LTC1569-7 Linear Phase, DC Accurate, Tunable, 10th Order Lowpass Filter Furthermore, its root raised cosine response offers the optimum pulse shaping for PAM data communications. The filter attenuation is 50dB at 1.5 • fCUTOFF, 60dB at 2 • fCUTOFF, and in excess of 80dB at 6 • fCUTOFF. DC-accuracysensitive applications benefit from the 5mV maximum DC offset. FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ One External R Sets Cutoff Frequency Root Raised Cosine Response Up to 300kHz Cutoff on a Single 5V Supply Up to 150kHz Cutoff on a Single 3V Supply 10th Order, Linear Phase Filter in an SO-8 DC Accurate, VOS(MAX) = 5mV Low Power Modes Differential or Single-Ended Inputs 80dB CMRR (DC) 80dB Signal-to-Noise Ratio, VS = 5V Operates from 3V to ±5V Supplies U APPLICATIO S ■ ■ ■ Data Communication Filters for 3V Operation Linear Phase and Phase Matched Filters for I/Q Signal Processing Pin Programmable Cutoff Frequency Lowpass Filters U DESCRIPTIO The LTC®1569-7 is a 10th order lowpass filter featuring linear phase and a root raised cosine amplitude response. The high selectivity of the LTC1569-7 combined with its linear phase in the passband makes it suitable for filtering both in data communications and data acquisition sytems. The LTC1569-7 is the first sampled data filter which does not require an external clock yet its cutoff frequency can be set with a single external resistor with a typical accuracy of 3.5% or better. The external resistor programs an internal oscillator whose frequency is divided by either 1, 4 or 16 prior to being applied to the filter network. Pin 5 determines the divider setting. Thus, up to three cutoff frequencies can be obtained for each external resistor value. Using various resistor values and divider settings, the cutoff frequency can be programmed over a range of seven octaves. Alternatively, the cutoff frequency can be set with an external clock and the clock-to-cutoff frequency ratio is 32:1. The ratio of the internal sampling rate to the filter cutoff frequency is 64:1. The LTC1569-7 is fully tested for a cutoff frequency of 256kHz/128kHz with single 5V/3V supply although up to 300kHz cutoff frequencies can be obtained. The LTC1569-7 features power savings modes and it is available in an SO-8 surface mount package. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATION Frequency Response, fCUTOFF = 128kHz/32kHz/8kHz Single 3V Supply, 128kHz/32kHz/8kHz Lowpass Filter 3V 1 2 OUT IN – V+ 8 7 VOUT –20 REXT = 10k 3V 1µF LTC1569-7 3.48k 3 2k IN + GND RX 6 1µF V– DIV/CLK fCUTOFF = –80 1/1 100pF –100 128kHz (10k/REXT) 1, 4 OR 16 –60 1/4 5 EASY TO SET fCUTOFF: –40 3V 1/16 4 GAIN (dB) VIN 0 1569-7 TA01 1 10 100 FREQUENCY (kHz) 1000 1569-7 TA01a 1 LTC1569-7 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Total Supply Voltage ................................................ 11V Power Dissipation .............................................. 500mW Operating Temperature LTC1569C ............................................... 0°C to 70°C LTC1569I ............................................ – 40°C to 85°C Storage Temperature ............................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW IN + 1 8 OUT – 2 7 V+ GND 3 6 RX V– 4 5 DIV/CLK IN LTC1569CS8-7 LTC1569IS8-7 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 80°C/W (Note 6) 15697 1569I7 Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 3V (V + = 3V, V – = 0V), fCUTOFF = 128kHz, RLOAD = 10k unless otherwise specified. PARAMETER CONDITIONS Filter Gain VS = 5V, fCLK = 8.192MHz, fCUTOFF = 256kHz, VIN = 2.5VP-P, REXT = 5k, Pin 5 Shorted to Pin 4 fIN = 5120Hz = 0.02 • fCUTOFF fIN = 51.2kHz = 0.2 • fCUTOFF fIN = 128kHz = 0.5 • fCUTOFF fIN = 204.8kHz = 0.8 • fCUTOFF fIN = 256kHz = fCUTOFF, LTC1569C fIN = 256kHz = fCUTOFF, LTC1569I fIN = 384kHz = 1.5 • fCUTOFF fIN = 512kHz = 2 • fCUTOFF fIN = 768kHz = 3 • fCUTOFF VS = 2.7V, fCLK = 1MHz, fIN = 625Hz = 0.02 • fCUTOFF fIN = 6.25kHz = 0.2 • fCUTOFF fCUTOFF = 31.25kHz, VIN = 1VP-P, Pin 6 Shorted to Pin 4, External Clock fIN = 15.625kHz = 0.5 • fCUTOFF fIN = 25kHz = 0.8 • fCUTOFF fIN = 31.25kHz = fCUTOFF fIN = 46.875kHz = 1.5 • fCUTOFF fIN = 62.5kHz = 2 • fCUTOFF fIN = 93.75kHz = 3 • fCUTOFF Filter Phase VS = 2.7V, fCLK = 4MHz, fCUTOFF = 125kHz, Pin 6 Shorted to Pin 4, External Clock Filter Cutoff Accuracy when Self-Clocked REXT = 10.24k from Pin 6 to Pin 7, VS = 3V, Pin 5 Shorted to Pin 4 Filter Output DC Swing VS = 3V, Pin 3 = 1.11V fIN = 2500Hz = 0.02 • fCUTOFF fIN = 25kHz = 0.2 • fCUTOFF fIN = 62.5kHz = 0.5 • fCUTOFF fIN = 100kHz = 0.8 • fCUTOFF fIN = 125kHz = fCUTOFF fIN = 187.5kHz = 1.5 • fCUTOFF MIN TYP MAX UNITS ● ● ● ● ● ● ● ● ● – 0.10 – 0.25 – 0.50 – 1.1 – 5.7 – 6.2 0.00 – 0.15 – 0.41 – 0.65 – 3.8 – 3.8 – 58 – 62 – 67 0.10 – 0.05 – 0.25 – 0.40 – 2.3 – 2.0 – 48 – 54 – 64 dB dB dB dB dB dB dB dB dB ● ● ● ● ● ● ● ● – 0.08 – 0.25 – 0.50 – 0.75 – 3.3 0.00 – 0.15 – 0.40 – 0.65 – 3.15 – 57 – 60 – 66 0.12 – 0.05 – 0.30 – 0.50 – 3.0 – 52 – 54 – 58 dB dB dB dB dB dB dB dB ● ● ● ● – 114 78 – 85 155 –11 –112 80 – 83 158 – 95 –110 82 – 81 161 Deg Deg Deg Deg Deg Deg 125kHz ±1% 2.1 VP-P VP-P 3.9 VP-P VP-P 8.6 8.4 VP-P VP-P 8.0 VP-P ● 1.9 ● 3.7 LTC1569C ● LTC1569I ● VS = 5V, Pin 3 = 2V VS = ±5V 2 LTC1569-7 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 3V (V + = 3V, V – = 0V), fCLK = 4.096MHz, fCUTOFF = 128kHz, RLOAD = 10k unless otherwise specified. PARAMETER Output DC Offset (Note 2) CONDITIONS REXT = 10k, Pin 5 Shorted to Pin 4 Output DC Offset Drift Clock Pin Logic Thresholds when Clocked Externally Power Supply Current (Note 3) VS = 3V VS = 5V VS = ±5V MIN TYP ±2 ±6 ±15 REXT = 10k, Pin 5 Shorted to Pin 4 VS = 3V VS = 5V VS = ±5V – 25 – 25 ±25 µV/°C µV/°C µV/°C VS = 3V Min Logical “1” Max Logical “0” 2.6 0.5 V V VS = 5V Min Logical “1” Max Logical “0” 4.0 0.5 V V VS = ±5V Min Logical “1” Max Logical “0” 4.0 0.5 V V fCLK = 1.028MHz (10k from Pin 6 to Pin 7, Pin 5 Open, ÷ 4), fCUTOFF = 32kHz VS = 3V 8 9 mA mA 7 9 10 mA mA 9 13 14 mA mA 14 mA mA 30 mA mA 37 mA mA 4.6 V ● VS = 10V ● fCLK = 4.096MHz (10k from Pin 6 to Pin 7, Pin 5 Shorted to Pin 4, ÷ 1), fCUTOFF = 128kHz VS = 3V fCLK = 8.192MHz (5k from Pin 6 to Pin 7, Pin 5 Shorted to Pin 4, ÷ 1), fCUTOFF = 256kHz VS = 5V 9.5 ● 20 ● VS = 10V 27 ● Power Supply Voltage where Low Power Mode is Enabled Pin 5 Shorted to Pin 4, Note 3 ● 3.7 UNITS mV mV mV 6 ● VS = 5V MAX ±5 ±12 4.2 Clock Feedthrough REXT = 10k, Pin 5 Open 0.4 mVRMS Wideband Noise Noise BW = DC to 2 • fCUTOFF 125 µVRMS THD fIN = 10kHz, 1.5VP-P 74 dB Clock-to-Cutoff Frequency Ratio 32 Max Clock Frequency (Note 4) VS = 3V VS = 5V VS = ±5V Min Clock Frequency (Note 5) 3V to ±5V, TA < 85°C Input Frequency Range Aliased Components <–65dB Note 1: Absolute maximum ratings are those values beyond which the life of a device may be impaired. Note 2: DC offset is measured with respect to Pin 3. Note 3: There are several operating modes which reduce the supply current. For VS < 4V, the current is reduced by 50%. If the internal oscillator is used as the clock source and the divide-by-4 or divide-by-16 mode is enabled, the supply current is reduced by 60% independent of the value of VS. 5 9.6 13 MHz MHz MHz 3 kHz 0.9 • fCLK Hz Note 4: The maximum clock frequency is arbitrarily defined as the frequency at which the filter AC response exhibits >1dB of gain peaking. Note 5: The minimum clock frequency is arbitrarily defined as the frequecy at which the filter DC offset changes by more than 5mV. Note 6: Thermal resistance varies depending upon the amount of PC board metal attached to the device. θJA is specified for a 2500mm2 test board covered with 2oz copper on both sides. 3 LTC1569-7 U W TYPICAL PERFOR A CE CHARACTERISTICS Passband Gain and Group Delay vs Frequency Gain vs Frequency 10 20 VS = 3V fC = 128kHz 19 REXT = 10k PIN 5 AT V – 18 17 1 0 16 GAIN (dB) –1 15 14 –2 DELAY (µs) LOG MAG (10dB/DIV) VS = 3V fC = 128kHz REXT = 10k PIN 5 AT V – 13 12 –3 11 –90 5 10 100 FREQUENCY (kHz) –4 1000 10 FREQUENCY (kHz) 1 1569-7 G03 1569-7 G04 THD vs Input Voltage THD vs Input Frequency 12 VS = 3V PIN 3 = 1.11V –60 VS = 5V PIN 3 = 2V THD (dB) –72 –74 VIN = 1.5VP-P fCUTOFF = 128kHz IN + TO OUT REXT = 10k PIN 5 AT V – –76 10 –70 1 2 3 4 INPUT VOLTAGE (VP-P) DIV-BY-16 6 DIV-BY-4 5 5 1 10 100 fCUTOFF (kHz) ± 5V Supply Current 35 23 32 21 DIV-BY-1 19 17 DIV-BY-1 29 26 ISUPPLY (mA) EXT CLK 15 13 11 23 EXT CLK 20 17 14 9 11 DIV-BY-16 7 DIV-BY-16 DIV-BY-4 8 DIV-BY-4 5 5 1 10 100 fCUTOFF (kHz) 1000 1569-7 G06 1 1000 1569-7 G05 1569-7 G02 5V Supply Current ISUPPLY (mA) EXT CLK 7 4 0 10 20 30 40 50 60 70 80 90 100 INPUT FREQUENCY (kHz) 1569-7 G01 4 8 –90 0 DIV-BY-1 9 fIN = 10kHz fCUTOFF = 128kHz IN + TO OUT REXT = 10k PIN 5 AT V – –80 –78 11 VS = 5V PIN 3 = 2V ISUPPLY (mA) –70 THD (dB) 3V Supply Current –50 –68 10 100 10 100 fCUTOFF (kHz) 1000 1569-7 G07 LTC1569-7 U U U PIN FUNCTIONS IN +/IN – (Pins 1, 2): Signals can be applied to either or both input pins. The DC gain from IN + (Pin 1) to OUT (Pin␣ 8) is 1.0, and the DC gain from Pin 2 to Pin 8 is –1. The input range, input resistance and output range are described in the Applications Information section. Input voltages which exceed the power supply voltages should be avoided. Transients will not cause latchup if the current into/out of the input pins is limited to 20mA. DIV/CLK (Pin 5): DIV/CLK serves two functions. When the internal oscillator is enabled, DIV/CLK can be used to engage an internal divider. The internal divider is set to 1:1 when DIV/CLK is shorted to V – (Pin 4). The internal divider is set to 4:1 when DIV/CLK is allowed to float (a 100pF bypass to V – is recommended). The internal divider is set to 16:1 when DIV/CLK is shorted to V + (Pin 7). In the divide-by-4 and divide-by-16 modes the power supply current is reduced by typically 60%. GND (Pin 3): The GND pin is the reference voltage for the filter and should be externally biased to 2V (1.11V) to maximize the dynamic range of the filter in applications using a single 5V (3V) supply. For single supply operation, the GND pin should be bypassed with a quality 1µF ceramic capacitor to V – (Pin 4). The impedance of the circuit biasing the GND pin should be less than 2kΩ as the GND pin generates a small amount of AC and DC current. For dual supply operation, connect Pin␣ 3 to a high quality DC ground. A ground plane should be used. A poor ground will increase DC offset, clock feedthrough, noise and distortion. When the internal oscillator is disabled (RX shorted to V –) DIV/CLK becomes an input pin for applying an external clock signal. For proper filter operation, the clock waveform should be a squarewave with a duty cycle as close as possible to 50% and CMOS voltages levels (see Electrical Characteristics section for voltage levels). DIV/ CLK pin voltages which exceed the power supply voltages should be avoided. Transients will not cause latchup if the fault current into/out of the DIV/CLK pin is limited to 40mA. RX (Pin 6): Connecting an external resistor between the RX pin and V + (Pin 7) enables the internal oscillator. The value of the resistor determines the frequency of oscillation. The maximum recommended resistor value is 40k and the minimum is 3.8k/8k (single 5V/3V supply). The internal oscillator is disabled by shorting the RX pin to V – (Pin 4). (Please refer to the Applications Information section.) V –/V + (Pins 4, 7): For 3V, 5V and ±5V applications a quality 1µF ceramic bypass capacitor is required from V + (Pin 7) to V – (Pin 4) to provide the transient energy for the internal clock drivers. The bypass should be as close as possible to the IC. In dual supply applications (Pin 3 is grounded), an additional 0.1µF bypass from V + (Pin 7) to GND (Pin 3) and V – (Pin 4) to GND (Pin 3) is recommended. OUT (Pin 8): Filter Output. This pin can drive 10kΩ and/or 40pF loads. For larger capacitive loads, an external 100Ω series resistor is recommended. The output pin can exceed the power supply voltages by up to ±2V without latchup. The maximum voltage difference between GND (Pin 3) and V + (Pin 7) should not exceed 5.5V. W BLOCK DIAGRA IN + 1 8 OUT 10TH ORDER LINEAR PHASE FILTER NETWORK IN – 2 7 V+ REXT GND 3 V– 4 POWER CONTROL 6 RX DIVIDER/ BUFFER 5 DIV/CLK PRECISION OSCILLATOR 1569-7 BD 5 LTC1569-7 U U W U APPLICATIONS INFORMATION Self-Clocking Operation The LTC1569-7 features a unique internal oscillator which sets the filter cutoff frequency using a single external resistor. The design is optimized for VS = 3V, fCUTOFF = 128kHz, where the filter cutoff frequency error is typically <1% when a 0.1% external 10k resistor is used. With different resistor values and internal divider settings, the cutoff frequency can be accurately varied from 2kHz to 150kHz/300kHz (single 3V/5V supply). As shown in Figure 1, the divider is controlled by the DIV/CLK (Pin 5). Table 1 summarizes the cutoff frequency vs external resistor values for the divide-by-1 mode. In the divide-by-4 and divide-by-16 modes, the cutoff frequencies in Table 1 will be lowered by 4 and 16 respectively. When the LTC1569-7 is in the divide-by-4 and divide-by-16 modes the power is automatically reduced. This results in a 60% power savings with a single 5V supply. Table1. fCUTOFF vs REXT, VS = 3V, TA = 25°C, Divide-by-1 Mode REXT Typical fCUTOFF Typical Variation of fCUTOFF 3844Ω 320kHz ±3.0% 5010Ω 256kHz ±2.5% 10k 128kHz ±1% 20.18k 64kHz ±2.0% 40.2k 32kHz ±3.5% The power reduction in the divide-by-4 and divide-by-16 modes, however, effects the fundamental oscillator frequency. Hence, the effective divide ratio will be slightly different from 4:1 or 16:1 depending on VS, TA and REXT. Typically this error is less than 1% (Figures 4 and 6). 1.04 REXT = 5k REXT = 10k REXT = 20k REXT = 40k 1 2 IN + OUT IN – V+ 8 7 REXT LTC1569-7 3 4 fCUTOFF = GND V– 6 RX DIVIDE-BY-16 5 DIV/CLK 128kHz (10k/REXT) V+ DIVIDE-BY-4 100pF 0.99 0.98 2 4 6 VSUPPLY (V) 8 10 Figure 2. Filter Cutoff vs VSUPPLY, Divide-by-1 Mode, TA = 25°C 1.010 4.08 VS = 3V VS = 5V VS = 10V REXT = 5k REXT = 10k REXT = 20k REXT = 40k 1.004 DIVIDE RATIO NORMALIZED FILTER CUTOFF 1.00 1569-7 F02 Figure 1 1.006 1.01 0.96 1569-7 F01 1.008 1.02 0.97 V– DIVIDE-BY-1 1, 4 OR 16 NORMALIZED FILTER CUTOFF 1.03 1.002 1.000 0.998 4.04 4.00 0.996 0.994 0.992 0.990 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 1569-7 F03 Figure 3. Filter Cutoff vs Temperature, Divide-by-1 Mode, REXT = 10k 6 3.96 2 4 6 VSUPPLY (V) 8 10 1569-7 F04 Figure 4. Typical Divide Ratio in the Divide-by-4 Mode, TA = 25°C LTC1569-7 U W U U APPLICATIONS INFORMATION 1.010 1.006 16.32 VS = 3V VS = 5V VS = 10V REXT = 5k REXT = 10k REXT = 20k REXT = 40k 1.004 DIVIDE RATIO NORMALIZED FILTER CUTOFF 1.008 1.002 1.000 0.998 16.16 16.00 0.996 0.994 0.992 0.990 –50 –25 0 25 50 TEMPERATURE (°C) 75 15.84 100 2 1569-7 F05 4 6 VSUPPLY (V) 8 10 1569-7 F06 Figure 6. Typical Divide Ratio in the Divide-by-16 Mode, TA = 25°C Figure 5. Filter Cutoff vs Temperature, Divide-by-4 Mode, REXT = 10k 1.010 NORMALIZED FILTER CUTOFF 1.008 1.006 VS = 3V VS = 5V VS = 10V 1.004 1.002 1.000 0.998 0.996 0.994 0.992 0.990 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 1569-7 F07 Figure 7. Filter Cutoff vs Temperature, Divide-by-16 Mode, REXT = 10k The cutoff frequency is easily estimated from the equation in Figure 1. Examples 1 and 2 illustrate how to use the graphs in Figures 2 through 7 to get a more precise estimate of the cutoff frequency. Example 1: LTC1569-7, REXT = 20k, VS = 3V, divide-by-16 mode, DIV/CLK (Pin␣ 5) connected to V + (Pin 7), TA = 25°C. Using the equation in Figure 1, the approximate filter cutoff frequency is fCUTOFF = 128kHz • (10k/20k) • (1/16) = 4kHz. For a more precise fCUTOFF estimate, use Table 1 to get a value of fCUTOFF when REXT = 20k and use the graph in Figure 6 to find the correct divide ratio when VS = 3V and REXT = 20k. Based on Table 1 and Figure 6, fCUTOFF = 64kHz • (20.18k/20k) • (1/16.02) = 4.03kHz. From Table 1, the part-to-part variation of fCUTOFF will be ±2%. From the graph in Figure 7, the 0°C to 70°C drift of fCUTOFF will be – 0.2% to 0.2%. Example 2: LTC1569-7, REXT = 5k, VS = 5V, divide-by-1 mode, DIV/CLK (Pin␣ 5) connected to V – (Pin 4), TA = 25°C. Using the equation in Figure 1, the approximate filter cutoff frequency is fCUTOFF = 128kHz • (10k/5k) • (1/1) = 256kHz. For a more precise fCUTOFF estimate, use Table 1 to get fCUTOFF frequency for REXT = 5k and use Figure 2 to correct for the supply voltage when VS = 5V. From Table␣ 1 and Figure 2, fCUTOFF = 256k • (5.01k/5k) • 0.970 = 249kHz. 7 LTC1569-7 U W U U APPLICATIONS INFORMATION The oscillator is sensitive to transients on the positive supply. The IC should be soldered to the PC board and the PCB layout should include a 1µF ceramic capacitor between V + (Pin 7) and V – (Pin 4) , as close as possible to the IC to minimize inductance. Avoid parasitic capacitance on RX and avoid routing noisy signals near RX (Pin 6). Use a ground plane connected to V – (Pin 4) for single supply applications. Connect a ground plane to GND (Pin 3) for dual supply applications and connect V – (Pin 4) to a copper trace with low thermal resistance. input signal at IN + should be centered around the DC voltage at IN –. The input can also be AC coupled, as shown in the Typical Applications section. Input and Output Range Dynamic Input Impedance The input signal range includes the full power supply range. The output voltage range is typically (V – + 50mV) to (V + – 0.8V). To maximize the undistorted peak-to-peak signal swing of the filter, the GND (Pin 3) voltage should be set to 2V (1.11V) in single 5V (3V) supply applications. The unique input sampling structure of the LTC1569-7 has a dynamic input impedance which depends on the configuration, i.e., differential or single-ended, and the clock frequency. The equivalent circuit in Figure 8 illustrates the The LTC1569-7 can be driven with a single-ended or differential signal. When driven differentially, the voltage between IN + and IN – (Pin 1 and Pin 2) is filtered with a DC gain of 1. The single-ended output voltage OUT (Pin 8) is referenced to the voltage of the GND (Pin 3). The common mode voltage of IN + and IN – can be any voltage that keeps the input signals within the power supply range. For noninverting single-ended applications, connect IN – to GND or to a quiet DC reference voltage and apply the input signal to IN +. If the input is DC coupled then the DC gain from IN + to OUT will be 1. This is true given IN + and OUT are referenced to the same voltage, i.e., GND, V – or some other DC reference. To achieve the distortion levels shown in the Typical Performance Characteristics the IN – 2 i= + 125k 8 OUT 125k IN + 1 GND 3 125k – + 1569-7 F08 Figure 8 8 Refer to the Typical Performance Characteristics section to estimate the THD for a given input level. input impedance when the cutoff frequency is 128kHz. For other cutoff frequencies replace the 125k value with 125k • (128kHz/fCUTOFF). When driven with a single-ended signal into IN – with IN + tied to GND, the input impedance is very high (~10MΩ). When driven with a single-ended signal into IN + with IN – tied to GND, the input impedance is a 125k resistor to GND. When driven with a complementary signal whose common mode voltage is GND, the IN+ input appears to have 125k to GND and the IN – input appears to have –125k to GND. To make the effective IN – impedance 125k when driven differentially, place a 62.5k resistor from IN – to GND. For other cutoff frequencies use 62.5k • (128kHz/ fCUTOFF), as shown in the Typical Applications section. The typical variation in dynamic input impedance for a given clock frequency is ±10%. Wideband Noise – IN + – GND For inverting single-ended filtering, connect IN+ to GND or to quiet DC reference voltage. Apply the signal to IN –. The DC gain from IN – to OUT is –1, assuming IN – is referenced to IN + and OUT is reference to GND. The wideband noise of the filter is the RMS value of the device’s output noise spectral density. The wideband noise data is used to determine the operating signal-tonoise at a given distortion level. The wideband noise is nearly independent of the value of the clock frequency and excludes the clock feedthrough. Most of the wideband noise is concentrated in the filter passband and cannot be removed with post filtering (Table 2). Table 3 lists the typical wideband noise for each supply. LTC1569-7 U W U U APPLICATIONS INFORMATION Bandwidth Total Integrated Noise DC to fCUTOFF 105µVRMS DC to 2 • fCUTOFF 125µVRMS DC to fCLK 155µVRMS 12-bit DC accuracy. Figure 9 illustrates the typical DC accuracy of the LTC1569-7 on a single 5V supply. 488 244 DC ERROR (µV) Table 2. Wideband Noise vs Supply Voltage, Single 3V Supply Table 3. Wideband Noise vs Supply Voltage, fCUTOFF = 128kHz Power Supply Total Integrated Noise DC to 2 • fCUTOFF 3V 125µVRMS 5V 135µVRMS ±5V 145µVRMS 000 –244 VS = 5V REXT = 10k TA = 25°C –488 –1.5 Clock Feedthrough –1.0 –0.5 0 0.5 VIN DC (V) 1.0 1.5 1569-7 F09 Clock feedthrough is defined as the RMS value of the clock frequency and its harmonics that are present at the filter’s OUT pin (Pin 8). The clock feedthrough is measured with IN + and IN – (Pins 1 and 2) grounded and depends on the PC board layout and the power supply decoupling. Table␣ 4 shows the clock feedthrough (the RMS sum of the first 11 harmonics) when the LTC1569-7 is self-clocked with REXT = 10k, DIV/CLK (Pin 5) open (divide-by-4 mode). The clock feedthrough can be reduced with a simple RC post filter. Table 4. Clock Feedthrough Power Supply Feedthrough 3V 0.4mVRMS 5V 0.6mVRMS ±5V 0.9mVRMS DC Accuracy DC accuracy is defined as the error in the output voltage after DC offset and DC gain errors are removed. This is similar to the definition of the integral nonlinearity in A/D converters. For example, after measuring values of VOUT(DC) vs VIN(DC) for a typical LTC1569-7, a linear regression shows that VOUT(DC) = VIN(DC) • 0.99854 + 0.00134V is the straight line that best fits the data. The DC accuracy describes how much the actual data deviates from this straight line (i.e., DCERROR = VOUT(DC) – (VIN(DC) • 0.99854 + 0.00134V). In a 12-bit system with a full-scale value of 2V, the LSB is 488µV. Therefore, if the DCERROR of the filter is less than 488µV over a 2V range, the filter has Figure 9 DC Offset The output DC offset of the LTC1569-7 is trimmed to less than ±5mV. The trimming is performed with VS = 1.9V, –1.1V with the filter cutoff frequency set to 8kHz (REXT = 10k, DIV/CLK shorted to V +). To obtain optimum DC offset performance, appropriate PC layout techniques should be used. The filter IC should be soldered to the PC board. The power supplies should be well decoupled including a 1µF ceramic capacitor from V + (Pin 7) to V – (Pin 4). A ground plane should be used. Noisy signals should be isolated from the filter input pins. When the power supply is 3V, the output DC offset should not change more than ±2mV when the clock frequency varies from 64kHz to 8192kHz. When the clock frequency is fixed, the output DC offset will typically change by ±3mV (±15mV) when the power supply varies from 3V to 5V (±5V) in the divide-by-1 mode. In the divide-by-4 or divide-by-16 modes, the output DC offset will typically change – 9mV (– 27mV) when the power supply varies from 3V to 5V (±5V). The offset is measured with respect to GND (Pin 3). Aliasing Aliasing is an inherent phenomenon of sampled data filters. In lowpass filters significant aliasing only occurs when the frequency of the input signal approaches the sampling frequency or multiples of the sampling frequency. The LTC1569-7 samples the input signal twice 9 LTC1569-7 U U W U APPLICATIONS INFORMATION every clock period. Therefore, the sampling frequency is twice the clock frequency and 64 times the filter cutoff frequency. Input signals with frequencies near 2 • fCLK ± fCUTOFF will be aliased to the passband of the filter and appear at the output unattenuated. Power Supply Current The power supply current depends on the operating mode. When the LTC1569-7 is in the divide-by-1 mode, or when clocked externally, the supply current is reduced by 50% for supply voltages below 4V. For the divide-by-4 and divide-by-16 modes, the supply current is reduced by 60% relative to the current when clocked externally, independent of the power supply voltage. Power supply current versus cutoff frequency for various operating modes is shown in the “Typical Performance Characteristics” section. U TYPICAL APPLICATIO S Single 3V, AC Coupled Input, 128kHz Cutoff Frequency Single 3V Operation, AC Coupled Input, 128kHz Cutoff Frequency 1 3V 2 IN + IN – 14µs REXT = 10k 7 V+ 16µs VOUT 3V GND 6 RX 1µF 4 fCUTOFF = V – 5 DIV/CLK 0 –10 GAIN (dB) 3 0 1µF LTC1569-7 3.48k 2k 8 OUT 20k 40k 12µs 80k 100k 120k 140k 60k GROUP DELAY 0.1µF VIN –20 –30 –40 –50 1569-7 TA02 ( )( ) –60 128kHz 10k –70 n=1 REXT –80 n = 1, 4, 16 FOR PIN 5 AT GROUND, OPEN, V + –90 0 80k 100k 120k 140k 160k 180k 200k 220k 240k 260k 280k 300k FREQUENCY (Hz) 1569-7 TA02a Single 3V Supply Operation, DC Coupled, 32kHz Cutoff Frequency VIN 1 IN + 3V 2 V+ 8 7 3 REXT = 10k GND RX 5V 3V 1µF 6 fCUTOFF = V– DIV/CLK 5 ( )( ) 128kHz 10k n=4 REXT n = 1, 4, 16 FOR PIN 5 AT GROUND, OPEN, V + IN LT®1460-2.5 OUT (SOT-23) GND 1µF 4 10 VOUT LTC1569-7 3.48k 2k IN – OUT Single 5V Operation, 300kHz Cutoff Frequency, DC Coupled Differential Inputs with Balanced Input Impedance VIN + 1 IN + OUT VIN – 2 IN – V+ 7 3 GND RX VOUT REXT = 4.1k 5V 1µF LTC1569-7 27k 6 1µF 4 100pF 1569-7 TA04 8 fCUTOFF ~ V– DIV/CLK 5 ( )( ) 128kHz 10k n=1 4.1k n = 1, 4, 16 FOR PIN 5 AT GROUND, OPEN, V + 1569-7 TA03 LTC1569-7 U TYPICAL APPLICATION Dual 5V Supply Operation, DC Coupled Filter with External Clock Source VIN 1 2 IN + OUT IN – V+ 8 VOUT fCUTOFF = fCLK/32 7 GND RX VIN 5V 5V 0.1µF LTC1569-7 3 Single 5V Supply Operation, DC Coupled Input, 128kHz Cutoff Frequency V– DIV/CLK OUT 2 IN – V+ 6 3 5 8 7 VOUT REXT = 10k GND 5V 1µF LTC1569-7 RX 6 1µF 1.65k 4 IN + 2.49k 0.1µF –5V 1 5V 0V fCLK ≤ 10MHz 4 1569-7 TA05 fCUTOFF = 1µF V– DIV/CLK 5 ( )( ) 128kHz 10k n=1 REXT 1569-7 TA06 n = 1, 4, 16 FOR PIN 5 AT GROUND, OPEN, V + U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) TYP *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 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. SO8 0996 11 LTC1569-7 U TYPICAL APPLICATIO S Pulse Shaping Circuit for Single 3V Operation, 300kbps 2 level data, 150kHz Cutoff Filter Pulse Shaping Circuit for Single 3V Operation, 400kbps (200ksps) 4 Level Data, 128kHz Cutoff Filter +3V +3V 200ksps DATA 20k 4.99k 4.99k 1 20k +3V 300kbps DATA 2 IN + IN – 3.48k OUT V+ 8 7 VOUT REXT = 8.56k 1µF 4 2k GND RX 1 +3V 10k +3V D0 1µF LTC1569-7 3 20k D1 6 DIV/CLK 2k V+ 8 7 VOUT REXT = 8.56k 1µF 4 GND V– RX 1µF DIV/CLK 6 5 1569-7 TA09 1569-7 TA10 4-Level, 400kbps (200ksps) Eye Diagram 2-Level, 300kbps Eye Diagram 0.3V/DIV 0.25V/DIV +3V LTC1569-7 3 5 OUT IN – 3.48k 20k V– 2 IN + 1µs/DIV 1µs/DIV 1569-7 TA07 1569-7 TA08 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1064-3 Linear Phase, Bessel 8th Order Filter fCLK/fCUTOFF = 75/1 or 150/1, Very Low Noise LTC1064-7 Linear Phase, 8th Order Lowpass Filter fCLK/fCUTOFF = 50/1 or 100/1, fCUTOFF(MAX) = 100kHz LTC1068-x Universal, 8th Order Filter fCLK/fCUTOFF = 25/1, 50/1, 100/1 or 200/1, fCUTOFF(MAX) = 200kHz LTC1069-7 Linear Phase, 8th Order Lowpass Filter fCLK/fCUTOFF = 25/1, fCUTOFF(MAX) = 200kHz, SO-8 LTC1164-7 Low Power, Linear Phase Lowpass Filter fCLK/fCUTOFF = 50/1 or 100/1, IS = 2.5mA, VS = 5V LTC1264-7 Linear Phase, 8th Order Lowpass Filter fCLK/fCUTOFF = 25/1 or 50/1, fCUTOFF(MAX) = 200kHz LTC1562/LTC1562-2 Universal, 8th Order Active RC Filter fCUTOFF(MAX) = 150kHz (LTC1562) fCUTOFF(MAX) = 300kHz (LTC1562-2) 12 Linear Technology Corporation 15697f LT/TP 0300 4K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1998