LTC1563-2/LTC1563-3 Active RC, 4th Order Lowpass Filter Family U FEATURES DESCRIPTIO ■ The LTC®1563-2/LTC1563-3 are a family of extremely easy-to-use, active RC lowpass filters with rail-to-rail inputs and outputs and low DC offset suitable for systems with a resolution of up to 16 bits. The LTC1563-2, with a single resistor value, gives a unity-gain Butterworth response. The LTC1563-3, with a single resistor value, gives a unity-gain Bessel response. The proprietary architecture of these parts allows for a simple resistor calculation: ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Extremely Easy to Use—A Single Resistor Value Sets the Cutoff Frequency (256Hz < fC < 256kHz) Extremely Flexible—Different Resistor Values Allow Arbitrary Transfer Functions with or without Gain (256Hz < fC < 256kHz) Supports Cutoff Frequencies Up to 360kHz Using FilterCADTM LTC1563-2: Unity-Gain Butterworth Response Uses a Single Resistor Value, Different Resistor Values Allow Other Responses with or without Gain LTC1563-3: Unity-Gain Bessel Response Uses a Single Resistor Value, Different Resistor Values Allow Other Responses with or without Gain Rail-to-Rail Input and Output Voltages Operates from a Single 3V (2.7V Min) to ±5V Supply Low Noise: 36µVRMS for fC = 25.6kHz, 60µVRMS for fC = 256kHz fC Accuracy < ±2% (Typ) DC Offset < 1mV Cascadable to Form 8th Order Lowpass Filters Available in Narrow SSOP-16 Package U APPLICATIO S ■ ■ ■ ■ Discrete RC Active Filter Replacement Antialiasing Filters Smoothing or Reconstruction Filters Linear Phase Filtering for Data Communication Phase Locked Loops where fC is the desired cutoff frequency. For many applications, this formula is all that is needed to design a filter. By simply utilizing different valued resistors, gain and other responses are achieved. The LTC1563-X features a low power mode, for the lower frequency applications, where the supply current is reduced by an order of magnitude and a near zero power shutdown mode. The LTC1563-Xs are available in the narrow SSOP-16 package (Same footprint as an SO-8 package). , LTC and LT are registered trademarks of Linear Technology Corporation. FilterCAD is trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. U ■ R = 10k (256kHz/fC); fC = Cutoff Frequency TYPICAL APPLICATIO Frequency Response Single 3.3V, 256Hz to 256kHz Butterworth Lowpass Filter 0 3.3V 0.1µF LTC1563-2 3 R 4 5 R VIN 0.1µF 6 7 8 LP SA NC INVA NC LPA AGND V – 16 V+ 15 LPB 14 NC 13 INVB 12 NC 11 SB 10 NC 9 EN ( ) 10k fC = 256kHz R R –10 VOUT R = 10k fC = 256kHz –20 GAIN (dB) 1 2 R 10 R –30 R = 10M fC = 256Hz –40 –50 –60 R –70 –80 100 1563 TA01 1k 100k 10k FREQUENCY (Hz) 1M 1563 TA02 156323fa 1 LTC1563-2/LTC1563-3 W U U W W W (Note 1) U ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION TOP VIEW Total Supply Voltage (V + to V –) ............................... 11V Maximum Input Voltage at Any Pin ....................... (V – – 0.3V) ≤ VPIN ≤ (V + + 0.3V) Power Dissipation .............................................. 500mW Operating Temperature Range LTC1563C ............................................... 0°C to 70°C LTC1563I ............................................ – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C LP 1 16 V + SA 2 15 LPB NC 3 14 NC INVA 4 ORDER PART NUMBER LTC1563-2CGN LTC1563-3CGN LTC1563-2IGN LTC1563-3IGN 13 INVB NC 5 12 NC LPA 6 11 SB AGND 7 10 NC V– 8 9 GN PART MARKING EN GN PACKAGE 16-LEAD PLASTIC SSOP 15632 15633 15632I 15633I TJMAX = 150°C, θJA = 135°C/ W NOTE: PINS LABELED NC ARE NOT CONNECTED INTERNALLY AND SHOULD BE CONNECTED TO THE SYSTEM GROUND Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for Military grade parts. ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VS = Single 4.75V, EN pin to logic “low,” Gain = 1, RFIL = R11 = R21 = R31 = R12 = R22 = R32, specifications apply to both the high speed (HS) and low power (LP) modes unless otherwise noted. PARAMETER CONDITIONS Specifications for Both LTC1563-2 and LTC1563-3 MIN TYP MAX UNITS Total Supply Voltage (VS), HS Mode ● 3 11 V Total Supply Voltage (VS), LP Mode ● 2.7 11 V 2.9 4.55 4.8 Output Voltage Swing High (LPB Pin) HS Mode VS = 3V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND VS = 4.75V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND VS = ±5V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND ● ● ● Output Voltage Swing Low (LPB Pin) HS Mode VS = 3V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND VS = 4.75V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND VS = ±5V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND ● ● ● Output Swing High (LPB Pin) LP Mode VS = 2.7V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND VS = 4.75V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND VS = ±5V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND ● ● ● Output Swing Low (LPB Pin) LP Mode VS = 2.7V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND VS = 4.75V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND VS = ±5V, fC = 25.6kHz, RFIL = 100k, RL = 10k to GND ● ● ● 0.01 0.015 – 4.95 0.05 0.05 – 4.9 DC Offset Voltage, HS Mode (Section A Only) VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● ±1.5 ±1.0 ±1.5 ±3 ±3 ±3 mV mV mV DC Offset Voltage, LP Mode (Section A Only) VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● ±2 ±2 ±2 ±6 ±6 ±7 mV mV mV DC Offset Voltage, HS Mode (Input to Output, Sections A, B Cascaded) VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● ±1.5 ±1.0 ±1.5 ±3 ±3 ±3 mV mV mV 2.95 4.7 4.9 0.015 0.02 – 4.95 2.6 4.55 4.8 V V V 0.05 0.05 – 4.9 2.65 4.65 4.9 V V V V V V V V V 156323fa 2 LTC1563-2/LTC1563-3 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VS = Single 4.75V, EN pin to logic “low,” Gain = 1, RFIL = R11 = R21 = R31 = R12 = R22 = R32, specifications apply to both the high speed (HS) and low power (LP) modes unless otherwise noted. PARAMETER DC Offset Voltage, LP Mode (Input to Output, Sections A, B Cascaded) CONDITIONS VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● MIN TYP ±2 ±2 ±2 DC Offset Voltage Drift, HS Mode (Input to Output, Sections A, B Cascaded) VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● 10 10 10 µV/°C µV/°C µV/°C DC Offset Voltage Drift, LP Mode (Input to Output, Sections A, B Cascaded) VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● 10 10 10 µV/°C µV/°C µV/°C AGND Voltage VS = 4.75V, fC = 25.6kHz, RFIL = 100k ● 2.375 2.40 Power Supply Current, HS Mode VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● 8.0 10.5 15 14 17 23 mA mA mA Power Supply Current, LP Mode VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● 1.0 1.4 2.3 1.8 2.5 3.5 mA mA mA Shutdown Mode Supply Current VS = 4.75V, fC = 25.6kHz, RFIL = 100k ● 1 20 µA EN Input Logic Low Level VS = 3V VS = 4.75V VS = ±5V ● ● ● 0.8 1 1 V V V EN Input Logic High Level VS = 3V VS = 4.75V VS = ±5V ● ● ● LP Logic Low Level VS = 3V VS = 4.75V VS = ±5V ● ● ● LP Logic High Level VS = 3V VS = 4.75V VS = ±5V ● ● ● 2.5 4.3 4.4 Cutoff Frequency Range, fC HS Mode (Note 2) VS = 3V VS = 4.75V VS = ±5V ● ● ● 0.256 0.256 0.256 256 256 256 kHz kHz kHz Cutoff Frequency Range, fC LP Mode (Note 2) VS = 2.7V VS = 4.75V VS = ±5V ● ● ● 0.256 0.256 0.256 25.6 25.6 25.6 kHz kHz kHz Cutoff Frequency Accuracy, HS Mode fC = 25.6kHz VS = 3V, RFIL = 100k VS = 4.75V, RFIL = 100k VS = ±5V, RFIL = 100k ● ● ● –2.0 –2.0 –2.0 ±1.5 ±1.5 ±1.5 3.5 3.5 3.5 % % % Cutoff Frequency Accuracy, HS Mode fC = 256kHz VS = 3V, RFIL = 10k VS = 4.75V, RFIL = 10k VS = ±5V, RFIL = 10k ● ● ● –5 –5 –5 ±1.5 ±1.5 ±1.5 2.5 2.5 2.5 % % % Cutoff Frequency Accuracy, LP Mode fC = 25.6kHz VS = 2.7V, RFIL = 100k VS = 4.75V, RFIL = 100k VS = ±5V, RFIL = 100k ● ● ● –3 –3 –3 ±1.5 ±1.5 ±1.5 3 3 3 % % % Cutoff Frequency Temperature Coefficient (Note 3) ● 2.35 MAX ±7 ±7 ±8 2.5 4.3 4.4 UNITS mV mV mV V V V V 0.8 1 1 V V V V V V LTC1563-2 Transfer Function Characteristics ±1 ppm/°C 156323fa 3 LTC1563-2/LTC1563-3 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VS = Single 4.75V, EN pin to logic “low,” Gain = 1, RFIL = R11 = R21 = R31 = R12 = R22 = R32, specifications apply to both the high speed (HS) and low power (LP) modes unless otherwise noted. PARAMETER Passband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k CONDITIONS Test Frequency = 2.56kHz (0.1 • fC) Test Frequency = 12.8kHz (0.5 • fC) ● ● Stopband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Test Frequency = 51.2kHz (2 • fC) Test Frequency = 102.4kHz (4 • fC) ● ● Passband Gain, HS Mode, fC = 256kHz VS = 4.75V, RFIL = 10k Test Frequency = 25.6kHz (0.1 • fC) Test Frequency = 128kHz (0.5 • fC) ● ● Stopband Gain, HS Mode, fC = 256kHz VS = 4.75V, RFIL = 10k Test Frequency = 400kHz (1.56 • fC) Test Frequency = 500kHz (1.95 • fC) ● ● Passband Gain, LP Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Test Frequency = 2.56kHz (0.1 • fC) Test Frequency = 12.8kHz (0.5 • fC) ● ● Stopband Gain, LP Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Test Frequency = 51.2kHz (2 • fC) Test Frequency = 102.4kHz (4 • fC) ● ● Cutoff Frequency Range, fC HS Mode (Note 2) VS = 3V VS = 4.75V VS = ±5V ● ● ● Cutoff Frequency Range, fC LP Mode (Note 2) VS = 2.7V VS = 4.75V VS = ±5V Cutoff Frequency Accuracy, HS Mode fC = 25.6kHz MIN – 0.2 – 0.3 TYP 0 0 MAX 0.2 0.3 UNITS dB dB – 24 – 48 – 21.5 – 46 dB dB 0 0 0.2 0.5 dB dB – 15.7 – 23.3 –13.5 – 21.5 dB dB 0 – 0.02 0.25 0.6 dB dB – 24 – 48 – 22 – 46.5 dB dB 0.256 0.256 0.256 256 256 256 kHz kHz kHz ● ● ● 0.256 0.256 0.256 25.6 25.6 25.6 kHz kHz kHz VS = 3V, RFIL = 100k VS = 4.75V, RFIL = 100k VS = ±5V, RFIL = 100k ● ● ● –3 –3 –3 ±2 ±2 ±2 5.5 5.5 5.5 % % % Cutoff Frequency Accuracy, HS Mode fC = 256kHz VS = 3V, RFIL = 10k VS = 4.75V, RFIL = 10k VS = ±5V, RFIL = 10k ● ● ● –3 –3 –3 ±2 ±2 ±2 6 6 6 % % % Cutoff Frequency Accuracy, LP Mode fC = 25.6kHz VS = 2.7V, RFIL = 100k VS = 4.75V, RFIL = 100k VS = ±5V, RFIL = 100k ● ● ● –4 –4 –4 ±3 ±3 ±3 7 7 7 % % % Cutoff Frequency Temperature Coefficient (Note 3) ● Passband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Test Frequency = 2.56kHz (0.1 • fC) Test Frequency = 12.8kHz (0.5 • fC) ● ● – 0.2 –1.0 – 0.03 – 0.72 0.2 – 0.25 dB dB Stopband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Test Frequency = 51.2kHz (2 • fC) Test Frequency = 102.4kHz (4 • fC) ● ● –13.6 – 34.7 –10 – 31 dB dB Passband Gain, HS Mode, fC = 256kHz VS = 4.75V, RFIL = 10k Test Frequency = 25.6kHz (0.1 • fC) Test Frequency = 128kHz (0.5 • fC) ● ● – 0.03 – 0.72 0.2 – 0.5 dB dB Stopband Gain, HS Mode, fC = 256kHz VS = 4.75V, RFIL = 10k Test Frequency = 400kHz (1.56 • fC) Test Frequency = 500kHz (1.95 • fC) ● ● – 8.3 – 13 –6 –10.5 dB dB Passband Gain, LP Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Test Frequency = 2.56kHz (0.1 • fC) Test Frequency = 12.8kHz (0.5 • fC) ● ● – 0.03 – 0.72 0.2 – 0.25 dB dB Stopband Gain, LP Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Test Frequency = 51.2kHz (2 • fC) Test Frequency = 102.4kHz (4 • fC) ● ● – 13.6 – 34.7 –11 – 32 dB dB – 0.2 – 0.5 – 0.25 – 0.6 LTC1563-3 Transfer Function Characteristics Note 1: Absolute Maximum Ratings are those value beyond which the life of a device may be impaired. Note 2: The minimum cutoff frequency of the LTC1563 is arbitrarily listed as 256Hz. The limit is arrived at by setting the maximum resistor value limit at 10MΩ. The LTC1563 can be used with even larger valued resistors. When using very large values of resistance careful layout and thorough 4 ±1 – 0.2 –1.1 – 0.2 –1.0 ppm/°C assembly practices are required. There may also be greater DC offset at high temperatures when using such large valued resistors. Note 3: The cutoff frequency temperature drift at low frequencies is as listed. At higher cutoff frequencies (approaching 25.6kHz in low power mode and approaching 256kHz in high speed mode) the internal amplifier’s bandwidth can effect the cutoff frequency. At these limits the cutoff frequency temperature drift is ±15ppm/°C. 156323fa LTC1563-2/LTC1563-3 U W TYPICAL PERFOR A CE CHARACTERISTICS 3.4 5.5 5.5 VS = SINGLE 3.3V 3.0 2.8 HS MODE 2.6 LP MODE 2.4 5.0 OUTPUT VOLTAGE (V) 5.0 OUTPUT VOLTAGE (V) 4.5 HS MODE 4.0 LP MODE 3.5 4.5 HS MODE 4.0 LP MODE 3.5 2.2 3.0 3.0 2.0 100 1k 10k 100k LOAD RESISTANCE—LOAD TO GROUND (Ω) 2.5 100 1k 10k 100k LOAD RESISTANCE—LOAD TO GROUND (Ω) 2.5 100 1k 10k 100k LOAD RESISTANCE—LOAD TO GROUND (Ω) 1563 G01 1563 G02 1563 G03 Output Voltage Swing Low vs Load Resistance Output Voltage Swing Low vs Load Resistance Output Voltage Swing Low vs Load Resistance 0.025 0.025 –4.3 VS = SINGLE 3.3V VS = SINGLE 5V HS MODE 0.015 LP MODE –4.4 0.020 OUTPUT VOLTAGE (V) 0.020 VS = ± 5V HS MODE 0.010 0.005 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) VS = ±5V VS = SINGLE 5V 3.2 OUTPUT VOLTAGE (V) Output Voltage Swing High vs Load Resistance Output Voltage Swing High vs Load Resistance Output Voltage Swing High vs Load Resistance LP MODE 0.015 0.010 –4.5 –4.6 –4.7 HS MODE –4.8 0.005 –4.9 0 1k 10k 100k 100 LOAD RESISTANCE—LOAD TO GROUND (Ω) 1563 G04 1563 G05 –40 THD + Noise vs Input Voltage –40 –40 3.3V SUPPLY 3.3V SUPPLY 3.3V SUPPLY 5V SUPPLY –60 ±5V SUPPLY –70 –80 fC = 25.6kHz LOW POWER MODE fIN = 5kHz –90 0.1 1 INPUT VOLTAGE (VP-P) –50 5V SUPPLY –60 ±5V SUPPLY –70 –80 fC = 25.6kHz HIGH SPEED MODE fIN = 5kHz –90 10 1563 G07 (THD + NOISE)/SIGNAL (dB) –50 (THD + NOISE)/SIGNAL (dB) –50 (THD + NOISE)/SIGNAL (dB) 1563 G06 THD + Noise vs Input Voltage THD + Noise vs Input Voltage –100 LP MODE –5.0 100 1k 10k 100k LOAD RESISTANCE—LOAD TO GROUND (Ω) 0 1k 10k 100k 100 LOAD RESISTANCE—LOAD TO GROUND (Ω) –100 0.1 1 INPUT VOLTAGE (VP-P) 5V SUPPLY –60 ±5V SUPPLY –70 –80 fC = 256kHz HIGH SPEED MODE fIN = 50kHz –90 10 1563 G08 –100 0.1 1 INPUT VOLTAGE (VP-P) 10 1563 G09 156323fa 5 LTC1563-2/LTC1563-3 U W TYPICAL PERFOR A CE CHARACTERISTICS THD + Noise vs Input Frequency THD + Noise vs Input Frequency –40 –60 –70 1VP-P –80 2VP-P –90 VS = SINGLE 3.3V HIGH SPEED MODE fC = 25.6kHz –70 (THD + NOISE)/SIGNAL (dB) VS = SINGLE 3.3V LOW POWER MODE fC = 25.6kHz (THD + NOISE)/SIGNAL (dB) (THD + NOISE)/SIGNAL (dB) –60 THD + Noise vs Input Frequency 1VP-P –80 2VP-P –90 VS = SINGLE 3V HIGH SPEED MODE fC = 256kHz –50 –60 –70 1VP-P –80 2VP-P –90 1 10 INPUT FREQUENCY (kHz) –100 20 1 10 INPUT FREQUENCY (kHz) 1563 G10 1VP-P –80 2VP-P –90 –70 1VP-P –80 2VP-P –90 3VP-P 1 20 –100 1563 G13 20 –100 (THD + NOISE)/SIGNAL (dB) –80 2VP-P 5VP-P –90 1 10 INPUT FREQUENCY (kHz) 100 200 1563 G15 THD + Noise vs Input Frequency –40 –60 1VP-P 2VP-P –80 THD + Noise vs Input Frequency THD + Noise vs Input Frequency VS = ± 5V LOW POWER MODE fC = 25.6kHz 1VP-P –70 1563 G14 –60 –70 –60 3VP-P 10 INPUT FREQUENCY (kHz) 1 VS = SINGLE 5V HIGH SPEED MODE fC = 256kHz –50 –90 3VP-P 10 INPUT FREQUENCY (kHz) 100 200 –40 VS = SINGLE 5V HIGH SPEED MODE fC = 25.6kHz (THD + NOISE)/SIGNAL (dB) (THD + NOISE)/SIGNAL (dB) (THD + NOISE)/SIGNAL (dB) –70 10 INPUT FREQUENCY (kHz) THD + Noise vs Input Frequency –60 VS = SINGLE 5V LOW POWER MODE fC = 25.6kHz 1 1563 G12 THD + Noise vs Input Frequency –60 (THD + NOISE)/SIGNAL (dB) –100 1563 G11 THD + Noise vs Input Frequency –100 20 VS = ± 5V HIGH SPEED MODE fC = 25.6kHz –70 (THD + NOISE)/SIGNAL (dB) –100 1VP-P –80 2VP-P 5VP-P –90 VS = ± 5V HIGH SPEED MODE fC = 256kHz –50 –60 1VP-P –70 2VP-P –80 –90 –100 1 10 INPUT FREQUENCY (kHz) 20 1563 G16 –100 1 10 INPUT FREQUENCY (kHz) 20 1563 G17 –100 5VP-P 1 10 INPUT FREQUENCY (kHz) 100 200 1563 G18 156323fa 6 LTC1563-2/LTC1563-3 U W TYPICAL PERFOR A CE CHARACTERISTICS THD + Noise vs Output Load –80 LP MODE, 2VP-P SIGNAL –85 –90 HS MODE, 3VP-P SIGNAL HS MODE, 2VP-P SIGNAL –75 2VP-P, 50kHz 2VP-P, 20kHz –80 –85 3VP-P, 50kHz –90 –95 –95 –100 –100 0 1 2 3 4 5 6 7 8 9 10 OUTPUT LOAD RESISTANCE—LOAD TO GROUND (kΩ) 60 –70 3VP-P, 20kHz VS = SINGLE 5V HIGH SPEED MODE fC = 256kHz fIN = 20kHz, 50kHz –80 LP MODE, 2VP-P SIGNAL –85 HS MODE, 2VP-P SIGNAL –90 –95 –100 0 1 2 3 4 5 6 7 8 9 10 OUTPUT LOAD RESISTANCE—LOAD TO GROUND (kΩ) 1 10 fC (Hz) 100 1000 fC = 256kHz 0 –10 2VP-P, 50kHz –20 –80 2VP-P, 20kHz –85 5VP-P, 50kHz –90 VS = ± 5V HIGH SPEED MODE fC = 256kHz fIN = 20kHz, 50kHz –30 LTC1563-2 LTC1563-3 –40 –50 –60 2VP-P, 20kHz –70 –80 –100 0 1 2 3 4 5 6 7 8 9 10 OUTPUT LOAD RESISTANCE—LOAD TO GROUND (kΩ) –90 10k 100k 1M 10M FREQUENCY (Hz) 100M 1563 G24 1563 G23 Crosstalk Rejection vs Frequency Crosstalk Rejection vs Frequency –60 –60 DUAL SECOND ORDER BUTTERWORTH fC = 25.6kHz HS OR LP MODE DUAL SECOND ORDER BUTTERWORTH fC = 256kHz HIGH SPEED MODE –70 CROSSTALK (dB) –70 CROSSTALK (dB) 10 Stopband Gain vs Input Frequency –75 1563 G22 –80 –90 –100 –110 20 10 –95 HS MODE, 5VP-P SIGNAL HS MODE 1563 G21 –70 (THD + NOISE)/SIGNAL (dB) (THD + NOISE)/SIGNAL (dB) LP MODE, 5VP-P SIGNAL 30 THD + Noise vs Output Load VS = ± 5V fC = 25.6kHz fIN = 5kHz LP MODE 40 1563 G20 THD + Noise vs Output Load –75 TA = 25°C 50 0k 0.1 0 1 2 3 4 5 6 7 8 9 10 OUTPUT LOAD RESISTANCE—LOAD TO GROUND (kΩ) 1563 G19 –70 TOTAL INTEGRATED NOISE (µVRMS) –75 VS = SINGLE 5V fC = 25.6kHz fIN = 5kHz GAIN (dB) LP MODE, 3VP-P SIGNAL (THD + NOISE)/SIGNAL (dB) (THD + NOISE)/SIGNAL (dB) –70 Output Voltage Noise vs Cutoff Frequency THD + Noise vs Output Load –80 –90 –100 1 10 FREQUENCY (kHz) 100 1563 G25 –110 1k 10k 100k FREQUENCY (Hz) 1M 1563 G26 156323fa 7 LTC1563-2/LTC1563-3 U U U PIN FUNCTIONS LP (Pin 1): Low Power. The LTC1563-X has two operating modes: Low Power and High Speed. Most applications will use the High Speed operating mode. Some lower frequency, lower gain applications can take advantage of the Low Power mode. When placed in the Low Power mode, the supply current is nearly an order of magnitude lower than the High Speed mode. Refer to the Applications Information section for more information on the Low Power mode. LPA, LPB (Pins 6, 15): Lowpass Output. These pins are the rail-to-rail outputs of an op amp. Each output is designed to drive a nominal net load of 5kΩ and 20pF. Refer to the Applications Information section for more details on output loading effects. The LTC1563-X is in the High Speed mode when the LP input is at a logic high level or is open-circuited. A small pull-up current source at the LP input defaults the LTC1563-X to the High Speed mode if the pin is left open. The part is in the Low Power mode when the pin is pulled to a logic low level or connected to V –. AGND (Pin 7): Analog Ground. The AGND pin is the midpoint of an internal resistive voltage divider developing a potential halfway between the V + and V – pins. The equivalent series resistance is nominally 10kΩ. This serves as an internal ground reference. Filter performance will reflect the quality of the analog signal ground. An analog ground plane surrounding the package is recommended. The analog ground plane should be connected to any digital ground at a single point. Figures 1 and 2 show the proper connections for dual and single supply operation. SA, SB (Pins 2, 11): Summing Pins. These pins are a summing point for signals fed forward and backward. Capacitance on the SA or SB pin will cause excess peaking of the frequency response near the cutoff frequency. The three external resistors for each section should be located as close as possible to the summing pin to minimize this effect. Refer to the Applications Information section for more details. V –, V + (Pins 8, 16): The V – and V + pins should be bypassed with 0.1µF capacitors to an adequate analog ground or ground plane. These capacitors should be connected as closely as possible to the supply pins. Low noise linear supplies are recommended. Switching supplies are not recommended as they will decrease the filter’s dynamic range. Refer to Figures 1 and 2 for the proper connections for dual and single supply operation. NC (Pins 3, 5, 10, 12, 14): These pins are not connected internally. For best performance, they should be connected to ground. EN (Pin 9): ENABLE. When the EN input goes high or is open-circuited, the LTC1563-X enters a shutdown state and only junction leakage currents flow. The AGND pin, the LPA output and the LPB output assume high impedance states. If an input signal is applied to a complete filter circuit while the LTC1563-X is in shutdown, some signal will normally flow to the output through passive components around the inactive part. INVA, INVB (Pins 4, 13): Inverting Input. Each of the INV pins is an inverting input of an op amp. Note that the INV pins are high impedance, sensitive nodes of the filter and very susceptible to coupling of unintended signals. Capacitance on the INV nodes will also affect the frequency response of the filter sections. For these reasons, printed circuit connections to the INV pins must be kept as short as possible. A small internal pull-up current source at the EN input defaults the LTC1563 to the shutdown state if the EN pin is left floating. Therefore, the user must connect the EN pin to V – (or a logic low) to enable the part for normal operation. 156323fa 8 LTC1563-2/LTC1563-3 U U U PIN FUNCTIONS Dual Supply Power and Ground Connections Single Supply Power and Ground Connections LTC1563-X ANALOG GROUND PLANE 1 2 3 4 5 6 7 8 V– LTC1563-X 16 V+ LP SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN ANALOG GROUND PLANE V+ 15 0.1µF 1 2 14 3 13 4 12 5 11 6 10 7 + 9 8 0.1µF V+ LP SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN 16 15 V+ 0.1µF 14 13 12 11 10 9 0.1µF SINGLE POINT SYSTEM GROUND SINGLE POINT SYSTEM GROUND DIGITAL GROUND PLANE (IF ANY) DIGITAL GROUND PLANE (IF ANY) 1563 PF02 1563 PF01 W BLOCK DIAGRA R21 R22 VOUT R11 R31 R12 R32 VIN + 16 V C1B C1A SHUTDOWN SWITCH 2 SA 20k 4 INVA AGND 7 C2A AGND 20k SHUTDOWN SWITCH 8 V– 9 EN 1 LP – + 11 SB 6 LPA 13 INVB C2B AGND – + 15 LPB AGND LTC1563-X PATENT PENDING 1563 BD 156323fa 9 LTC1563-2/LTC1563-3 U W U U APPLICATIONS INFORMATION Functional Description The LTC1563-2/LTC1563-3 are a family of easy-to-use, 4th order lowpass filters with rail-to-rail operation. The LTC1563-2, with a single resistor value, gives a unity-gain filter approximating a Butterworth response. The LTC1563-3, with a single resistor value, gives a unity-gain filter approximating a Bessel (linear phase) response. The proprietary architecture of these parts allows for a simple unity-gain resistor calculation: R = 10k(256kHz/fC) where fC is the desired cutoff frequency. For many applications, this formula is all that is needed to design a filter. For example, a 50kHz filter requires a 51.2k resistor. In practice, a 51.1k resistor would be used as this is the closest E96, 1% value available. The LTC1563-X is constructed with two 2nd order sections. The output of the first section (section A) is simply fed into the second section (section B). Note that section A and section B are similar, but not identical. The parts are designed to be simple and easy to use. By simply utilizing different valued resistors, gain, other transfer functions and higher cutoff frequencies are achieved. For these applications, the resistor value calculation gets more difficult. The tables of formulas provided later in this section make this task much easier. For best results, design these filters using FilterCAD Version 3.0 (or newer) or contact the Linear Technology Filter Applications group for assistance. Cutoff Frequency (fC) and Gain Limitations The LTC563-X has both a maximum fC limit and a minimum fC limit. The maximum fC limit (256kHz in High Speed mode and 25.6kHz in the Low Power mode) is set by the speed of the LTC1563-X’s op amps. At the maximum fC, the gain is also limited to unity. A minimum fC is dictated by the practical limitation of reliably obtaining large valued, precision resistors. As the desired fC decreases, the resistor value required increases. When fC is 256Hz, the resistors are 10M. Obtaining a reliable, precise 10M resistance between two points on a printed circuit board is somewhat difficult. For example, a 10M resistor with only 200MΩ of stray, layout related resistance in parallel, yields a net effective resistance of 9.52M and an error of – 5%. Note that the gain is also limited to unity at the minimum fC. At intermediate fC, the gain is limited by one of the two reasons discussed above. For best results, design filters with gain using FilterCAD Version 3 (or newer) or contact the Linear Technology Filter Applications Group for assistance. While the simple formula and the tables in the applications section deliver good approximations of the transfer functions, a more accurate response is achieved using FilterCAD. FilterCAD calculates the resistor values using an accurate and complex algorithm to account for parasitics and op amp limitations. A design using FilterCAD will always yield the best possible design. By using the FilterCAD design tool you can also achieve filters with cutoff frequencies beyond 256kHz. Cutoff frequencies up to 360kHz are attainable. Contact the Linear Technology Filter Applications Group for a copy the FilterCAD software. FilterCAD can also be downloaded from our website at www.linear.com. DC Offset, Noise and Gain Considerations The LTC1563-X is DC offset trimmed in a 2-step manner. First, section A is trimmed for minimum DC offset. Next, section B is trimmed to minimize the total DC offset (section A plus section B). This method is used to give the minimum DC offset in unity gain applications and most higher gain applications. For gains greater than unity, the gain should be distributed such that most of the gain is taken in section A, with section B at a lower gain (preferably unity). This type of gain distribution results in the lowest noise and lowest DC offset. For high gain, low frequency applications, all of the gain is taken in section A, with section B set for unity-gain. In this configuration, the noise and DC offset is dominated by those of section A. At higher frequencies, the op amps’ finite bandwidth limits the amount of gain that section A can reliably achieve. The gain is more evenly distributed in this case. The noise and DC offset of section A is now multiplied by the gain of section B. The result is slightly higher noise and offset. 156323fa 10 LTC1563-2/LTC1563-3 U W U U APPLICATIONS INFORMATION Resistive loading affects the maximum output signal swing and signal distortion. If the output load is excessive, the output swing is reduced and distortion is increased. All of the output voltage swing testing on the LTC1563-X is done with R22 = 100k and a 10k load resistor. For best undistorted output swing, the output load resistance should be greater than 10k. Capacitive loading on the output reduces the stability of the op amp. If the capacitive loading is sufficiently high, the stability margin is decreased to the point of oscillation at the output. Capacitive loading should be kept below 30pF. Good, tight layout techniques should be maintained at all times. These parts should not drive long traces and must never drive a long coaxial cable. When probing the LTC1563-X, always use a 10x probe. Never use a 1x probe. A standard 10x probe has a capacitance of 10pF to 15pF while a 1x probe’s capacitance can be as high as 150pF. The use of a 1x probe will probably cause oscillation. For larger capacitive loads, a series isolation resistor can be used between the part and the capacitive load. If the load is too great, a buffer must be used. Layout Precautions The LTC1563-X is an active RC filter. The response of the filter is determined by the on-chip capacitors and the external resistors. Any external, stray capacitance in parallel with an on-chip capacitor, or to an AC ground, can alter the transfer function. Capacitance to an AC ground is the most likely problem. Capacitance on the LPA or LPB pins does not affect the transfer function but does affect the stability of the op amps. Capacitance on the INVA and INVB pins will affect the transfer function somewhat and will also affect the stability of the op amps. Capacitance on the SA and SB pins alters the transfer function of the filter. These pins are the most sensitive to stray capacitance. Stray capacitance on these pins results in peaking of the frequency response To minimize the effects of parasitic layout capacitance, all of the resistors for section A should be placed as close as possible to the SA pin. Place the R31 resistor first so that it is as close as possible to the SA pin on one end and as close as possible to the INVA pin on the other end. Use the same strategy for the layout of section B, keeping all of the resistors as close as possible to the SB node and first placing R32 between the SB and INVB pins. It is also best if the signal routing and resistors are on the same layer as the part without any vias in the signal path. Figure 1 illustrates a good layout using the LTC1563-X with surface mount 0805 size resistors. An even tighter layout is possible with smaller resistors. R11 VIN LTC1563-X VOUT R32 R22 The op amps of the LTC1563-X have a rail-to-rail output stage. To obtain maximum performance, the output loading effects must be considered. Output loading issues can be divided into resistive effects and capacitive effects. near the cutoff frequency. Poor layout can give 0.5dB to 1dB of excess peaking. R21 R31 Output Loading: Resistive and Capacitive R12 1653 F01 Figure 1. PC Board Layout Single Pole Sections and Odd Order Filters The LTC1563 is configured to naturally form even ordered filters (2nd, 4th, 6th and 8th). With a little bit of work, single pole sections and odd order filters are easily achieved. To form a single pole section you simply use the op amp, the on-chip C1 capacitor and two external resistors as shown in Figure 2. This gives an inverting section with the gain set by the R2-R1 ratio and the pole set by the R2-C1 time constant. You can use this pole with a 2nd order section to form a noninverting gain 3rd order filter or as a stand alone inverting gain single pole filter. Figure 3 illustrates another way of making odd order filters. The R1 input resistor is split into two parts with an additional capacitor connected to ground in between the resistors. This “TEE” network forms a single real pole. RB1 156323fa 11 LTC1563-2/LTC1563-3 U U W U APPLICATIONS INFORMATION should be much larger than RA1 to minimize the interaction of this pole with the 2nd order section. This circuit is useful in forming dual 3rd order filters and 5th order filters with a single LTC1563 part. By cascading two parts, 7th order and 9th order filters are achieved. R1 RA1 RB1 R2 R3 CP S INV R2 – VOUT VIN C2 (OPEN) + S INV C1 AGND LP 1/2 LTC1563 – C2 RA1 ≈ + 1563 F03 RB1 10 FP = AGND 2π • ( 1 RA1 • RB1 ) RA1 + RB1 1/2 LTC1563 DC GAIN = –R2 R1 FP = LP C1 CP Figure 3 LTC1563-2: C1A = 53.9pF, C1B = 39.2pF LTC1563-3: C1A = 35pF, C1B = 26.8pF 1 2π • R2 • C1 1563 F02 Figure 2 You can also use the TEE network in both sections of the part to make a 6th order filter. This 6th order filter does not conform exactly to the textbook responses. Textbook responses (Butterworth, Bessel, Chebyshev etc.) all have three complex pole pairs. This filter has two complex pole pairs and two real poles. The textbook response always has one section with a low Q value between 0.5 and 0.6. By replacing this low Q section with two real poles (two real poles are the same mathematically as a complex pole pair with a Q of 0.5) and tweaking the Q of the other two complex pole pair sections you end up with a filter that is indistinguishable from the textbook filter. The Typical Applications section illustrates a 100kHz, 6th order pseudoButterworth filter. FilterCAD is a valuable tool for custom filter design and tweaking textbook responses. What To Do with an Unused Section If the LTC1563 is used as a 2nd or 3rd order filter, one of the sections is not used. Do not leave this section unconnected. If the section is left unconnected, the output is left to float and oscillation may occur. The unused section should be connected as shown in Figure 4 with the INV pin connected to the LP pin and the S pin left open. (OPEN) S INV C1 LP – C2 + AGND 1/2 LTC1563 1563 F04 Figure 4 156323fa 12 LTC1563-2/LTC1563-3 U U W U APPLICATIONS INFORMATION 4th Order Filter Responses Using the LTC1563-2 10 LTC1563-2 2 3 R31 4 5 R21 6 7 R11 8 16 V+ LP SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN 0 VOUT R22 15 –20 14 R32 13 GAIN (dB) 1 12 11 10 –40 BUTTERWORTH 0.5dB RIPPLE CHEBYSHEV 0.1dB RIPPLE CHEBYSHEV –60 R12 9 –80 NORMALIZED TO fC = 1Hz –90 1 0.1 FREQUENCY (Hz) 1563 F05 VIN 10 1563 F05a Figure 5. 4th Order Filter Connections (Power Supply, Ground, EN and LP Connections Not Shown for Clarity). Table 1 Shows Resistor Values Figure 5a. Frequency Response 1.2 1 0 OUTPUT VOLTAGE (V) 1.0 GAIN (dB) –2 –4 –6 –8 BUTTERWORTH 0.5dB RIPPLE CHEBYSHEV 0.1dB RIPPLE CHEBYSHEV NORMALIZED TO fC = 1Hz –10 0.1 FREQUENCY (Hz) 0.8 0.6 BUTTERWORTH 0.5dB RIPPLE CHEBYSHEV 0.1dB RIPPLE CHEBYSHEV 0.4 0.2 0 1 2 NORMALIZED TO fC = 1Hz 0 0.5 1.0 1.5 2.0 TIME (s) 2.5 1563 F05b 3.0 1563 F05c Figure 5b. Passband Frequency Response Figure 5c. Step Response Table 1. Resistor Values, Normalized to 256kHz Cutoff Frequency (fC), Figure 5. The Passband Gain, of the 4th Order LTC1563-2 Lowpass Filter, Is Set to Unity. (Note 1) LP Mode Max fC HS Mode Max fC BUTTERWORTH 0.1dB RIPPLE CHEBYSHEV 0.5dB RIPPLE CHEBYSHEV 25.6kHz 15kHz 13kHz 256kHz 135kHz 113kHz R11 = R21 = 10k(256kHz/fC) 13.7k(256kHz/fC) 20.5k(256kHz/fC) R31 = 10k(256kHz/fC) 10.7k(256kHz/fC) 12.4k(256kHz/fC) R12 = R22 = 10k(256kHz/fC) 10k(256kHz/fC) 12.1k(256kHz/fC) R32 = 10k(256kHz/fC) 6.81k(256kHz/fC) 6.98k(256kHz/fC) Example: In HS mode, 0.1dB ripple Chebyshev, 100kHz cutoff frequency, R11 = R21 = 35k ≅ 34.8k (1%), R31 = 27.39k ≅ 27.4k (1%), R12 = R22 = 256k ≅ 255k (1%), R32 = 17.43k ≅ 17.4k (1%) Note 1: The resistor values listed in this table provide good approximations of the listed transfer functions. For the optimal resistor values, higher gain or other transfer functions, use FilterCAD Version 3.0 (or newer) or contact the Linear Technology Filter Applications group for assistance. 156323fa 13 LTC1563-2/LTC1563-3 U U W U APPLICATIONS INFORMATION 4th Order Filter Responses Using the LTC1563-3 10 LTC1563-3 2 3 R31 4 5 R21 6 7 R11 8 0 LP V+ SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN 16 15 VOUT R22 –20 14 13 GAIN (dB) 1 R32 12 –40 BESSEL TRANSITIONAL GAUSSIAN TO 12dB TRANSITIONAL GAUSSIAN TO 6dB 11 –60 10 R12 9 –80 NORMALIZED TO fC = 1Hz –90 0.1 1 FREQUENCY (Hz) 1563 F06 VIN 1563 F06a Figure 6. 4th Order Filter Connections (Power Supply, Ground, EN and LP Connections Not Shown for Clarity). Table 2 Shows Resistor Values Figure 6a. Frequency Response 1.2 1.05 BESSEL TRANSITIONAL GAUSSIAN TO 12dB TRANSITIONAL GAUSSIAN TO 6dB 0.8 0.6 BESSEL TRANSITIONAL GAUSSIAN TO 12dB TRANSITIONAL GAUSSIAN TO 6dB 0.4 0.2 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 1.0 0 10 1.00 NORMALIZED TO fC = 1Hz 0 0.5 1.0 1.5 2.0 TIME (s) 2.5 NORMALIZED TO fC = 1Hz 0.95 3.0 0 0.5 1.0 TIME (s) 1.5 1563 F06b 2.0 1563 F06c Figure 6b. Step Response Figure 6c. Step Response—Settling Table 2. Resistor Values, Normalized to 256kHz Cutoff Frequency (fC), Figure 6. The Passband Gain, of the 4th Order LTC1563-3 Lowpass Filter, Is Set to Unity. (Note 1) BESSEL TRANSITIONAL GAUSSIAN TO 6dB TRANSITIONAL GAUSSIAN TO 12dB LP Mode Max fC 25.6kHz 20kHz 21kHz HS Mode Max fC 256kHz 175kHz 185kHz R11 = R21 = 10k(256kHz/fC) 17.4k(256kHz/fC) 15k(256kHz/fC) R31 = 10k(256kHz/fC) 13.3k(256kHz/fC) 11.8k(256kHz/fC) R12 = R22 = 10k(256kHz/fC) 14.3k(256kHz/fC) 10.5k(256kHz/fC) R32 = 10k(256kHz/fC) 6.04k(256kHz/fC) 6.19k(256kHz/fC) Note 1: The resistor values listed in this table provide good approximations of the listed transfer functions. For the optimal resistor values, higher gain or other transfer functions, use FilterCAD Version 3.0 (or newer) or contact the Linear Technology Filter Applications group for assistance. 156323fa 14 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S ±5V, 2.3mA Supply Current, 20kHz, 4th Order, 0.5dB Ripple Chebyshev Lowpass Filter Frequency Response 10 LTC1563-2 2 3 169k 4 5 274k 274k 6 VIN 7 8 –5V 16 V+ LP SA LPB NC NC INVA 15 13 SB AGND NC V– 0 –10 0.1µF –20 95.3k 12 NC LPA 162k 14 INVB NC VOUT 5V GAIN (dB) 1 11 10 EN –40 –50 –60 162k 9 –30 –70 ENABLE –80 0.1µF 1563 TA03 –90 10 FREQUENCY (kHz) 1 100 1563 TA04 Single 3.3V, 2mA Supply Current, 20kHz 8th Order Butterworth Lowpass Filter 3.3V 0.1µF LTC1563-2 1 2 3 115k 4 5 137k 6 7 115k VIN 8 LP SA LPB NC NC INVA NC INVB NC LPA SB AGND NC V– EN LTC1563-2 210k 16 V+ 1 82.5k 15 2 3 14 75k 196k 13 4 210k 6 7 10 82.5k 9 LP V+ SA LPB NC NC INVA 5 12 11 0.1µF 8 INVB NC NC LPA SB AGND NC V– EN 16 15 158k VOUT 14 13 100k 12 11 10 9 158k 0.1µF 0.1µF 1563 TA05 ENABLE Frequency Response 10 0 –10 GAIN (dB) –20 –30 –40 –50 –60 –70 –80 –90 1 10 FREQUENCY (kHz) 100 1563 TA06 156323fa 15 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S 100kHz, 6th Order Pseudo-Butterworth Frequency Response 3.3V 2 3 R31 VIN RA1 3.16k RB1 29.4k C11 560pF 17.8k R21 32.4k 4 5 6 7 8 16 V+ LP SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN 15 0 R22 28.7k –10 –20 VOUT 14 13 R32 12 20.5k GAIN (dB) 1 10 0.1µF LTC1563-2 11 –30 –40 –50 –60 10 –70 9 –80 –90 0.1µF RA2 3.16k –100 10k RB2 25.5k 100k FREQUENCY (Hz) C12 560pF 1M 1563 TA07a 1563 TA07 TEXTBOOK BUTTERWORTH PSEUDO-BUTTERWORTH fO1 = 100kHz Q1 = 1.9319 fO1 = 100kHz Q1 = 1.9319 fO2 = 100kHz Q2 = 0.7071 fO2 = 100kHz Q2 = 0.7358 fO3 = 100kHz Q3 = 0.5176 fO3 = 100kHz Real Poles fO4 = 100kHz Real Poles The complex, 2nd order section of the textbook design with the lowest Q is replaced with two real first order poles. The Q of another section is slightly altered such that the final filter’s response is indistinguisable from a textbook Butterworth response. Other Pseudo Filter Response Coefficients (All fO Are Normalized for a 1Hz Filter Cutoff) BESSEL 0.1dB RIPPLE CHEBYSHEV 0.5dB RIPPLE CHEBYSHEV TRANSITIONAL GAUSSIAN TO 12dB TRANSITIONAL GAUSSIAN TO 6dB f O1 1.9070 1.0600 1.0100 2.1000 1.5000 Q1 1.0230 3.8500 5.3000 2.2000 2.8500 f O2 1.6910 0.8000 0.7200 1.2500 1.0500 Q2 0.6110 1.0000 1.2000 0.8000 0.9000 f O3 1.6060 0.6000 0.5000 1.2500 0.9000 f O4 1.6060 1.0000 0.8000 1.2500 0.9000 The fO and Q values listed above can be entered in FilterCAD’s Enhanced Design window as a custom response filter. After entering the coefficients, FilterCAD will produce a schematic of the circuit. The procedure is as follows: 1. After starting FilterCAD, select the Enhanced Design window. 2. Select the Custom Response and set the custom FC to 1Hz. 3. In the Coefficients table, go to the Type column and click on the types listed and set the column with two LP types and two LP1 types. This sets up a template of a 6th order filter with two 2nd order lowpass sections and two 1st order lowpass sections. 4. Enter the fO and Q coefficients as listed above. For a Butterworth filter, use the same coefficients as the example circuit above except set all of the fO to 1Hz. 5. Set the custom FC to the desired cutoff frequency. This will automatically multiply all of the fO coefficients. You have now finished the design of the filter and you can click on the frequency response or step response buttons to verify the filter’s response. 6. Click on the Implement button to go on to the filter implementation stage. 7. In the Enhanced Implement window, click on the Active RC button to choose the LTC1563-2 part. You are now done with the filter’s implementation. Click on the schematic button to view the resulting circuit. 156323fa 16 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S 22kHz, 5th Order, 0.1dB Ripple Chebyshev Lowpass Filter Driving the LTC1604, 16-Bit ADC 5V 0.1µF LTC1563-2 2 3 RB1 215k C11 560pF –5V 82.5k R21 5 243k 7 6 8 SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– 10µF 16 15 R22 137k 49.9Ω 560pF 14 13 R32 12 78.7k 2.2µF 47µF 11 10 EN 0.1µF 9 5V R12 137k + 10µF 1 A + LTC1604 AVDD IN 2 A – AV IN DD 3 V SHDN REF 4 REFCOMP CS 5 AGND CONVST 6 AGND RD 7 AGND BUSY 8 AGND + 35 5V 10Ω 36 33 10µF 32 µP CONTROL LINES 31 30 27 11 TO 26 16-BIT PARALLEL BUS 9 DV DD 10 DGND OVDD 34 V SS OGND 29 28 5V OR 3V + 10µF –5V 10µF + 1563 TA08 4096 Point FFT of the Output Data 0 fSAMPLE = 292.6kHz fIN = 20kHz SINAD = 85dB THD = –91.5dB –20 –40 AMPLITUDE (dB) VIN RA1 26.7k 4 V+ + R31 LP + 1 –60 –80 –100 –120 –140 0 36.58 73.15 109.73 FREQUENCY (kHz) 146.30 1563 TA08a 156323fa 17 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S 50kHz Wideband Bandpass 4th Order Bessel Lowpass at 128kHz with Two Highpass Poles at 11.7kHz Yields a Wideband Bandpass Centered at 50kHz 10 5V LTC1563-3 2 3 R31 C11 680pF R11 20k VIN 4 20k R21 5 20k 7 6 8 –5V LP V+ SA LPB NC INVA NC INVB NC NC LPA SB AGND NC V– EN 0.1µF 16 15 0 R22 20k –10 VOUT 14 13 R32 12 20k GAIN (dB) 1 11 –20 –30 –40 10 R12 20k 9 –50 C12 680pF 0.1µF –60 1k 1563 TA09 10k 100k FREQUENCY (Hz) 1M 1563 TA09a To design these wideband bandpass filters with the LTC1563, start with a 4th order lowpass filter and add two highpass poles with the input, AC coupling capacitors. The lowpass cutoff frequency and highpass pole frequencies depend on the specific application. Some experimentation of lowpass and highpass frequencies is required to achieve the desired response. FilterCAD does not directly support this configuration. Use the custom design window in FilterCAD get the desired response and then use FilterCAD to give the schematic for the lowpass portion of the filter. Calculate the two highpass poles using the following formulae: 1 1 fO (HPA ) = , fO (HPB ) = 2 • π • R11• C11 2 • π • R12 • C12 The design process is as follows: 1. After starting FilterCAD, select the Enhanced Design window. 2. Choose a 4th order Bessel or Butterworth lowpass filter response and set the cutoff frequency to the high frequency corner of the desired bandpass. 3. Click on the custom response button. This copies the lowpass coefficients into the custom design Coefficients table. 4. In the Coefficients table, the first two rows are the LP Type with the fO and Q as previously defined. Go to the third and fourth rows and click on the Type column (currently a hyphen is in this space). Change the Type of each of these rows to type HP1. This sets up a template of a 6th order filter with two 2nd order lowpass sections and two 1st order highpass sections. 5. Change the frequency of the highpass (HP1) poles to get the desired frequency response. 6. You may have to perform this loop several times before you close in on the correct response. 7. Once you have reached a satisfactory response, note the highpass pole frequencies. The HP1 highpass poles must now be removed from the Custom design coefficients table. After removing the highpass poles, click on the Implement button to go on to the filter implementation stage. 8. In the Enhanced Implement window, click on the Active RC button and choose the LTC1563-2 part. Click on the schematic button to view the resulting circuit. 9. You now have the schematic for the 4th order lowpass part of the design. Now calculate the capacitor values from the following formulae: C11 = 1 1 , C12 = 2 • π • R11• fO (HPA ) 2 • π • R12 • fO (HPB ) 156323fa 18 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S 150kHz, 0.5dB Ripple, 4th Order Chebyshev with 10dB of DC Gain 20 5V LTC1563-2 2 3 R31 R11 24.3k VIN 4 9.76k R21 5 6 76.8k 7 8 –5V V+ LP SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN 16 0 R22 21k 15 –10 14 VOUT 13 R32 12 12.7k GAIN (dB) 1 10 0.1µF –20 –30 –40 11 10 –50 R12 21k 9 –60 –70 10k 0.1µF 100k FREQUENCY (Hz) 1563 TA10 1M 1563 TA10a U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. GN Package 16-Lead Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) .045 ±.005 16 15 14 13 12 11 10 9 .254 MIN .009 (0.229) REF .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ± .0015 .150 – .157** (3.810 – 3.988) .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) 2 3 4 5 6 7 .0532 – .0688 (1.35 – 1.75) 8 .004 – .0098 (0.102 – 0.249) 0° – 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) .008 – .012 (0.203 – 0.305) TYP .0250 (0.635) BSC GN16 (SSOP) 0204 3. DRAWING NOT TO SCALE *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 156323fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 19 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S Single Supply, 10kHz, Bandpass Filter Maximum Fcenter = 120kHz (–3dB Bandwidth = Fcenter/10) V LTC1563-2 2 VIN 3 R1 31.6k 4 5 R2 4.99k 6 7 0.1µF 8 LP SA NC INVA NC LPA AGND V– 3 0.1µF 16 V+ 15 LPB 14 NC 13 INVB 12 NC 11 SB 10 NC 9 EN 0 R3 200k –3 VOUT –6 GAIN (dB) 1 Frequency Response + R4 200k –9 –12 –15 –18 –21 –24 5 1563 TA11 GAIN AT fCENTER = 31.6k R1 R2 = 4.99k 7.5 MAXIMUM GAIN = 120kHz/fCENTER 10 12.5 15 FREQUENCY (kHz) 1021 fCENTER • (fCENTER2 + 5 • 1011) Single Supply, 100kHz, Elliptic Lowpass Filter Maximum Fcutoff = 120kHz Frequency Response VOUT R1 32.4k R4 32.4k 2 R3 15k 3 R2 32.4k 5 4 6 7 0.1µF 8 LP SA NC INVA NC LPA AGND V– 0 0.1µF 16 V+ 15 LPB 14 NC 13 INVB 12 NC 11 SB 10 NC 9 EN –6 R5 32.4k –12 –18 GAIN (dB) 1 6 V+ LTC1563-2 VIN 20 1563 TA11a R3 = R4 = R R= 17.5 –24 –30 –36 R6 21k –42 CIN 27pF –48 –54 –60 1K 1563 TA12 10K 100K FREQUENCY (Hz) PASSBAND GAIN = 0dB STOPBAND ATTENUATION = 26dB AT 1.5X fCUTOFF CIN = 27pF R2 = R4 = R5 = R1 9 R1 = 3.24 • 10 fCUTOFF R3 = R1 2.16 1M 1563 TA12a R6 = R1 1.54 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1560-1 5-Pole Elliptic Lowpass, fC = 1MHz/0.5MHz No External Components, SO-8 LTC1562 Universal Quad 2-Pole Active RC 10kHz < fO < 150kHz LTC1562-2 Universal Quad 2-Pole Active RC 20kHz < fO < 300kHz LTC1569-6 Low Power 10-Pole Delay Equalized Elliptic Lowpass fC < 80kHz, One Resistor Sets fC, SO-8 LTC1569-7 10-Pole Delay Equalized Elliptic Lowpass fC < 256kHz, One Resistor Sets fC, SO-8 LTC1565-31 650kHz Continuous Time, Linear Phase Lowpass fC = 650kHz, Differential In/Out LTC1568 Very Low Noise 4th Order Filter Building Block fC < 10MHz 156323fa 20 Linear Technology Corporation LT 1205 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005