/5/6-04 input frequency (hz) gain (db) max295 f o = 1khz max291 -100 -120 -80 -20 0 -40 -60 20 012345 max291/max295 frequency response max291/2/5/6-05 input frequency (hz) gain (db) max295 f o = 1khz max291 -100 -120 -80 -20 0 -40 -60 20 0246810 max292/max296 frequency response max291/2/5/6-06 input frequency (hz) gain (db) max296 f o = 1khz max292 6 9 8 7 11 10 15 14 13 12 16 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 supply current vs. supply voltage max291/2/5/6-07 supply voltage, v+ or |v-| supply current i+ or |i-|(ma) 100khz external clock 10 13 12 11 14 15 16 -60 20 0 -40 -20 40 60 80 100 120 140 supply current vs. temperature max291/2/5/6-10 temperature ( c) supply current (ma) 100khz external clock i+ or | i- | -60 -70 -50 -20 -10 -30 -40 0 0 400 800 1.2k 1.6k 2k max291/max295 frequency response max291/2/5/6-08 input frequency (hz) gain (db) f o = 1khz max291/max295 -12 -14 -10 -4 -2 -6 -8 0 0 400 800 1.2k 1.6k 2k max292/max296 frequency response max291/2/5/6-09 input frequency (hz) gain (db) max296 f o = 1khz max292 -480 -560 -400 -160 -80 -240 -320 0 0 400 800 1.2k 1.6k 2k max291/max295 phase response max291/2/5/6-11 input frequency (hz) phase shift (degrees) max295 f o = 1khz max291 0 0 400 1.2k 2k max292/296 phase response -300 -350 -100 -150 -50 input frequency (hz) phase shift (degrees) 800 1.6k -200 -250 f o = 1khz max291/2/5/6-12 typical operating characteristics (continued) (v+ = 5v, v- = -5v, t a = +25?, f clk = 100khz (max291/max292) or f clk = 50khz (max295/max296), unless otherwise noted.)
max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters _______________________________________________________________________________________ 5 0 0 0.2 0.4 0.6 1.2 1.4 2.0 max296 low-voltage frequency response -24 -28 -8 -12 -4 input frequency (f/fc) gain (db) 0.8 1.0 1.6 1.8 -16 -20 v+ = +2.5v v- = -2.5v f c = 20khz f c = 2khz max291/2/5/6-13 0 1.0 1.1 1.3 1.5 max291 low-voltage frequency response -24 -28 -8 -12 -4 input frequency (f/fc) gain (db) 1.2 1.4 -16 -20 v+ = +2.5v v- = -2.5v f c = 20khz f c = 1khz max291/2/5/6-14 -40 12 3 67 10 max291 thd + noise vs. input signal amplitude -75 -80 -55 -60 -50 -45 amplitude (vp-p) thd + noise (db) 4 589 -65 -70 b a a: f clk = 200khz f o = 2khz input freq. = 200hz meas. bandwidth = 30khz b: f clk = 1mhz f o = 1khz input freq. = 1khz meas. bandwidth = 80khz max291/2/5/6-15 0 0 0.2 0.4 0.6 1.2 1.4 2.0 max296 low-voltage phase response -540 -630 -180 -270 -90 input frequency (f/fc) phase shift (degrees) 0.8 1.0 1.6 1.8 -360 -450 v+ = +2.5v v- = -2.5v f c = 20khz f c = 2khz max291/2/5/6-16 -40 12 3 67 10 max295 thd + noise vs. input signal amplitude -75 -80 -55 -60 -50 -45 amplitude (vp-p) thd + noise (db) 4 589 -65 -70 c d c: f clk = 200khz f o = 4khz input freq. = 400hz meas. bandwidth = 30khz d: f clk = 1mhz f o = 20khz input freq. = 2khz meas. bandwidth = 80khz max291/2/5/6-19 0 1.0 1.1 1.3 1.5 max291 low-frequency phase response -480 -560 -160 -240 -80 input frequency (f/fc) phase shift (degrees) 1.2 1.4 -320 -400 v+ = +2.5v v- = -2.5v f c = 20khz f c = 1khz max291/2/5/6-17 -40 12 3 67 10 max292 thd + noise vs. input signal amplitude -75 -80 -55 -60 -50 -45 amplitude (vp-p) thd + noise (db) 4 589 -65 -70 a b a: f clk = 200khz f o = 2khz input freq. = 200hz meas. bandwidth = 30khz b: f clk = 1mhz f o = 1khz input freq. = 1khz meas. bandwidth = 80khz max291/2/5/6-18 -40 12 3 67 10 max296 thd + noise vs. input signal amplitude -75 -80 -55 -60 -50 -45 amplitude (vp-p) thd + noise (db) 4 589 -65 -70 c d c: f clk = 200khz f o = 4khz input freq. = 400hz meas. bandwidth = 30khz d: f clk = 1mhz f o = 20khz input freq. = 2khz meas. bandwidth = 80khz max291/2/5/6-20 typical operating characteristics (continued) (v+ = 5v, v- = -5v, r load = 5k ? , t a = +25?, unless otherwise noted.)
_______________detailed description lowpass butterworth filters such as the max291/ max295 provide maximally flat passband response, making them ideal for instrumentation applications that require mini- mum 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 high- er frequencies. they also settle faster than butterworth fil- ters. 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)?n 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 frequen- cy components by varying times, causing the overshoot and ringing shown in trace c. 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 (f c ). 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? dc gain. the max295/max296 operate with a 50:1 clock to corner fre- quency 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 biqua- dratic sections. each section implements two filtering poles, and the sections can be cascaded to produce high- er-order filters. the advantage to this approach is ease of design. however, this type of design can display poor sen- sitivity if any section? 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? com- ponent 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 max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters 6 _______________________________________________________________________________________ _____________________pin description filter input 14 8 inverting input to the uncommit- ted op amp. the noninverting op amp is internally tied to ground. 6 4 filter output 11 5 ground. in single-supply oper- ation, gnd must be biased to the mid-supply voltage level. 12 6 positive supply pin. dual sup- plies: +2.375v to +5.500v. single supplies: +4.75v to +11.0v. 13 7 uncommitted op-amp output 5 3 negative supply pin. dual supplies: -2.375v to -5.500v. single supplies: v- = 0v. 4 2 8-pin clock input. use internal or external clock. 3 1 no connect 1, 2, 7, 8, 9, 10, 15, 16 function 16-pin in op in- out gnd v+ op out v- clk n.c. name a b amplitude (5v/div) c a: 3khz input signal b: max292 bessel filter response with f o = 10khz c: max291 butterworth filter response with f o = 10khz time (200 s/div) figure 1. bessel vs. butterworth filter responses
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 proportion- al 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? input source resistance should be less than 10% of the filter? input impedance. the input impedance of the filter can be estimated using the following formula: z = 1 / (f clk * c) where: f clk = clock frequency the input impedance for various clock frequencies is given below: clock-signal requirements the max291/max292/max295/max296 maximum rec- ommended 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 exter- nal 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 clock frequency over the clock range 100khz to 1mhz. varying the rate of an external clock will dynamically ad- just 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 (c osc ) from clk to ground determines the oscillator frequency: the stray capacitance at clk should be minimized be- cause it will affect the internal oscillator frequency. ___________application information power supplies the max291/max292/max295/max296 operate from either dual or single power supplies. the dual-supply volt- age range is +2.375v to +5.500v. the ?.5v dual supply is equivalent to single-supply operation (figure 3). minor per- formance degradation could occur due to the external resistor divider network, where the gnd pin is biased to mid-supply. 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 fre- quency. the typical operating characteristics show the max291/max292/max295/max296 thd + noise response as the input signal? 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 2nd- f khz cpf osc osc () () 10 3 5 max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters _______________________________________________________________________________________ 7 c2 r1 l1 l3 l5 l7 v in c4 c6 c8 r2 v o figure 2. 8th-order ladder filter network max29_ clk 1 +1v to +4v input signal range 5 +5v output 0v 6 3 4 +5v 0v 8 out gnd v- v+ 7 2 op out op in- in 0.1 f 10k 10k 0.1 f figure 3. +5v single-supply operation table 1. input impedance for various clock frequencies 1000khz (k?) 446 305 224 237 100khz (m?) 4.46 3.05 2.24 2.37 10khz (m?) 44.6 30.5 22.4 23.7 c (pf) max291 2.24 max292 3.28 part max295 4.47 max296 4.22 pin configuration is 8-pin dip.
max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters 8 _______________________________________________________________________________________ order continuous lowpass filter. this filter is convenient for anti-aliasing applications, or for clock noise attenuation at the switched-capacitor filter? output. figure 4 shows a 2nd-order lowpass butterworth filter built using the uncommitted op amp with a 10khz corner frequency. this filter? 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 frequen- cies will alias into the desired passband. the dac? clock should be generated by dividing down the switched-capacitor filter? clock. 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 1mhz clock frequency, and a 5k ? load. max29_ 4 c1 330pf 3 input c2 1500pf 22k r1 22k r2 22k r3 output op out op in figure 4. uncommitted op amp configured as a 2nd-order butterworth lowpass filter (f o = 10khz) table 2. typical harmonic distortion (db) -96 -92 -82 -83 -96 -97 -88 -89 -71 -93 -71 -72 -89 -86 -82 -78 4th 5th 2nd 3rd filter harmonic max296 max295 max292 max291 _ordering information (continued) * contact factory for dice specifications. ** contact factory for availability and processing to mil-std-883. pin configuration is 8-pin dip/so. 8 cerdip** -55? to +125? max296mja 16 wide so 8 plastic dip dice* 0? to +70? -40? to +85? -40? to +85? max296ewe 16 wide so 0? to +70? max296epa max296c/d max296cwe 8 plastic dip 8 cerdip** 16 wide so -40? to +85? -55? to +125? 0? to +70? max296 cpa max295mja max295ewe 8 plastic dip -40? to +85? max295epa dice* 16 wide so 0? to +70? 0? to +70? max295c/d 8 plastic dip 0? to +70? max295cwe max295 cpa 8 cerdip** -55? to +125? max292mja 16 wide so 8 plastic dip dice* 0? to +70? -40? to +85? -40? to +85? max292ewe 16 wide so 0? to +70? max292epa max292c/d max292cwe pin-package temp. range part 8 plastic dip 0? to +70? max292 cpa 8 so 0? to +70? max292csa 8 so -40? to +85? MAX292ESA 8 so 0? to +70? max295csa 8 so -40? to +85? max295esa 8 so 0? to +70? max296csa 8 so -40? to +85? max296esa
max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters _______________________________________________________________________________________ 9 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 n.c. n.c. in v+ gnd out n.c. n.c. n.c. n.c. clk v- op out op in- n.c. n.c. top view max29_ wide so ____pin configurations (continued) package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . note that a ?? ?? or ??in the package code indicates rohs status only. package draw- ings may show a different suffix character, but the drawing per- tains to the package regardless of rohs status. package type package code document no. 8 cerdip j8-2 21-0045 8 plastic dip p8-2 21-0043 8 so s8-5 21-0041 16 wide so w16-1 21-0042
max291/max292/max295/max296 8th-order, lowpass, switched-capacitor filters maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it 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 2010 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 3 12/97 4 4/09 added max292 to ordering information table and added new package information section 8 5 5/10 changed voltage range in figure 7 7
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