19-1378; Rev 1; 10/98 KIT ATION EVALU E L B AVAILA 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters Features The MAX7408/MAX7411/MAX7412/MAX7415 5th-order, lowpass, elliptic, switched-capacitor filters (SCFs) operate from a single +5V (MAX7408/MAX7411) or +3V (MAX7412/MAX7415) supply. The 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 can be put into a low-power mode, reducing supply current to 0.2A. Two clocking options are available: self-clocking (through the use of an external capacitor) or external clocking for tighter cutoff-frequency control. An offset-adjust pin allows for adjustment of the DC output level. o 5th-Order, Elliptic Lowpass Filters The MAX7408/MAX7412 deliver 53dB of stopband rejection and a sharp rolloff with a transition ratio of 1.6. The MAX7411/MAX7415 achieve a sharper rolloff with a transition ratio of 1.25 while still providing 37dB of stopband rejection. Their fixed response limits the design task to selecting a clock frequency. o Low Output Offset: 4mV Applications ADC Anti-Aliasing CT2 Base Stations Post-DAC Filtering Speech Processing Selector Guide OPERATING VOLTAGE (V) TRANSITION RATIO PART MAX7408 r = 1.6 +5 MAX7411 r = 1.25 +5 MAX7412 r = 1.6 +3 MAX7415 r = 1.25 +3 Typical Operating Circuit o Low Noise and Distortion: -80dB THD + Noise o Clock-Tunable Corner Frequency (1Hz to 15kHz) o Single-Supply Operation +5V (MAX7408/MAX7411) +3V (MAX7412/MAX7415) o Low Power 1.2mA (operating mode) 0.2A (shutdown mode) o Available in 8-Pin MAX/DIP Packages Ordering Information PART TEMP. RANGE MAX7408CPA 0C to +70C 8 Plastic DIP MAX7408CUA MAX7408EPA MAX7408EUA MAX7411CPA 0C to +70C -40C to +85C -40C to +85C 8 MAX 8 Plastic DIP 8 MAX 0C to +70C 8 Plastic DIP MAX7411CUA MAX7411EPA MAX7411EUA MAX7412CPA 0C to +70C -40C to +85C -40C to +85C 8 MAX 8 Plastic DIP 8 MAX 0C to +70C 8 Plastic DIP MAX7412CUA MAX7412EPA MAX7412EUA MAX7415CPA 0C to +70C -40C to +85C -40C to +85C 8 MAX 8 Plastic DIP 8 MAX 0C to +70C 8 Plastic DIP MAX7415CUA MAX7415EPA MAX7415EUA 0C to +70C -40C to +85C -40C to +85C 8 MAX 8 Plastic DIP 8 MAX VSUPPLY Pin Configuration 0.1F VDD INPUT CLOCK PIN-PACKAGE IN OUT CLK MAX7408 MAX7411 MAX7412 MAX7415 GND TOP VIEW SHDN OUTPUT COM 1 IN GND COM OS 0.1F 2 3 VDD 4 MAX7408 MAX7411 MAX7412 MAX7415 8 CLK 7 SHDN 6 OS 5 OUT MAX/DIP ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX7408/MAX7411/MAX7412/MAX7415 General Description MAX7408/MAX7411/MAX7412/MAX7415 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters ABSOLUTE MAXIMUM RATINGS VDD to GND ..............................................................-0.3V to +6V IN, OUT, COM, OS, CLK, SHDN ................-0.3V to (VDD + 0.3V) OUT Short-Circuit Duration...................................................1sec Continuous Power Dissipation (TA = +70C) 8-Pin DIP (derate 6.90mW/C above +70C) ...............552mW 8-Pin MAX (derate 4.1mW/C above +70C) .............330mW Operating Temperature Ranges MAX74_ _C_A .....................................................0C to +70C MAX74_ _E_A ..................................................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+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--MAX7408/MAX7411 (VDD = +5V; filter output measured at OUT, 10k || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1F from COM to GND, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS FILTER Corner-Frequency Range Clock-to-Corner Ratio fC (Note 1) 0.001 to 15 fCLK/fC Clock-to-Corner Tempco 10 Output Voltage Range Output Offset Voltage 0.25 VOFFSET DC Insertion Gain with Output Offset Removed Total Harmonic Distortion plus Noise Offset Voltage Gain COM Voltage Range Input Voltage Range at OS Input Resistance at COM kHz 100:1 VIN = VCOM = VDD / 2 VCOM = VDD / 2 (Note 2) THD+N AOS fIN = 200Hz, VIN = 4Vp-p, measurement bandwidth = 22kHz V 25 mV 0.2 0.4 dB dB 1 V/V Input, COM externally driven VDD - 0.5 2 VDD 2 VDD + 0.5 2 Output, COM internally driven VDD - 0.2 2 VDD 2 VDD + 0.2 2 V Measured with respect to COM RCOM Clock Feedthrough VDD - 0.25 4 -81 OS to OUT VCOM VOS 0 ppm/C 0.1 110 TA = +25C V 180 k 5 mVp-p Resistive Output Load Drive RL 10 1 k Maximum Capacitive Load at OUT CL 50 500 pF Input Leakage Current at COM SHDN = GND, VCOM = 0 to VDD 0.2 10 A Input Leakage Current at OS VOS = 0 to VDD 0.2 10 A 27 34 kHz 12 20 A CLOCK Internal Oscillator Frequency fOSC Clock Output Current (Internal Oscillator Mode) ICLK Clock Input High VIH Clock Input Low VIL 2 COSC = 1000pF (Note 3) 19 4.5 _______________________________________________________________________________________ V 0.5 V 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters (VDD = +5V; filter output measured at OUT, 10k || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1F from COM to GND, fCLK = 100kHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS SYMBOL MIN TYP MAX UNITS 5.5 V POWER REQUIREMENTS Supply Voltage VDD Supply Current IDD 4.5 Operating mode, no load 1.16 1.5 mA Shutdown Current I SHDN SHDN = GND 0.2 1 A Power-Supply Rejection Ratio PSRR Measured at DC 70 dB SHUTDOWN SHDN Input High VSDH SHDN Input Low VSDL SHDN Input Leakage Current 4.5 VSHDN = 0 to VDD V 0.2 0.5 V 10 A ELECTRICAL CHARACTERISTICS--MAX7412/MAX7415 (VDD = +3V, filter output measured at OUT pin, 10k || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1F from COM to GND, fCLK = 100kHz; TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS FILTER CHARACTERISTICS Corner-Frequency Range Clock-to-Corner Ratio fC (Note 1) 0.001 to 15 fCLK/fC Clock-to-Corner Tempco 10 Output Voltage Range Output Offset Voltage 0.25 VOFFSET DC Insertion Gain with Output Offset Removed Total Harmonic Distortion plus Noise THD+N AOS COM Voltage Range VCOM Input Resistance at COM VIN = VCOM = VDD / 2 VCOM = VDD / 2 (Note 2) Offset Voltage Gain Input Voltage Range at OS kHz 100:1 VOS fIN = 200Hz, VIN = 2.5Vp-p, measurement bandwidth = 22kHz OS to OUT VDD - 0.1 2 Measured with respect to COM RCOM Clock Feedthrough 0 ppm/C VDD - 0.25 25 mV 0.2 0.4 dB -79 dB 1 V/V VDD 2 VDD + 0.1 2 0.1 110 TA = +25C V 4 V V 180 k 3 mVp-p Resistance Output Load Drive RL 10 1 k Maximum Capacitive Load at OUT CL 50 500 pF Input Leakage Current at COM Input Leakage Current at OS SHDN = GND, VCOM = 0 to VDD VOS = 0 to VDD 0.2 10 A 0.2 10 A _______________________________________________________________________________________ 3 MAX7408/MAX7411/MAX7412/MAX7415 ELECTRICAL CHARACTERISTICS--MAX7408/MAX7411 (continued) MAX7408/MAX7411/MAX7412/MAX7415 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters ELECTRICAL CHARACTERISTICS--MAX7412/MAX7415 (continued) (VDD = +3V, filter output measured at OUT pin, 10k || 50pF load to GND at OUT, SHDN = VDD, OS = COM, 0.1F from COM to GND, fCLK = 100kHz; TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 19 27 34 kHz 12 20 A CLOCK Internal Oscillator Frequency fOSC COSC = 1000pF (Note 3) Clock Output Current (Internal Oscillator Mode) ICLK VCLK = 0 or 3V Clock Input High VIH Clock Input Low VIL 2.5 V 0.5 V POWER REQUIREMENTS Supply Voltage VDD Supply Current IDD 3.6 V Operating mode, no load 2.7 1.13 1.5 mA 1 Shutdown Current I SHDN SHDN = GND 0.2 Power-Supply Rejection Ratio PSRR Measured at DC 70 A dB SHUTDOWN SHDN Input High VSDH SHDN Input Low VSDL SHDN Input Leakage Current 2.5 V SHDN = 0 to VDD V 0.2 0.5 V 10 A ELLIPTIC FILTER (r = 1.6) CHARACTERISTICS--MAX7408/MAX7412 (VDD = +5V for MAX7408, VDD = +3V for MAX7412; filter output measured at OUT; 10k || 50pF load to GND at OUT; SHDN = VDD; VCOM = VOS = VDD / 2; fCLK = 100kHz; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25C.) (Note 3) PARAMETER Insertion Gain with DC Gain Error Removed (Note 4) 4 MIN TYP MAX fIN = 0.34fC CONDITIONS -0.4 -0.2 0.4 fIN = 0.63fC -0.4 0.2 0.4 fIN = 0.84fC -0.4 -0.2 0.4 fIN = 0.96fC -0.4 0.2 0.4 fIN = fC -0.7 -0.2 0.2 fIN = 1.60fC -53.4 -50 fIN = 1.90fC -53.4 -50 fIN = 4.62fC -53.4 -50 _______________________________________________________________________________________ UNITS dB 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters (VDD = +5V for MAX7411, VDD = +3V for MAX7415; filter output measured at OUT; 10k || 50pF load to GND at OUT; SHDN = VDD, VCOM = VOS = VDD / 2; fCLK = 100kHz; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25C.) (Note 3) PARAMETER CONDITIONS Insertion Gain with DC Gain Error Removed (Note 4) MIN TYP MAX fIN = 0.38fC -0.4 -0.2 0.4 fIN = 0.68fC -0.4 0.2 0.4 fIN = 0.87fC -0.4 -0.2 0.4 fIN = 0.97fC -0.4 0.2 0.4 fIN = fC -0.7 -0.2 0.2 fIN = 1.25fC -38.5 -34 fIN = 1.43fC -37.2 -35 fIN = 3.25fC -37.2 -35 UNITS dB Note 1: The maximum fC is defined as the clock frequency fCLK = 100 * fC at which the peak SINAD drops to 68dB with a sinusoidal input at 0.2fC. Note 2: DC insertion gain is defined as VOUT / VIN. Note 3: fOSC (kHz) 27 * 103 / COSC (COSC in pF). Note 4: The input frequencies, fIN, are selected at the peaks and troughs of the ideal elliptic frequency responses. Typical Operating Characteristics (VDD = +5V for MAX7408/MAX7411, VDD = +3V for MAX7412/MAX7415; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2; TA = +25C; unless otherwise noted.) MAX7408/MAX7412 FREQUENCY RESPONSE 0 -20 0.2 0 -0.2 -40 -60 GAIN (dB) -20 GAIN (dB) GAIN (dB) fC = 1kHz r = 1.25 -40 -60 -0.4 -0.6 -80 -80 -0.8 -100 -100 -1.0 -120 1 2 3 INPUT FREQUENCY (kHz) 4 5 fC = 1kHz r = 1.6 -1.2 -120 0 MAX7408/11-03 fC = 1kHz r = 1.6 MAX7408/11-02 20 MAX7408/11-01 20 0 MAX7408/MAX7412 PASSBAND FREQUENCY RESPONSE MAX7411/MAX7415 FREQUENCY RESPONSE 0 1 2 3 INPUT FREQUENCY (kHz) 4 5 0 204 408 612 816 1.02k INPUT FREQUENCY (Hz) _______________________________________________________________________________________ 5 MAX7408/MAX7411/MAX7412/MAX7415 ELLIPTIC FILTER (r = 1.25) CHARACTERISTICS--MAX7411/MAX7415 Typical Operating Characteristics (continued) (VDD = +5V for MAX7408/MAX7411, VDD = +3V for MAX7412/MAX7415; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2; TA = +25C; unless otherwise noted.) MAX7411/MAX7415 MAX7408/MAX7412 MAX7411/MAX7415 PHASE RESPONSE PHASE RESPONSE PASSBAND FREQUENCY RESPONSE -0.8 -1.0 fC = 1kHz r = 1.25 -200 -250 -300 204 408 612 816 0 1.02k 0.2 0.8 1.0 1.2 1.4 1.14 1.13 1.12 1.11 3.0 3.5 4.0 4.5 5.0 5.5 0.4 0.6 MAX7408/11-08 1.16 1.15 1.14 VDD = +3V 1.13 -40 -50 -60 -70 1.11 -80 A -20 0 20 40 60 80 100 0 1 2 Table A. THD + Noise Test Conditions fCLK (kHz) MEASUREMENT BANDWIDTH (kHz) -50 A 200 1 100 22 -60 B 1k 5 500 80 -40 B -80 A A -90 0 1 2 3 4 5 AMPLITUDE (Vp-p) 6 3 AMPLITUDE (Vp-p) fC (kHz) B B -90 -40 fIN (Hz) -70 MAX7408/11-06 -30 LABEL -30 1.6 -20 1.12 -60 MAX7408/11-10 -20 1.4 SEE TABLE A MAX7411 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE SEE TABLE A 1.2 -10 TEMPERATURE (C) 0 1.0 0 VDD = +5V 1.17 SUPPLY VOLTAGE (V) -10 0.8 SUPPLY CURRENT vs. TEMPERATURE 1.10 2.5 0.2 MAX7408 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE 1.18 1.15 0 1.6 INPUT FREQUENCY (kHz) 1.19 SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) 1.16 0.6 1.20 MAX7408/11-07 1.17 0.4 INPUT FREQUENCY (kHz) INPUT FREQUENCY (Hz) SUPPLY CURRENT vs. SUPPLY VOLTAGE -400 -600 -400 0 -300 -500 -350 -1.4 -200 MAX7408/11-09 -0.6 -150 THD + NOISE (dB) GAIN (dB) -0.4 -100 fC = 1kHz r = 1.25 -100 PHASE SHIFT (DEGREES) -0.2 -1.2 fC = 1kHz r = 1.6 -50 PHASE SHIFT (DEGREES) 0 0 MAX7408/11-05 0 MAX7408/11-04 0.2 THD + NOISE (dB) MAX7408/MAX7411/MAX7412/MAX7415 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters _______________________________________________________________________________________ 4 5 5th-Order, Lowpass, Elliptic, Switched-Capacitor MAX7412 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE THD + NOISE (dB) -20 -30 -40 -50 -60 -70 SEE TABLE A -10 -30 -40 -50 -60 B B -70 B -80 A -80 A 0 0.5 1.0 1.5 A -90 2.0 2.5 3.0 0 0.5 AMPLITUDE (Vp-p) INTERNAL OSCILLATOR PERIOD vs. LARGE CAPACITANCE (in nF) 60 40 8 MAX7408/11-14 VDD = +3V 6 4 20 2 0 0 500 2.5 3.0 27.4 27.3 27.2 27.1 27.0 26.9 26.8 COSC = 1000pF 26.7 26.6 0 1000 1500 2000 2500 3000 3500 50 100 150 200 250 300 350 2.0 2.5 3.0 3.5 4.0 4.5 CAPACITANCE (pF) CAPACITANCE (nF) SUPPLY VOLTAGE INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE DC OFFSET VOLTAGE vs. TEMPERATURE DC OFFSET VOLTAGE vs. SUPPLY VOLTAGE VDD = +3V 27.0 VDD = +5V 26.5 26.0 -1.0 VDD = +3V -1.5 -2.0 -2.5 VDD = +5V -3.0 -10 10 30 50 TEMPERATURE (C) 70 90 110 -1.0 -1.5 -2.0 -2.5 -3.0 -4.0 -3.5 -30 -0.5 -3.5 COSC = 1000pF 25.5 5.5 MAX7408/11-18 -0.5 5.0 0 DC OFFSET VOLTAGE (mV) 27.5 0 MAX7408/11-17 MAX7408/11-16 28.0 -50 2.0 INTERNAL OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE OSCILLATOR FREQUENCY (kHz) VDD = +3V 0 OSCILLATOR FREQUENCY (kHz) 10 OSCILLATOR PERIOD (ms) 80 VDD = +5V DC OFFSET VOLTAGE (mV) OSCILLATOR PERIOD (s) 100 12 MAX7408/11-13 VDD = +5V 1.5 AMPLITUDE (Vp-p) INTERNAL OSCILLATOR PERIOD vs. SMALL CAPACITANCE (in pF) 120 1.0 MAX7408/11-15 -90 MAX7408/11-12 SEE TABLE A -20 THD + NOISE (dB) 0 MAX7408/11-11 0 -10 MAX7415 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT SIGNAL AMPLITUDE -40 -20 0 20 40 60 TEMPERATURE (C) 80 100 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 7 MAX7408/MAX7411/MAX7412/MAX7415 Typical Operating Characteristics (continued) (VDD = +5V for MAX7408/MAX7411, VDD = +3V for MAX7412/MAX7415; fCLK = 100kHz; SHDN = VDD; VCOM = VOS = VDD / 2; TA = +25C; unless otherwise noted.) MAX7408/MAX7411/MAX7412/MAX7415 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters Pin Description PIN NAME FUNCTION 1 COM 2 IN 3 GND Ground 4 VDD Positive Supply Input, +5V for MAX7408/MAX7411 or +3V for MAX7412/MAX7415 5 OUT Filter Output 6 OS Offset Adjust Input. To adjust output offset, bias OS with a resistive voltage-divider between an external supply and ground. Connect OS to COM if no offset adjustment is needed. 7 SHDN Shutdown Input. Drive low to enable shutdown mode; drive high or connect to VDD for normal operation. 8 CLK Common Input Pin. Biased internally at mid-supply. Bypass externally to GND with 0.1F capacitor. To override internal biasing, drive with an external supply. Filter Input Clock Input. Connect an external capacitor (COSC) from CLK to GND to set the internal oscillator frequency. To override the internal oscillator, connect to an external clock. Detailed Description The MAX7408/MAX7411/MAX7412/MAX7415 family of 5th-order, elliptic, lowpass filters provides sharp rolloff with good stopband rejection. All parts operate with a 100:1 clock-to-corner frequency ratio and a 15kHz maximum corner frequency. Most switched-capacitor filters (SCFs) are designed with biquadratic sections. Each section implements two pole-zero pairs, 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 is highly sensitive to component variations if any section's Q is high. The MAX7408/MAX7411/ MAX7412/MAX7415 use an alternative approach, which is to emulate a passive network using switched-capacitor integrators with summing and scaling. The passive network may be synthesized using CAD programs, or may be found in many filter books. Figure 1 shows a basic 5th-order ladder elliptic filter structure. A switched-capacitor filter that emulates a passive ladder filter retains many of the same advantages. The component sensitivity of a passive ladder filter is low when compared to a cascaded biquadratic design, RS + - VIN C1 C2 C4 L2 L4 C3 C5 Figure 1. 5th-Order Ladder Elliptic Filter Network 8 RL because each component affects the entire filter shape rather than a single pole-zero pair. In other words, a mismatched component in a biquadratic design has a concentrated error on its respective poles, while the same mismatch in a ladder filter design spreads its error over all poles. Elliptic Characteristics Lowpass elliptic filters such as the MAX7408/MAX7411/ MAX7412/MAX7415 provide the steepest possible rolloff with frequency of the four most common filter types (Butterworth, Bessel, Chebyshev, and elliptic). The high Q value of the poles near the passband edge combined with the stopband zeros allows for the sharp attenuation characteristic of elliptic filters, making these devices ideal for anti-aliasing and post-DAC filtering in single-supply systems (see the Anti-Aliasing and PostDAC Filtering section). In the frequency domain, the first transmission zero causes the filter's amplitude to drop to a minimum level. Beyond this zero, the response rises as the frequency increases until the next transmission zero. The stopband begins at the stopband frequency, fS. At frequencies above fS, the filter's gain does not exceed the gain at fS. The corner frequency, fC, is defined as the point where the filter output attenuation falls just below the passband ripple. The transition ratio (r) is defined as the ratio of the stopband frequency to the corner frequency: r = fS / fC The MAX7408/MAX7412 have a translation ratio of 1.6 and typically 53dB of stopband rejection. The MAX7411/MAX7415 have a transition ratio of 1.25 (providing a steeper rolloff) and typically 37dB of stopband rejection. _______________________________________________________________________________________ 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters 0.1F fC VDD f TRANSITION RATIO = S fC GAIN (dB) INPUT SHDN OUT IN 0.1F fS CLOCK PASSBAND MAX7408 MAX7411 MAX7412 MAX7415 CLK fS 50k 50k OS 0.1F GND STOPBAND fC OUTPUT COM 50k FREQUENCY Figure 2. Elliptic Filter Response Figure 3. Offset Adjustment Circuit Clock Signal External Clock These SCFs are designed for use with external clocks that have a 40% to 60% duty cycle. When using an external clock, drive the CLK pin with a CMOS gate powered from 0 to VDD. Varying the rate of the external clock adjusts the corner frequency of the filter: f fC = CLK 100 Internal Clock When using the internal oscillator, the capacitance (COSC) on CLK determines the oscillator frequency: k fOSC (kHz) = COSC (pF) Since COSC is in the low picofarads, minimize the stray capacitance at CLK so that it does not affect the internal oscillator frequency. Varying the rate of the internal oscillator adjusts the filter's corner frequency by a 100:1 clock-to-corner frequency ratio. For example, an internal oscillator frequency of 100kHz produces a nominal corner frequency of 1kHz. Input Impedance vs. Clock Frequencies The MAX7408/MAX7411/MAX7412/MAX7415'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 by the equation represent the average input impedance, since the input current is not continuous. As a rule, use a driver with an output resistance less than 10% of the filter's input impedance. Estimate the input impedance of the filter by using the following formula: ZIN = 1 (fCLK x CIN ) where fCLK = clock frequency and CIN = 1pF. Low-Power Shutdown Mode The MAX7408/MAX7411/MAX7412/MAX7415 have a shutdown mode that is activated by driving SHDN low. In shutdown mode, the filter supply current reduces to 0.2A, and the output of the filter becomes high impedance. For normal operation, drive SHDN high or connect to VDD. Applications Information Offset (OS) and Common-Mode (COM) Input Adjustment COM 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 where offset adjustment is required, apply an external bias voltage through a resistor-divider network to OS, as shown in Figure 3. For applications that require DC level shifting, adjust OS with respect to COM. (Note: Do not leave OS unconnected.) The output voltage is represented by these equations: VOUT = (VIN - VCOM ) + VOS VCOM = VDD 2 (typical) where (VIN - VCOM) is lowpass filtered by the SCF and OS is added at the output stage. See the Electrical _______________________________________________________________________________________ 9 MAX7408/MAX7411/MAX7412/MAX7415 VSUPPLY RIPPLE MAX7408/MAX7411/MAX7412/MAX7415 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters Characteristics table for the input voltage range of COM and OS. Changing the voltage on COM or OS significantly from mid-supply reduces the dynamic range. V+ Power Supplies The MAX7408/MAX7411 operate from a single +5V supply and the MAX7412/MAX7415 operate from a single +3V supply. Bypass V DD to GND with a 0.1F capacitor. If dual supplies are required, connect COM to the system ground and GND to the negative supply. Figure 5 shows an example of dual-supply operation. Single-supply and dual-supply performance are equivalent. For either single-supply or dual-supply operation, drive CLK and SHDN from GND (V- in dual supply operation) to V DD . Use the MAX7408/MAX7411 for 2.5, and use the MAX7412/MAX7415 for 1.5V. For 5V dual-supply applications, see the MAX291/ MAX292/MAX295/MAX296 and MAX293/MAX294/ MAX297 data sheets. VDD INPUT V+ V- CLOCK IN CLK SHDN OUT * OUTPUT COM MAX7408 MAX7411 MAX7412 MAX7415 OS 0.1F 0.1F GND V*CONNECT SHDN TO V- FOR LOW-POWER SHUTDOWN MODE. Input Signal Amplitude Range The optimal input signal range is determined by observing the voltage level at which the signal-to-noise plus distortion (SINAD) ratio is maximized for a given corner frequency. The Typical Operating Characteristics show the THD+Noise response as the input signal's peak-topeak amplitude is varied. Anti-Aliasing and Post-DAC Filtering When using the MAX7408/MAX7411/MAX7412/ MAX7415 for anti-aliasing or post-DAC filtering, synchronize the DAC (or ADC) and the filter clocks. If the Figure 5. Dual-Supply Operation clocks are not synchronized, beat frequencies may 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 with a 10k load at TA = +25C. Table 1. Typical Harmonic Distortion FILTER fCLK (kHz) fIN (Hz) 500 1k MAX7408 TYPICAL HARMONIC DISTORTION (dB) 2nd 3rd 4th 5th TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD TBD 4 100 200 500 1k MAX7411 4 100 200 500 1k MAX7412 2 100 200 500 1k MAX7415 2 100 10 VIN (Vp-p) 200 ______________________________________________________________________________________ 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters TRANSISTOR COUNT: 1457 ________________________________________________________Package Information ______________________________________________________________________________________ 11 MAX7408/MAX7411/MAX7412/MAX7415 Chip Information MAX7408/MAX7411/MAX7412/MAX7415 5th-Order, Lowpass, Elliptic, Switched-Capacitor Filters PDIPN.EPS Package Information (continued) 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, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.