PART. MAX7410CUA 0 C to +70 C 8 µmax MAX7410EPA MAX7410CPA MAX7410EUA CLOCK

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1 ; Rev 1; 9/98 5th-Order, Lowpass, General Description The 5th-order, lowpass, switched-capacitor filters (SCFs) operate from a single +5 (MAX749/MAX741) or +3 (MAX7413/ MAX7414) supply. These devices draw only 1.2mA of supply current and allow corner frequencies from 1Hz to 15kHz, making them ideal for low-power post-dac filtering and anti-aliasing applications. They feature a shutdown mode, which reduces the supply current to.2. Two clocking options are available on these devices: self-clocking (through the use of an external capacitor) or external clocking for tighter corner-frequency control. An offset adjust pin allows for adjustment of the DC output level. The MAX749/MAX7413 Bessel filters provide low overshoot and fast settling, while the MAX741/MAX7414 Butterworth filters provide a maximally flat passband response. Their fixed response simplifies the design task to selecting a clock frequency. Applications ADC Anti-Aliasing CT2 Base Stations DAC Postfiltering Speech Processing Air-Bag Electronics Selector Guide PART FILTER RESPONSE OPERATING OLTAGE () MAX749 Bessel +5 MAX741 Butterworth +5 MAX7413 Bessel +3 MAX7414 Butterworth +3 Pin Configuration Features 5th-Order Lowpass Filters Bessel Response (MAX749/MAX7413) Butterworth Response (MAX741/MAX7414) Clock-Tunable Corner Frequency (1Hz to 15kHz) Single-Supply Operation +5 (MAX749/MAX741) +3 (MAX7413/MAX7414) Low Power 1.2mA (operating mode).2 (shutdown mode) Available in 8-Pin µmax/dip Packages Low Output Offset: ±4m SUPPLY Ordering Information PART MAX749CUA TEMP. RANGE C to +7 C PIN-PACKAGE 8 µmax MAX749CPA MAX749EUA MAX749EPA C to +7 C -4 C to +85 C -4 C to +85 C 8 Plastic DIP 8 µmax 8 Plastic DIP MAX741CUA C to +7 C 8 µmax MAX741CPA MAX741EUA MAX741EPA C to +7 C -4 C to +85 C -4 C to +85 C 8 Plastic DIP 8 µmax 8 Plastic DIP Ordering Information continued at end of data sheet. Typical Operating Circuit TOP IEW.1µF DD SHDN COM IN GND DD MAX749 MAX741 MAX7413 MAX CLK SHDN OS OUT INPUT CLOCK IN CLK MAX749 MAX741 MAX7413 MAX7414 GND OUT COM OS OUTPUT.1µF µmax/dip Maxim Integrated Products 1 For free samples & the latest literature: or phone For small orders, phone ext

2 ABSOLUTE MAXIMUM RATINGS DD to GND to +6 IN, OUT, COM, OS, CLK, SHDN to ( DD +.3) OUT Short-Circuit Duration...1sec Continuous Power Dissipation (T A = +7 C) 8-Pin DIP (derate 9.9mW/ C above +7 C)...727mW 8-Pin µmax (derate 4.1mW/ C above +7 C)...33mW 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 MAX749/MAX741 Operating Temperature Ranges MAX74 C_A... C to +7 C MAX74 E_A...-4 C to +85 C Storage Temperature Range C to +16 C Lead Temperature (soldering, 1sec)...+3 C ( DD = +5, filter output measured at OUT, 1kΩ 5pF load to GND at OUT, OS = COM,.1µF capacitor from COM to GND, SHDN = DD, f CLK = 1kHz, T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS FILTER CHARACTERISTICS Corner Frequency Clock-to-Corner Ratio Clock-to-Corner Tempco Output oltage Range Output Offset oltage DC Insertion Gain with Output Offset Removed Total Harmonic Distortion plus Noise Offset oltage Gain COM oltage Range Input oltage Range at OS Input Resistance at COM Clock Feedthrough Resistive Output Load Drive Maximum Capacitive Output Load Drive Input Leakage Current at COM Input Leakage Current at OS CLOCK Internal Oscillator Frequency Clock Output Current (Internal Oscillator Mode) Clock Input High Clock Input Low fc f CLK / f c OFFSET THD+N A OS (Note 1) IN = COM = DD / 2 COM = DD / 2 (Note 2) f IN = 2Hz, IN = 4p-p, measurement bandwidth = 22kHz OS to OUT Input, COM externally driven COM Output, COM unconnected OS Input, OS externally driven COM ±.1 R COM R L C L f OSC I CLK IH IL SHDN = GND, COM = to DD OS = to DD C OSC = 1pF (Note 3) CLK = or 5.1 to 15 1: DD -.25 MAX MAX ±4 ± ±.1 ±1 ±.1 ± ±13.5 ±2.5 khz ppm/ C m / kω mp-p kω pf khz 2

3 ELECTRICAL CHARACTERISTICS MAX749/MAX741 ( DD = +5, filter output measured at OUT, 1kΩ 5pF load to GND at OUT, OS = COM,.1µF capacitor from COM to GND, SHDN = DD, f CLK = 1kHz, T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER POWER REQUIREMENTS SYMBOL SHDN = GND IN = COM (Note 4) ELECTRICAL CHARACTERISTICS MAX7413/MAX7414 CONDITIONS MIN TYP MAX Supply oltage DD Supply Current I DD Operating mode, no load Shutdown Current Power-Supply Rejection Ratio SHUTDOWN SHDN Input High SHDN Input Low I SHDN PSRR SDH SDL ( DD = +3, filter output measured at OUT pin, 1kΩ 5pF load to GND at OUT, OS = COM,.1µF capacitor from COM to GND, SHDN = DD, f CLK = 1kHz, T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) SHDN Input Leakage Current SHDN = to DD ±.2 ±1 PARAMETER SYMBOL CONDITIONS MIN TYP MAX FILTER CHARACTERISTICS Corner Frequency f C (Note 1).1 to 15 Clock-to-Corner Ratio f CLK / f C 1:1 Clock-to-Corner Tempco 1 Output oltage Range.25 DD -.25 Output Offset oltage OFFSET IN = COM = DD / 2 ±4 ±25 DC Insertion Gain with Output Offset Removed Maximum Capacitive Output Load Drive Input Leakage Current at COM Input Leakage Current at OS COM = DD / 2 (Note 2) SHDN = GND, COM = to DD OS = to DD Total Harmonic Distortion f THD+N IN = 2Hz, IN = 2.5p-p, MAX plus Noise measurement bandwidth = 22kHz MAX Offset oltage Gain A OS OS to OUT 1 Input, COM externally driven COM oltage Range COM Output, COM unconnected Input oltage Range at OS OS Input, OS externally driven COM ±.1 Input Resistance at COM R COM Clock Feedthrough 3 Resistance Output Load Drive R L 1 1 C L 5 5 ±.1 ±1 ±.1 ±1 UNITS ma UNITS khz ppm/ C m / kω mp-p kω pf 3

4 ELECTRICAL CHARACTERISTICS MAX7413/MAX7414 (continued) ( DD = +3, filter output measured at OUT pin, 1kΩ 5pF load to GND at OUT, OS = COM,.1µF capacitor from COM to GND, SHDN = DD, f CLK = 1kHz, T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) CLOCK PARAMETER Internal Oscillator Frequency Clock Output Current (Internal Oscillator Mode) Clock Input High Clock Input Low POWER REQUIREMENTS Supply oltage Supply Current Shutdown Current Power-Supply Rejection Ratio SHUTDOWN SHDN Input High SHDN Input Low SYMBOL f OSC I CLK IH IL DD I SHDN PSRR SDH SDL CONDITIONS C OSC = 1pF (Note 3) CLK = or 3 Operating mode, no load SHDN = GND IN = COM (Note 4) MIN TYP MAX ±13.5 ± SHDN Input Leakage Current SHDN = to DD.2 ±1 FILTER CHARACTERISTICS UNITS ( DD = +5 for MAX749/MAX741, DD = +3 for MAX7413/MAX7414, filter output measured at OUT, 1kΩ 5pF load to GND at OUT, SHDN = DD, f CLK = 1kHz, T A = T MIN to T MAX, unless otherwise noted.) PARAMETER I DD BESSEL FILTERS MAX749/MAX7413 Insertion Gain Relative to DC Gain CONDITIONS MIN TYP MAX f IN =.5f C f IN = f C f IN = 4f C f IN = 7f C BUTTERWORTH FILTERS MAX741/MAX7414 f IN =.5f C Insertion Gain Relative to f IN = f C DC Gain f IN = 3f C f IN = 5f C khz ma UNITS Note 1: The maximum f C is defined as the clock frequency f CLK = 1 x f C at which the peak S / (THD+N) drops to 68 with a sinusoidal input at.2f C. Note 2: DC insertion gain is defined as OUT / IN. Note 3: f OSC (khz) 3 x 1 3 / C OSC (pf). Note 4: PSRR is the change in output voltage from a DD of 4.5 and a DD of

5 GAIN () GAIN () MAX749/MAX7413 FREQUENCY RESPONSE (BESSEL) f C = 1kHz INPUT FREQUENCY (khz) MAX741/MAX7414 PASSBAND FREQUENCY RESPONSE (BUTTERWORTH) k INPUT FREQUENCY (Hz) SUPPLY CURRENT (ma) f C = 1kHz MAX749 toc1 MAX749 toc4 GAIN () PHASE SHIFT (DEGREES) SUPPLY CURRENT vs. SUPPLY OLTAGE MAX741/MAX7414 FREQUENCY RESPONSE (BUTTERWORTH) f C = 1kHz INPUT FREQUENCY (khz) MAX749/MAX7413 PHASE RESPONSE (BESSEL) f C = 1kHz INPUT FREQUENCY (khz) MAX749 toc7 Typical Operating Characteristics ( DD = +5 for MAX749/MAX741, DD = +3 for MAX7413/MAX7414, f CLK = 1kHz, SHDN = DD, COM = OS = DD / 2, T A = +25 C, unless otherwise noted.) MAX749 toc2 MAX749 toc5 GAIN () PHASE SHIFT (DEGREES) MAX749/MAX7413 PASSBAND FREQUENCY RESPONSE (BESSEL) k INPUT FREQUENCY (Hz) MAX741/MAX7414 PHASE RESPONSE (BUTTERWORTH) f C = 1kHz f C = 1kHz INPUT FREQUENCY (khz) Table A. THD+N vs. Input Signal Amplitude Plot Characteristics LABEL f IN (Hz) f C (khz) A 2 1 B 1k 5 f CLK (khz) 1 5 MAX749 toc3 MAX749 toc6 MEASUREMENT BANDWIDTH (khz) SUPPLY OLTAGE () 5

6 Typical Operating Characteristics (continued) ( DD = +5 for MAX749/MAX741, DD = +3 for MAX7413/MAX7414, f CLK = 1kHz, SHDN = DD, COM = OS = DD / 2, T A = +25 C, unless otherwise noted.) THD + NOISE () THD + NOISE () OSCILLATOR PERIOD (ms) MAX749 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE A B SEE TABLE A AMPLITUDE (p-p) MAX7414 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE AMPLITUDE (p-p) B SEE TABLE A INTERNAL OSCILLATOR PERIOD vs. LARGE CAPACITANCE DD = +5 A DD = CAPACITANCE (nf) MAX749 toc8 MAX749 toc11 MAX749 toc14 THD + NOISE () SUPPLY CURENT (ma) OSCILLATOR FREQUENCY (khz) MAX741 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE AMPLITUDE (p-p) B A SEE TABLE A SUPPLY CURRENT vs. TEMPERATURE DD = TEMPERATURE ( C) DD = +5 INTERNAL OSCILLATOR FREQUENCY vs. SUPPLY OLTAGE C OSC = 1pF SUPPLY OLTAGE () MAX749 toc9 MAX749 toc12 MAX749 toc15 THD + NOISE () OSCILLATOR PERIOD (µs) OSCILLATOR FREQUENCY FREQUENCY (khz) MAX7413 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE A B SEE TABLE A AMPLITUDE (p-p) INTERNAL OSCILLATOR PERIOD vs. SMALL CAPACITANCE DD = +5 DD = CAPACITANCE (pf) INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE DD = +5 C OSC = 1pF DD = TEMPERATURE ( C) MAX749 toc1 MAX749 toc13 MAX749 toc16 6

7 PIN NAME 1 COM 2 IN Filter Input 3 GND Ground FUNCTION Common Input Pin. Biased internally at midsupply. Bypass COM externally to GND with a.1µf capacitor. To override internal biasing, drive COM with an external supply. 4 DD Positive Supply Input: +5 for MAX749/MAX741, +3 for MAX7413/MAX OUT Filter Output 6 OS 7 SHDN Shutdown Input. Drive low to enable shutdown mode; drive high or connect to DD for normal operation. 8 CLK Typical Operating Characteristics (continued) ( DD = +5 for MAX749/MAX741, DD = +3 for MAX7413/MAX7414, f CLK = 1kHz, SHDN = DD, COM = OS = DD / 2, T A = +25 C, unless otherwise noted.) OFFSET OLTAGE (m) OUTPUT OFFSET OLTAGE vs. TEMPERATURE DD = +5 DD = TEMPERATURE ( C) MAX749 toc17 Pin Description Offset Adjust Input. To adjust output offset, connect OS to an external supply through a resistive voltagedivider (Figure 3). Connect OS to COM if no offset adjustment is needed. Refer to the Offset and Common- Mode Input Adjustment section. Clock Input. Connect an external capacitor (C OSC ) from CLK to ground: f OSC (khz) = 3 x 1 3 / C OSC (pf). To override the internal oscillator, connect CLK to an external clock: f C = f CLK /1. DC OFFSET OLTAGE (m) OUTPUT OFFSET OLTAGE vs. SUPPLY OLTAGE SUPPLY OLTAGE () MAX749 toc18 Detailed Description The MAX749/MAX7413 Bessel filters provide low overshoot and fast settling responses, and the MAX741/ MAX7414 Butterworth filters provide a maximally flat passband response. All parts operate with a 1:1 clock-to-corner frequency ratio and a 15kHz maximum corner frequency. Bessel Characteristics Lowpass Bessel filters such as the MAX749/MAX7413 delay all frequency components equally, preserving the shape of step inputs (subject to the attenuation of the higher frequencies). Bessel filters settle quickly an important characteristic in applications that use a multiplexer (mux) to select an input signal for an analog-todigital converter (ADC). An anti-aliasing filter placed between the mux and the ADC must settle quickly after a new channel is selected. Butterworth Characteristics Lowpass Butterworth filters such as the MAX741/ MAX7414 provide a maximally flat passband response, making them ideal for instrumentation applications that require minimum deviation from the DC gain throughout the passband. 7

8 A B C 2µs/div 2/div 2/div 2/div A: 1kHz INPUT SIGNAL B: MAX749 BESSEL FILTER RESPONSE; f C = 5kHz C: MAX741 BUTTERWORTH FILTER RESPONSE; f C = 5kHz Figure 1. Bessel vs. Butterworth Filter Response The difference between Bessel and Butterworth filters can be observed when a 1kHz square wave is applied to the filter input (Figure 1, trace A). With the filter cutoff frequencies set at 5kHz, trace B shows the Bessel filter response and trace C shows the Butterworth filter response. Background Information Most switched-capacitor filters (SCFs) are designed with biquadratic sections. Each section implements two filtering poles, and the sections are cascaded to produce higher-order filters. The advantage to this approach is ease of design. However, this type of design is highly sensitive to component variations if any section s Q is high. An alternative approach is to emulate a passive network using switched-capacitor integrators with summing and scaling. Figure 2 shows a basic 5th-order ladder filter structure. A switched-capacitor filter such as the MAX749/ MAX741/MAX7413/MAX7414 emulates a passive ladder filter. 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-zero pair. In other words, a mismatched component in a biquad design will have a concentrated error on its respective poles, while the same mismatch in a ladder filter design results in an error distributed over all poles. + - R S IN Figure 2. 5th-Order Ladder Filter Network C1 L2 C3 Clock Signal External Clock The family of SCFs is designed for use with external clocks that have a 5% ±1% duty cycle. When using an external clock with these devices, drive CLK with a CMOS gate powered from to DD. arying the rate of the external clock adjusts the corner frequency of the filter as follows: f C = f CLK / 1 Internal Clock When using the internal oscillator, connect a capacitor (C OSC ) between CLK and ground. The value of the capacitor determines the oscillator frequency as follows: f OSC (khz) = 3 x 1 3 / C OSC (pf) Minimize the stray capacitance at CLK so that it does not affect the internal oscillator frequency. ary the rate of the internal oscillator to adjust the filter s corner frequency by a 1:1 clock-to-corner frequency ratio. For example, an internal oscillator frequency of 1kHz produces a nominal corner frequency of 1kHz. Input Impedance vs. Clock Frequencies The s input impedance is effectively that of a switched-capacitor resistor (see the following equation), and is inversely proportional to frequency. The input impedance values determined below represent the average input impedance, since the input current is not continuous. As a rule, use a driver with an output impedance less than 1% of the filter s input impedance. Estimate the input impedance of the filter using the following formula: Z IN = 1 / ( f CLK x 2.1pF) For example, an f CLK of 1kHz results in an input impedance of 4.8MΩ. L4 C5 R L 8

9 Low-Power Shutdown Mode These devices feature a shutdown mode that is activated by driving SHDN low. In shutdown mode, the filter s supply current reduces to.2 and its output becomes high impedance. For normal operation, drive SHDN high or connect it to DD. Applications Information Offset and Common-Mode Input Adjustment The COM pin sets the common-mode input voltage and is biased at mid-supply with an internal resistor-divider. If the application does not require offset adjustment, connect OS to COM. For applications requiring offset adjustment, apply an external bias voltage through a resistor-divider network to OS such as shown in Figure 3. For applications that require DC level shifting, adjust OS with respect to COM. (Note: OS should not be left unconnected.) The output voltage is represented by this equation: OUT = ( IN - COM ) + OS with COM = DD / 2 (typical), and where ( IN - COM ) is lowpass filtered by the SCF, and OS is added at the output stage. See the Electrical Characteristics for the voltage range of COM and OS. Changing the voltage on COM or OS significantly from midsupply reduces the filter s dynamic range. Power Supplies The MAX749/MAX741 operate from a single +5 supply and the MAX7413/MAX7414 operate from a single +3 supply. Bypass DD to GND with a.1µf capacitor. If dual supplies are required (±2.5 for MAX749/MAX741, ±1.5 for MAX7413/MAX7414), connect COM to system ground and connect GND to the negative supply. Figure 4 shows an example of dual-supply operation. Single- and dual-supply performance are equivalent. For either single- or dual-supply operation, drive CLK and SHDN from GND (- in dualsupply operation) to DD. For ±5 dual-supply applications, use the MAX291 MAX297. Input Signal Amplitude Range The optimal input signal range is determined by observing the voltage level at which the Total Harmonic Distortion + Noise is minimized for a given corner frequency. The Typical Operating Characteristics show graphs of the devices Total Harmonic Distortion plus Noise Response as the input signal s peak-to-peak amplitude is varied..1µf INPUT CLOCK SUPPLY IN CLK DD MAX749 MAX741 MAX7413 MAX7414 GND Figure 3. Offset Adjustment Circuit + - INPUT CLOCK IN CLK SHDN OUT COM.1µF.1µF OUTPUT Anti-Aliasing and DAC Postfiltering When using these devices for anti-aliasing or DAC postfiltering, synchronize the DAC (or ADC) and the filter clocks. If the clocks are not synchronized, beat frequencies will alias into the desired passband. Harmonic Distortion Harmonic distortion arises from nonlinearities within the filter. These nonlinearities generate harmonics when a pure sine wave is applied to the filter input. Table 1 lists typical harmonic-distortion values for the MAX741/ MAX7414 with a 1kΩ load at T A = +25 C. Table 2 lists typical harmonic-distortion values for the MAX749/ MAX7413 with a 1kΩ load at T A = +25 C. + DD GND *DRIE SHDN TO - FOR LOW-POWER SHUTDOWN MODE. Figure 4. Dual-Supply Operation - OS MAX749 MAX741 MAX7413 MAX7414 SHDN OUT COM OS * OUTPUT.1µF 5k 5k 5k.1µF 9

10 Table 1. MAX741/MAX7414 Typical Harmonic Distortion FILTER MAX741 MAX7414 Table 2. MAX749/MAX7413 Typical Harmonic Distortion FILTER MAX749 MAX7413 f CLK (khz) f CLK (khz) f IN (Hz) 2 2 f IN (Hz) 2 1k 2 Ordering Information (continued) PART TEMP. RANGE PIN-PACKAGE MAX7413CUA C to +7 C 8 µmax MAX7413CPA C to +7 C 8 Plastic DIP MAX7413EUA -4 C to +85 C 8 µmax MAX7413EPA MAX7414CUA MAX7414CPA MAX7414EUA -4 C to +85 C C to +7 C C to +7 C -4 C to +85 C 1k 1k 1k 8 Plastic DIP 8 µmax 8 Plastic DIP 8 µmax MAX7414EPA -4 C to +85 C 8 Plastic DIP IN (p-p) 4 2 IN (p-p) 4 2 TYPICAL HARMONIC DISTORTION () 2nd TYPICAL HARMONIC DISTORTION () 2nd rd rd TRANSISTOR COUNT: th th th th Chip Information 1

11 Package Information 8LUMAXD.EPS 11

12 Package Information (continued) PDIPN.EPS 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. 12 Maxim Integrated Products, 12 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.