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Final Electrical Specifications
FEATURES
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LTC1563-2/LTC1563-3 Active RC, 4th Order Lowpass Filter Family January 2000 DESCRIPTION
The LTC(R)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).
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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: 36VRMS for fC = 25.6kHz, 60VRMS 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 = 1A (Typ) Continuous Time, Active RC Filter, No Clock
APPLICATIONS
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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.
TYPICAL APPLICATION
Single 3.3V, 2.56kHz to 256kHz Butterworth Lowpass Filter
3.3V 0.1F LTC1563-2 1 2 3 R R R VIN 1F fC = 256kHz 4 5 6 7 8 LP SA NC INVA NC LPA AGND V
-
10 0
V+ LPB NC INVB NC SB NC EN
16 15 14 13 12 11 10 9 R R
VOUT
GAIN (dB)
-10 -20 -30 -40 -50 -60 R = 1M fC = 2.56kHz R = 10k fC = 256kHz
R
-70 -80 1k 100k 10k FREQUENCY (Hz) 1M
1563 TA02
()
10k R
1563 TA01
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.
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Frequency Response
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LTC1563-2/LTC1563-3
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW LP 1 SA 2 NC 3 INVA 4 NC 5 LPA 6 AGND 7 V- 8 16 V + 15 LPB 14 NC 13 INVB 12 NC 11 SB 10 NC 9 EN
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 ............................................... 0C to 70C LTC1563I ............................................ - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1563-2CGN LTC1563-3CGN LTC1563-2IGN LTC1563-3IGN
GN PACKAGE 16-LEAD NARROW PLASTIC SSOP TJMAX = 150C, JA = 135C/ 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 q denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. 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 Positive Output Voltage Swing (LPB Pin) HS Mode Negative Output Voltage Swing (LPB Pin) HS Mode Positive Output Swing (LPB Pin) LP Mode Negative Output Swing (LPB Pin) LP Mode DC Offset Voltage, HS Mode (Section A Only) DC Offset Voltage, LP Mode (Section A Only) DC Offset Voltage, HS Mode (Input to Output, Sections A, B Cascaded) DC Offset Voltage, LP Mode (Input to Output, Sections A, B Cascaded) 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 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 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 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 VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 5V, fC = 25.6kHz, RFIL = 100k VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 5V, fC = 25.6kHz, RFIL = 100k VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 5V, fC = 25.6kHz, RFIL = 100k VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 5V, fC = 25.6kHz, RFIL = 100k
q q q q q q q q q q q q q q q q q q q q q q q q q q
MIN 3 2.7 2.9 4.55 4.8
TYP
MAX 11 11
UNITS V V V V V
2.95 4.7 4.9 0.015 0.02 - 4.95 0.05 0.05 - 4.9
2.6 4.55 4.8
2.65 4.65 4.9 0.01 0.015 - 4.95 1.5 1.0 1.5 2 2 2 1.5 1.0 1.5 2 2 2 0.05 0.05 - 4.9 3 3 3 4 4 5 3 3 3 5 5 6
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LTC1563-2/LTC1563-3
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. 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) DC Offset Voltage Drift, LP Mode (Input to Output, Sections A, B) AGND Voltage Power Supply Current, HS Mode CONDITIONS VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 5V, fC = 25.6kHz, RFIL = 100k VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 5V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 3V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 5V, fC = 25.6kHz, RFIL = 100k VS = 2.7V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 5V, fC = 25.6kHz, RFIL = 100k VS = 4.75V, fC = 25.6kHz, RFIL = 100k VS = 3V VS = 4.75V VS = 5V VS = 3V VS = 4.75V VS = 5V VS = 3V VS = 4.75V VS = 5V VS = 3V VS = 4.75V VS = 5V VS = 3V VS = 4.75V VS = 5V VS = 2.7V VS = 4.75V VS = 5V VS = 3V, RFIL = 100k VS = 4.75V, RFIL = 100k VS = 5V, RFIL = 100k VS = 3V, RFIL = 10k VS = 4.75V, RFIL = 10k VS = 5V, RFIL = 10k VS = 2.7V, RFIL = 100k VS = 4.75V, RFIL = 100k VS = 5V, RFIL = 100k Test Frequency = 2.56kHz (0.1 * fC) Test Frequency = 12.8kHz (0.5 * fC) MIN
q q q q q q q q q q q q q q q q q q q q q q q q q q
TYP 5 5 5 5 5 5
MAX
UNITS V/C V/C V/C V/C V/C V/C
2.35
2.375 8.0 10.5 15 1.0 1.4 2.3 1
2.40 14 17 23 1.8 2.5 3.5 20 0.8 1 1
V mA mA mA mA mA mA A V V V V V V
Power Supply Current, LP Mode
Shutdown Mode Supply Current EN Input Logic Low Level EN Input Logic High Level LP Logic Low Level LP Logic High Level LTC1563-2 Transfer Function Characteristics Cutoff Frequency Range, fC HS Mode Cutoff Frequency Range, fC LP Mode Cutoff Frequency Accuracy, HS Mode fC = 25.6kHz Cutoff Frequency Accuracy, HS Mode fC = 256kHz Cutoff Frequency Accuracy, LP Mode fC = 25.6kHz Cutoff Frequency Temperature Coefficient Passband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k
2.5 4.3 4.4 0.8 1 1 2.5 4.3 4.4 5 5 5 5 5 5 -1.5 -1.5 -1.5 -5 -5 -5 -3 -3 -3 - 0.2 - 0.3 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1 0 0 0.2 0.3 256 256 256 25.6 25.6 25.6 3.5 3.5 3.5 1.5 1.5 1.5 3 3 3
V V V V V V kHz kHz kHz kHz kHz kHz % % % % % % % % % ppm/C dB dB
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LTC1563-2/LTC1563-3
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. 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 Passband Gain, HS Mode, fC = 256kHz VS = 4.75V, RFIL = 10k Stopband Gain, HS Mode, fC = 256kHz VS = 4.75V, RFIL = 10k Passband Gain, LP Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Stopband Gain, LP Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k LTC1563-3 Transfer Function Characteristics Cutoff Frequency Range, fC HS Mode Cutoff Frequency Range, fC LP Mode Cutoff Frequency Accuracy, HS Mode fC = 25.6kHz Cutoff Frequency Accuracy, HS Mode fC = 256kHz Cutoff Frequency Accuracy, LP Mode fC = 25.6kHz Cutoff Frequency Temperature Coefficient Passband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Stopband Gain, HS Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Passband Gain, HS Mode, fC = 256kHz VS = 4.75V, RFIL = 10k Stopband Gain, HS Mode, fC = 256kHz VS = 4.75V, RFIL = 10k Passband Gain, LP Mode, fC = 25.6kHz VS = 4.75V, RFIL = 100k Stopband 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) Test Frequency = 51.2kHz (2 * fC) Test Frequency = 102.4kHz (4 * fC) Test Frequency = 25.6kHz (0.1 * fC) Test Frequency = 128kHz (0.5 * fC) Test Frequency = 400kHz (1.56 * fC) Test Frequency = 500kHz (1.95 * fC) Test Frequency = 2.56kHz (0.1 * fC) Test Frequency = 12.8kHz (0.5 * fC) Test Frequency = 51.2kHz (2 * fC) Test Frequency = 102.4Hz (4 * fC) VS = 3V VS = 4.75V VS = 5V VS = 2.7V VS = 4.75V VS = 5V VS = 3V, RFIL = 100k VS = 4.75V, RFIL = 100k VS = 5V, RFIL = 100k VS = 3V, RFIL = 10k VS = 4.75V, RFIL = 10 VS = 5V, RFIL = 10k VS = 2.7V, RFIL = 100k VS = 4.75V, RFIL = 100k VS = 5V, RFIL = 100k
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CONDITIONS Test Frequency = 51.2kHz (2 * fC) Test Frequency = 102.4kHz (4 * fC) Test Frequency = 25.6kHz (0.1 * fC) Test Frequency = 128kHz (0.5 * fC) Test Frequency = 400kHz (1.56 * fC) Test Frequency = 500kHz (1.95 * fC) Test Frequency = 2.56kHz (0.1 * fC) Test Frequency = 12.8kHz (0.5 * fC) Test Frequency = 51.2kHz (2 * fC) Test Frequency = 102.4kHz (4 * fC)
MIN
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TYP - 24 - 48 0 0 - 15.7 - 23.3
MAX - 21.5 - 46 0.2 0.5 -13.5 - 21.5 0.25 0.6 - 22 - 46.5 256 256 256 25.6 25.6 25.6
UNITS dB dB dB dB dB dB dB dB dB dB kHz kHz kHz kHz kHz kHz % % % % % % % % % ppm/C dB dB dB dB dB dB dB dB dB dB dB dB
- 0.2 - 0.5
- 0.25 - 0.6
0 - 0.02 - 24 - 48
5 5 5 5 5 5 -2 -2 -2 -2 -2 -2 -3 -3 -3 - 0.2 -1.0 2 2 2 2 2 2 3 3 3 1 - 0.03 - 0.72 -13.6 - 34.7 - 0.2 -1.1 - 0.03 - 0.72 - 8.3 - 13 - 0.2 -1.0 - 0.03 - 0.72 - 13.6 - 34.7
5.5 5.5 5.5 6 6 6 7 7 7 0.2 - 0.25 -10 - 31 0.2 - 0.5 -6 -10.5 0.2 - 0.25 -11 - 32
Note 1: Absolute Maximum Ratings are those value beyond which the life of a device may be impaired.
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LTC1563-2/LTC1563-3
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 5k 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 10k. 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 0.1F 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.
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LTC1563-2/LTC1563-3
PIN FUNCTIONS
LTC1563-X ANALOG GROUND PLANE 1 2 3 4 5 6 7 V- 0.1F 8 LP SA NC INVA NC LPA AGND V- V+ LPB NC INVB NC SB NC EN 16 15 14 13 12 11 10 9 V+ 0.1F
ANALOG GROUND PLANE 1 2 3 4 5 6 7 LTC1563-X LP SA NC INVA NC LPA AGND V- V+ LPB NC INVB NC SB NC EN 16 15 14 13 12 11 10 9 V+ 0.1F
SINGLE POINT SYSTEM GROUND
Figure 1. Dual Supply Power and Ground Connections
BLOCK DIAGRA
+ 16 V
SHUTDOWN SWITCH 20k AGND 7 20k SHUTDOWN SWITCH 8 V- AGND 2 SA C2A AGND 4 INVA 11 SB 6 LPA C2B AGND 13 INVB
9 1
EN LP LTC1563-X
PATENT PENDING
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+
-
+
-
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1F
8
DIGITAL GROUND PLANE (IF ANY)
1563 F01
SINGLE POINT SYSTEM GROUND
DIGITAL GROUND PLANE (IF ANY)
1563 F02
Figure 2. Single Supply Power and Ground Connections
R21 R11 VIN R31 R12 R32
R22 VOUT
C1A
C1B
15 LPB
1563 BD
LTC1563-2/LTC1563-3
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 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. 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 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 20M of stray, layout related resistance 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. 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. Output Loading: Resistive and Capacitive 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. 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.
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LTC1563-2/LTC1563-3
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. 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 near the cutoff frequency. Poor layout can give 0.5dB to 1dB of excess peaking. 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.
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LTC1563-2/LTC1563-3
TYPICAL APPLICATIO S
4th Order Filter Responses Using the LTC1563-2
LTC1563-2 1 2 3 R31 4 5 R21 6 7 R11 8 LP SA NC INVA NC LPA AGND V- 16 V+ LPB NC INVB NC SB NC EN 15 14 GAIN (dB) 13 12 11 10 9 R12 R32 R22 VOUT
VIN
Figure 3. 4th Order Filter Connections (Power Supply, Ground, EN and LP Connections Not Shown for Clarity). Table 1 Shows Resistor Values
1 0
1.0 1.2
-2
GAIN (dB)
OUTPUT VOLTAGE (V)
-4 -6 -8 BUTTERWORTH 0.5dB RIPPLE CHEBYSHEV 0.1dB RIPPLE CHEBYSHEV
NORMALIZED TO fC = 1Hz -10 0.1 FREQUENCY (Hz)
Figure 3b. Passband Frequency 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)
BUTTERWORTH LP Mode Max fC HS Mode Max fC R11 = R21 = R31 = R12 = R22 = R32 = 25.6kHz 256kHz 10k(256kHz/fC) 10k(256kHz/fC) 10k(256kHz/fC) 10k(256kHz/fC) 0.1dB RIPPLE CHEBYSHEV 15kHz 135kHz 13.7k(256kHz/fC) 10.7k(256kHz/fC) 10k(256kHz/fC) 6.81k(256kHz/fC) 0.5dB RIPPLE CHEBYSHEV 13kHz 113kHz 20.5k(256kHz/fC) 12.4k(256kHz/fC) 12.1k(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.
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-20
-40 BUTTERWORTH 0.5dB RIPPLE CHEBYSHEV 0.1dB RIPPLE CHEBYSHEV
-60
-80
1563 F03
NORMALIZED TO fC = 1Hz -90 0.1 1 FREQUENCY (Hz)
10
1563 F03a
Figure 3a. Frequency Response
0.8 0.6 0.4 0.2 0 BUTTERWORTH 0.5dB RIPPLE CHEBYSHEV 0.1dB RIPPLE CHEBYSHEV NORMALIZED TO fC = 1Hz 0 0.5 1.0 1.5 2.0 TIME (s) 2.5 3.0
1
2
1563 F03b
1563 F03C
Figure 3c. Step Response
9
LTC1563-2/LTC1563-3
TYPICAL APPLICATIO S
4th Order Filter Responses Using the LTC1563-3
10
LTC1563-3 1 2 3 R31 4 5 R21 6 7 R11 8 LP SA NC INVA NC LPA AGND V- V+ LPB NC INVB NC SB NC EN 16 15 14 13 12 11 10 9 R12 R32 GAIN (dB) R22 VOUT
VIN
Figure 4. 4th Order Filter Connections (Power Supply, Ground, EN and LP Connections Not Shown for Clarity). Table 2 Shows Resistor Values
1.2 1.0
OUTPUT VOLTAGE (V)
0.8 0.6 0.4 0.2 0 BESSEL TRANSITIONAL GAUSSIAN TO 12dB TRANSITIONAL GAUSSIAN TO 6dB NORMALIZED TO fC = 1Hz 0 0.5 1.0 1.5 2.0 TIME (s) 2.5 3.0
OUTPUT VOLTAGE (V)
Figure 4b. Step Response
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 LP Mode Max fC HS Mode Max fC R11 = R21 = R31 = R12 = R22 = R32 = 25.6kHz 256kHz 10k(256kHz/fC) 10k(256kHz/fC) 10k(256kHz/fC) 10k(256kHz/fC) TRANSITIONAL GAUSSIAN TO 6dB 20kHz 175kHz 17.4k(256kHz/fC) 13.3k(256kHz/fC) 14.3k(256kHz/fC) 6.04k(256kHz/fC) TRANSITIONAL GAUSSIAN TO 12dB 21kHz 185kHz 15k(256kHz/fC) 11.8k(256kHz/fC) 10.5k(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
U
0
-20
-40 BESSEL TRANSITIONAL GAUSSIAN TO 12dB TRANSITIONAL GAUSSIAN TO 6dB
-60
-80
1563 F04
NORMALIZED TO fC = 1Hz -90 0.1 1 FREQUENCY (Hz)
10
1563 F04a
Figure 4a. Frequency Response
1.05 BESSEL TRANSITIONAL GAUSSIAN TO 12dB TRANSITIONAL GAUSSIAN TO 6dB
1.00
0.95 0 0.5
NORMALIZED TO fC = 1Hz 1.0 TIME (s) 1.5 2.0
1563 F04c
1563 F04b
Figure 4c. Step Response--Settling
LTC1563-2/LTC1563-3
TYPICAL APPLICATIO S
5V, 2.3mA Supply Current, 20kHz, 4th Order, 0.5dB Ripple Chebyshev Lowpass Filter
LTC1563-2 1 2 3 162k 4 5 267k VIN 267k 6 7 -5V 0.1F
1563 TA03
LP SA NC INVA NC LPA AGND V-
16 V+ LPB NC INVB NC SB NC EN 15 14
GAIN (dB)
13 12 11 10 9
8
Single 3.3V, 2mA Supply Current, 20kHz 8th Order Butterworth Lowpass Filter
3.3V LTC1563-2 1 2 3 113k 4 5 133k 6 7 113k 8 LP SA NC INVA NC LPA AGND V- 16 V+ LPB NC INVB NC SB NC EN 15 14 13 12 11 10 9 80.6k 1F
1563 TA05
VIN ENABLE
1F
GAIN (dB)
U
Frequency Response
10 VOUT 5V 0.1F 0 -10 -20
158k
93.1k
-30 -40 -50 -60 -70 -80 -90 1 10 FREQUENCY (kHz) 100
1563 TA04
158k ENABLE
0.1F 205k 80.6k 1 2 3 191k 73.2k 4 5 205k 6 7 8
LTC1563-2 LP SA NC INVA NC LPA AGND V- V+ LPB NC INVB NC SB NC EN 16 15 14 13 12 11 10 9 97.6k 154k
0.1F VOUT
154k
Frequency Response
10 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 1 10 FREQUENCY (kHz) 100
1563 TA06
11
LTC1563-2/LTC1563-3
TYPICAL APPLICATIO S
Single 3.3V, 256kHz Bessel Lowpass Filter
3.3V LTC1563-3 1 2 3 10k 4 5 10k 10k VIN 1F
1563 TA07
LP SA NC INVA NC LPA AGND V-
V+ LPB NC INVB NC SB NC EN
16 15 14 13 12 11 10 9 10k ENABLE 10k 10k VOUT
GAIN (dB)
6 7 8
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 x 45 (0.38 0.10) 0.007 - 0.0098 (0.178 - 0.249) 0.016 - 0.050 (0.406 - 1.270) 0 - 8 TYP 0.229 - 0.244 (5.817 - 6.198) 0.150 - 0.157** (3.810 - 3.988) 0.053 - 0.068 (1.351 - 1.727) 0.004 - 0.0098 (0.102 - 0.249) 16 15 14 13 12 11 10 9
* 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
RELATED PARTS
PART NUMBER LTC1560-1 LTC1562 LTC1562-2 LTC1569-6 LTC1569-7 DESCRIPTION 5-Pole Elliptic Lowpass, fC = 1MHz/0.5MHz Universal Quad 2-Pole Active RC Universal Quad 2-Pole Active RC Low Power 10-Pole Delay Equalized Elliptic Lowpass 10-Pole Delay Equalized Elliptic Lowpass COMMENTS No External Components, SO-8 10kHz < fO < 150kHz 20kHz < fO < 300kHz fC < 80kHz, One Resistor Sets fC, SO-8 fC < 256kHz, One Resistor Sets fC, SO-8
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
U
U
Frequency Response
10 0 -10 -20 -30 -40 -50 10k
0.1F
100k FREQUENCY (Hz)
1M
1563 TA08
0.009 (0.229) REF
0.008 - 0.012 (0.203 - 0.305)
0.0250 (0.635) BSC
1
23
4
56
7
8
GN16 (SSOP) 1098
156323i LT/TP 0100 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 2000

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