Final Electrical Specifications LTC1563-2/LTC1563-3 Active RC, 4th Order Lowpass Filter Family January 2000 DESCRIPTION U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Extremely Easy to Use—A Single Resistor Value Sets the Cutoff Frequency (2.56kHz < fC < 256kHz) Extremely Flexible—Different Resistor Values Allow Arbitrary Transfer Functions with or without Gain (2.56kHz < fC < 256kHz) 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 Low Power Mode, fC < 25.6kHz, ISUPPLY =1mA (Typ) High Speed Mode, fC < 256kHz, ISUPPLY = 10mA (Typ) Shutdown Mode, ISUPPLY = 1µA (Typ) Continuous Time, Active RC Filter, No Clock 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: R = 10k (256kHz/fC); fC = Cutoff Frequency 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 (SO-8 footprint). U APPLICATIONS ■ ■ ■ ■ Replaces Discrete RC Active Filters and Modules Antialiasing Filters Smoothing or Reconstruction Filters Linear Phase Filtering for Data Communication Phase Locked Loops , LTC and LT are registered trademarks of Linear Technology Corporation. U ■ TYPICAL APPLICATION Frequency Response Single 3.3V, 2.56kHz to 256kHz Butterworth Lowpass Filter 0 3.3V 0.1µF LTC1563-2 3 R 4 5 R 6 7 8 VIN LP V+ SA LPB NC INVA NC INVB NC NC LPA SB AGND NC V – EN 1µF fC = 256kHz 16 15 VOUT 13 R = 10k fC = 256kHz –20 14 R 12 –30 R = 1M fC = 2.56kHz –40 –50 11 10 –60 9 ( ) 10k R R –10 GAIN (dB) 1 2 R 10 R –70 –80 1k 1563 TA01 100k 10k FREQUENCY (Hz) 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. 1M 1563 TA02 1 LTC1563-2/LTC1563-3 W U U W W W (Note 1) U ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION 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 ORDER PART NUMBER TOP VIEW LP 1 16 V + SA 2 15 LPB NC 3 14 NC INVA 4 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 EN GN PACKAGE 16-LEAD NARROW PLASTIC SSOP TJMAX = 150°C, θJA = 135°C/ W NOTE: PINS LABELED NC ARE NOT CONNECTED INTERNALLY AND SHOULD BE CONNECTED TO THE SYSTEM GROUND Consult factory 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 Total Supply Voltage (VS), HS Mode Total Supply Voltage (VS), LP Mode MIN ● 3 TYP MAX UNITS 11 V 11 V ● 2.7 Positive Output Voltage Swing (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 ● ● ● 2.9 4.55 4.8 Negative Output Voltage Swing (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 ● ● ● Positive Output Swing (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 ● ● ● Negative Output Swing (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 ±4 ±4 ±5 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 DC Offset Voltage, 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 ● ● ● ±2 ±2 ±2 ±5 ±5 ±6 mV mV mV 2 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 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 Drift, HS Mode (Input to Output, Sections A, B) CONDITIONS VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● MIN TYP 5 5 5 DC Offset Voltage Drift, LP Mode (Input to Output, Sections A, B) VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = ±5V, fC = 25.6kHz, RFIL = 100k ● ● ● 5 5 5 AGND Voltage VS = 4.75V, fC = 25.6kHz, RFIL = 100k ● 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 Power Supply Current, LP Mode 2.35 MAX UNITS µV/°C µV/°C µV/°C µV/°C µV/°C µV/°C 2.375 2.40 ● ● ● 8.0 10.5 15 14 17 23 mA mA mA 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 VS = 3V VS = 4.75V VS = ±5V ● ● ● 5 5 5 256 256 256 kHz kHz kHz Cutoff Frequency Range, fC LP Mode VS = 2.7V VS = 4.75V VS = ±5V ● ● ● 5 5 5 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 ● ● ● –1.5 –1.5 –1.5 ±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 1.5 1.5 1.5 % % % 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 % % % 2.5 4.3 4.4 V V V V 0.8 1 1 V V V V V V LTC1563-2 Transfer Function Characteristics Cutoff Frequency Temperature Coefficient Passband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k ±1 ● Test Frequency = 2.56kHz (0.1 • fC) Test Frequency = 12.8kHz (0.5 • fC) ● ● – 0.2 – 0.3 0 0 ppm/°C 0.2 0.3 dB dB 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 Stopband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k CONDITIONS Test Frequency = 51.2kHz (2 • fC) Test Frequency = 102.4kHz (4 • fC) ● ● MIN TYP – 24 – 48 MAX – 21.5 – 46 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) ● ● – 0.2 – 0.5 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 Stopband Gain, LP Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Test Frequency = 51.2kHz (2 • fC) Test Frequency = 102.4kHz (4 • fC) ● ● – 24 – 48 – 22 – 46.5 dB dB Cutoff Frequency Range, fC HS Mode VS = 3V VS = 4.75V VS = ±5V ● ● ● 5 5 5 256 256 256 kHz kHz kHz Cutoff Frequency Range, fC LP Mode VS = 2.7V VS = 4.75V VS = ±5V ● ● ● 5 5 5 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 –2 –2 ±2 ±2 ±2 5.5 5.5 5.5 % % % Cutoff Frequency Accuracy, HS Mode fC = 256kHz VS = 3V, RFIL = 10k VS = 4.75V, RFIL = 10 VS = ±5V, RFIL = 10k ● ● ● –2 –2 –2 ±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 ● ● ● –3 –3 –3 ±3 ±3 ±3 7 7 7 % % % – 0.2 –1.0 – 0.03 – 0.72 0.2 – 0.25 dB dB –13.6 – 34.7 –10 – 31 dB dB – 0.03 – 0.72 0.2 – 0.5 dB dB – 8.3 – 13 –6 –10.5 dB dB – 0.03 – 0.72 0.2 – 0.25 dB dB – 13.6 – 34.7 –11 – 32 dB dB – 0.25 – 0.6 UNITS dB dB LTC1563-3 Transfer Function Characteristics Cutoff Frequency Temperature Coefficient 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 = 102.4Hz (4 • fC) ● ● Note 1: Absolute Maximum Ratings are those value beyond which the life of a device may be impaired. 4 ±1 ● Passband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k – 0.2 –1.1 – 0.2 –1.0 ppm/°C LTC1563-2/LTC1563-3 U U U PIN FUNCTIONS LP (Pin 1): Low Power. The LTC1563-X has two operating modes. Most applications use the part’s 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. 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 –. 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. NC (Pins 3, 5, 10, 12, 14): These pins are not connected internally. For best performance, they should be connected to ground. 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. 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. 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. 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. 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. 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. 5 LTC1563-2/LTC1563-3 U U ANALOG GROUND PLANE 1 U PIN FUNCTIONS LTC1563-X 2 3 4 5 6 7 8 V– LTC1563-X V+ LP SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN 16 ANALOG GROUND PLANE V+ 15 0.1µF 1 2 14 3 13 4 12 5 11 6 10 7 + 9 8 1µF LP V+ 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 F02 1563 F01 Figure 1. Dual Supply Power and Ground Connections Figure 2. Single Supply Power and Ground Connections 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 6 1563 BD 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. in parallel, yields a net effective resistance of 952k 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. 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. By simply utilizing different valued resistors, gain and other transfer functions 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 FilterCADTM Version 3.0 (or newer) or contact the Linear Technology Filter Applications group for assistance. 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. Cutoff Frequency (fC) and Gain limitations Output Loading: Resistive and Capacitive 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. 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. 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 2.56kHz, the resistors are 1M. Obtaining a reliable, precise 1M resistance between two points on a printed circuit board is somewhat difficult. For example, a 1M resistor with 20MΩ of stray, layout related resistance 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. FilterCAD is trademark of Linear Technology Corporation. 7 LTC1563-2/LTC1563-3 U W U U APPLICATIONS INFORMATION 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. 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 near the cutoff frequency. Poor layout can give 0.5dB to 1dB of excess peaking. 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. 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. 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. 8 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S 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 0.1 1 FREQUENCY (Hz) 1563 F03 VIN 10 1563 F03a Figure 3. 4th Order Filter Connections (Power Supply, Ground, EN and LP Connections Not Shown for Clarity). Table 1 Shows Resistor Values Figure 3a. 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 F03b 3.0 1563 F03C Figure 3b. Passband Frequency Response Figure 3c. Step Response Table 1. Resistor Values, Normalized to 256kHz Cutoff Frequency (fC), Figure 3. 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. 9 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S 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 F04 VIN 1563 F04a Figure 4. 4th Order Filter Connections (Power Supply, Ground, EN and LP Connections Not Shown for Clarity). Table 2 Shows Resistor Values Figure 4a. 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 F04b 2.0 1563 F04c Figure 4b. Step Response Figure 4c. Step Response—Settling Table 2. Resistor Values, Normalized to 256kHz Cutoff Frequency (fC), Figure 4. 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. 10 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 162k 4 5 267k 267k 6 VIN 7 8 –5V 16 V+ LP SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– 15 VOUT 5V 158k 0 –10 0.1µF –20 14 13 93.1k GAIN (dB) 1 12 11 10 EN –40 –50 –60 158k 9 –30 –70 ENABLE –80 0.1µF –90 1563 TA03 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 113k 4 5 133k 6 7 113k VIN 8 LP SA LPB NC NC INVA NC INVB NC LPA SB AGND NC V– EN LTC1563-2 205k 16 V+ 1 80.6k 15 2 3 14 73.2k 191k 13 4 5 12 205k 11 6 7 10 80.6k 9 0.1µF 8 LP V+ SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN 16 15 154k VOUT 14 13 97.6k 12 11 10 9 154k 1µF 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 11 LTC1563-2/LTC1563-3 U TYPICAL APPLICATIO S Single 3.3V, 256kHz Bessel Lowpass Filter Frequency Response 3.3V LTC1563-3 2 3 10k 4 5 10k 6 7 10k 8 VIN LP V+ SA LPB NC NC INVA INVB NC NC LPA SB AGND NC V– EN 16 15 0 10k VOUT 14 13 –10 10k GAIN (dB) 1 10 0.1µF 12 11 –20 –30 10 10k 9 –40 ENABLE 1µF –50 10k 1563 TA07 100k FREQUENCY (Hz) 1M 1563 TA08 U PACKAGE DESCRIPTION GN Package 16-Lead Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) 0.189 – 0.196* (4.801 – 4.978) 0.015 ± 0.004 × 45° (0.38 ± 0.10) 0.007 – 0.0098 (0.178 – 0.249) 0.053 – 0.068 (1.351 – 1.727) 0.004 – 0.0098 (0.102 – 0.249) 16 15 14 13 12 11 10 9 0.009 (0.229) REF 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.008 – 0.012 (0.203 – 0.305) 0.0250 (0.635) BSC 0.229 – 0.244 (5.817 – 6.198) * 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 0.150 – 0.157** (3.810 – 3.988) 1 2 3 4 5 6 7 8 GN16 (SSOP) 1098 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 12 Linear Technology Corporation 156323i LT/TP 0100 4K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 2000