Datasheet LTC1569-7 Datasheet (Linear Technology)

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Page 1

LTC1569-7

Linear Phase, DC Accurate,

Tunable, 10th Order Lowpass Filter

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, V

■

Low Power Modes

■

Differential or Single-Ended Inputs

■

80dB CMRR (DC)

■

80dB Signal-to-Noise Ratio, VS = 5V

■

Operates from 3V to ±5V Supplies

OS(MAX)

= 5mV

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

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.

Furthermore, its root raised cosine response offers the optimum pulse shaping for PAM data communications

The filter attenuation is 50dB at 1.5 • f f

, and in excess of 80dB at 6 • f

CUTOFF

, 60dB at 2 •

CUTOFF

. DC-accuracy-

sensitive applications benefit from the 5mV maximum DC offset.

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.

TYPICAL APPLICATION

Single 3V Supply, 128kHz/32kHz/8kHz Lowpass Filter

OUTV

3.48k

–

LTC1569-7

GND

1µF

–

DIV/CLK

EASY TO SET f

CUTOFF

128kHz (10k/R

1, 4 OR 16

OUT

= 10k

EXT

1/16

1/4

1/1

)

EXT

1µF

100pF

1569-7 TA01

Frequency Response, f

–20

–40

GAIN (dB)

–60

–80

–100

10 100 1000 FREQUENCY (kHz)

= 128kHz/32kHz/8kHz

CUTOFF

1569-7 TA01a

Page 2

LTC1569-7

TOP VIEW

OUT V

DIV/CLK

–

GND

–

S8 PACKAGE

8-LEAD PLASTIC SO

LUTEXI TIS

WUW

ARB

PACKAGE

RDER I FOR ATIO

(Note 1)

Total Supply Voltage................................................ 11V

Power Dissipation.............................................. 500mW

Operating Temperature

LTC1569C ............................................... 0°C to 70°C

ORDER PART

NUMBER

LTC1569CS8-7 LTC1569IS8-7

LTC1569I............................................ –40°C to 85°C

Storage Temperature ............................ –65°C to 150°C

Lead Temperature (Soldering, 10 sec)..................300°C

= 125°C, θJA = 80°C/W (Note 6)

JMAX

S8 PART

MARKING

15697 1569I7

Consult factory for Military grade parts.

LECTRICAL C CHARA TERIST

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), f

PARAMETER CONDITIONS MIN TYP MAX UNITS

Filter Gain VS = 5V, f

CUTOFF

= 5k, Pin 5 Shorted to Pin 4 fIN = 128kHz = 0.5 • f

EXT

VS = 2.7V, f f

CUTOFF

Pin 6 Shorted to Pin 4, External Clock f

Filter Phase VS = 2.7V, f

CUTOFF

Pin 4, External Clock f

Filter Cutoff Accuracy R when Self-Clocked V

Filter Output DC Swing VS = 3V, Pin 3 = 1.11V 2.1 V

= 10.24k from Pin 6 to Pin 7, 125kHz ±1%

EXT

= 3V, Pin 5 Shorted to Pin 4

VS = 5V, Pin 3 = 2V 3.9 V

VS = ±5V 8.6 V

= 128kHz, R

CUTOFF

= 8.192MHz, fIN = 5120Hz = 0.02 • f

CLK

= 256kHz, VIN = 2.5V

= 1MHz, fIN = 625Hz = 0.02 • f

CLK

= 31.25kHz, VIN = 1V

= 4MHz, fIN = 2500Hz = 0.02 • f

CLK

= 125kHz, Pin 6 Shorted to fIN = 25kHz = 0.2 • f

ICS

= 10k unless otherwise specified.

LOAD

P-P

= 51.2kHz = 0.2 • f

= 204.8kHz = 0.8 • f

= 256kHz = f

= 384kHz = 1.5 • f

= 512kHz = 2 • f

= 768kHz = 3 • f

= 6.25kHz = 0.2 • f

= 15.625kHz = 0.5 • f

= 25kHz = 0.8 • f

= 31.25kHz = f

= 46.875kHz = 1.5 • f

= 62.5kHz = 2 • f

= 93.75kHz = 3 • f

= 62.5kHz = 0.5 • f

= 100kHz = 0.8 • f

= 125kHz = f

= 187.5kHz = 1.5 • f

LTC1569C ● 8.4 V LTC1569I ● 8.0 V

CUTOFF

, LTC1569C ● –5.7 –3.8 –2.3 dB

CUTOFF

, LTC1569I ● –6.2 –3.8 –2.0 dB

CUTOFF

CUTOFF CUTOFF CUTOFF

CUTOFF

● –0.10 0.00 0.10 dB

● –0.25 –0.15 –0.05 dB

● –0.50 –0.41 –0.25 dB

● –1.1 –0.65 –0.40 dB

● –58 –48 dB

● –62 –54 dB

● –67 –64 dB

● –0.08 0.00 0.12 dB

● –0.25 –0.15 –0.05 dB

● –0.50 –0.40 –0.30 dB

● –0.75 –0.65 –0.50 dB

● –3.3 –3.15 –3.0 dB

● –57 –52 dB

● –60 –54 dB

● –66 –58 dB

–11 Deg

● –114 –112 –110 Deg

● 78 80 82 Deg

● –85 –83 –81 Deg

● 155 158 161 Deg

–95 Deg

● 1.9 V

● 3.7 V

P-P P-P

P-P

Page 3

LTC1569-7

LECTRICAL C CHARA TERIST

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), f

PARAMETER CONDITIONS MIN TYP MAX UNITS

Output DC Offset R (Note 2) V

Output DC Offset Drift R

Clock Pin Logic Thresholds VS = 3V Min Logical “1” 2.6 V when Clocked Externally Max Logical “0” 0.5 V

Power Supply Current f (Note 3) Pin 5 Open, ÷ 4), f

Power Supply Voltage where Pin 5 Shorted to Pin 4, Note 3 ● 3.7 4.2 4.6 V Low Power Mode is Enabled

Clock Feedthrough R Wideband Noise Noise BW = DC to 2 • f THD fIN = 10kHz, 1.5V Clock-to-Cutoff 32

Frequency Ratio Max Clock Frequency VS = 3V 5 MHz

(Note 4) V

Min Clock Frequency 3V to ±5V, TA < 85°C3kHz (Note 5)

Input Frequency Range Aliased Components <–65dB 0.9 • f

= 4.096MHz, f

CLK

= 10k, Pin 5 Shorted to Pin 4 VS = 3V ±2 ±5mV

EXT

= 10k, Pin 5 Shorted to Pin 4 VS = 3V –25 µV/°C

EXT

VS = 5V Min Logical “1” 4.0 V

VS = ±5V Min Logical “1” 4.0 V

= 1.028MHz (10k from Pin 6 to Pin 7, VS = 3V 6 8 mA

CLK

= 4.096MHz (10k from Pin 6 to Pin 7, VS = 3V 9.5 mA

CLK

Pin 5 Shorted to Pin 4, ÷ 1), f f

= 8.192MHz (5k from Pin 6 to Pin 7, VS = 5V 20 mA

CLK

Pin 5 Shorted to Pin 4, ÷ 1), f

= 10k, Pin 5 Open 0.4 mV

EXT

P-P

= 5V 9.6 MHz

= ±5V 13 MHz

ICS

= 128kHz, R

CUTOFF

= 32kHz ● 9mA

CUTOFF

= 128kHz ● 14 mA

CUTOFF

= 256kHz ● 30 mA

CUTOFF

= 10k unless otherwise specified.

LOAD

= 5V ±6 ±12 mV

= ±5V ±15 mV

= 5V –25 µV/°C

= ±5V ±25 µV/°C

Max Logical “0” 0.5 V

VS = 5V 7 9 mA

VS = 10V 9 13 mA

VS = 10V 27 mA

● 10 mA

● 14 mA

● 37 mA

125 µV

74 dB

CLK

RMS

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 V 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 V

< 4V, the current is reduced by 50%. If the internal

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. θ covered with 2oz copper on both sides.

is specified for a 2500mm2 test board

Page 4

LTC1569-7

FREQUENCY (kHz)

GAIN (dB)

DELAY (µs)

–1

–2

–3

–4

20 19 18 17 16 15 14 13 12 11 10

10 100

1569-7 G04

VS = 3V f

= 128kHz

EXT

= 10k

PIN 5 AT V

–

TYPICAL PERFOR A CE CHARACTERISTICS

Gain vs Frequency

LOG MAG (10dB/DIV)

–90

10 100 1000

FREQUENCY (kHz)

VS = 3V f

= 128kHz

= 10k

EXT

PIN 5 AT V

1569-7 G03

–

Passband Gain and Group Delay vs Frequency

–68

–70

–72

THD (dB)

–74

–76

–78

THD vs Input Frequency

VS = 5V PIN 3 = 2V

VIN = 1.5V

P-P

= 128kHz

CUTOFF

TO OUT

= 10k

EXT

PIN 5 AT V

10 30 50 70 9040 60 80 100

020

INPUT FREQUENCY (kHz)

–

5V Supply Current

(mA)

SUPPLY

DIV-BY-16

10 100 1000

CUTOFF

1569-7 G01

DIV-BY-1

DIV-BY-4

(kHz)

EXT CLK

1569-7 G06

THD vs Input Voltage

–50

VS = 3V PIN 3 = 1.11V

–60

–70

THD (dB)

–80

–90

1 2 3 45

VS = 5V PIN 3 = 2V

fIN = 10kHz f

CUTOFF

IN R PIN 5 AT V

INPUT VOLTAGE (V

TO OUT

EXT

P-P

= 128kHz

= 10k

)

(mA)

SUPPLY

(mA)

SUPPLY

–

1569-7 G02

5V Supply Current

35 32 29 26 23 20 17 14 11

DIV-BY-16

10 100 1000

3V Supply Current

DIV-BY-16

CUTOFF

10 100 1000

DIV-BY-1

EXT CLK

DIV-BY-4

(kHz)

CUTOFF

1569-7 G07

DIV-BY-1

EXT CLK

DIV-BY-4

(kHz)

1569-7 G05

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PIN FUNCTIONS

LTC1569-7

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.

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.

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.

The maximum voltage difference between GND (Pin 3) and V+ (Pin 7) should not exceed 5.5V.

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%.

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 R

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.)

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.

BLOCK DIAGRA

1 OUT

–

GND

–

10TH ORDER

LINEAR PHASE

FILTER NETWORK

POWER

CONTROL

DIVIDER/

BUFFER

PRECISION

OSCILLATOR

DIV/CLK

1569-7 BD

EXT

Page 6

LTC1569-7

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APPLICATIONS INFORMATION

Self-Clocking Operation

The LTC1569-7 features a unique internal oscillator which sets the filter cutoff frequency using a single external resistor

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

. The design is optimized for VS = 3V, f

OUT

–

LTC1569-7

GND

–

128kHz (10k/R

CUTOFF

1.010

1.008

1.006

1.004

1.002

1.000

0.998

0.996

NORMALIZED FILTER CUTOFF

0.994

0.992

0.990 –50

Figure 3. Filter Cutoff vs Temperature, Divide-by-1 Mode, R

DIV/CLK

1, 4 OR 16

VS = 3V

= 5V

= 10V

–25

EXT

)

EXT

DIVIDE-BY-16

DIVIDE-BY-4

100pF

DIVIDE-BY-1

Figure 1

0 25 50 75 100

TEMPERATURE (°C)

= 10k

EXT

1569-7 F01

1569-7 F03

CUTOFF

–

reduced. This results in a 60% power savings with a single 5V supply.

Table1. f

EXT

3844Ω 320kHz ±3.0% 5010Ω 256kHz ±2.5% 10k 128kHz ±1%

20.18k 64kHz ±2.0%

40.2k 32kHz ±3.5%

CUTOFF

vs R

Typical f

, VS = 3V, TA = 25°C, Divide-by-1 Mode

EXT

CUTOFF

Typical Variation of f

CUTOFF

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 R

EXT

Typically this error is less than 1% (Figures 4 and 6).

1.04 R

= 5k

1.03

1.02

1.01

1.00

0.99

0.98

NORMALIZED FILTER CUTOFF

0.97

0.96

Figure 2. Filter Cutoff vs V Divide-by-1 Mode, TA = 25°C

4.08

4.04

DIVIDE RATIO

4.00

3.96

Figure 4. Typical Divide Ratio in the Divide-by-4 Mode, TA = 25°C

EXT

= 10k

EXT

= 20k

EXT

= 40k

EXT

4 6 810

(V)

SUPPLY

= 5k

EXT

= 10k

EXT

= 20k

EXT

= 40k

EXT

4 6 810

(V)

SUPPLY

1569-7 F02

1569-7 F04

Page 7

LTC1569-7

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APPLICATIONS INFORMATION

1.010

–50

VS = 3V

= 5V

= 10V

–25

0 25 50 75 100

TEMPERATURE (°C)

= 10k

EXT

1569-7 F05

1.010

1.008

1.006

1.004

1.002

1.000

0.998

0.996

NORMALIZED FILTER CUTOFF

0.994

0.992

0.990 –50

Figure 7. Filter Cutoff vs Temperature, Divide-by-16 Mode, R

1.008

1.006

1.004

1.002

1.000

0.998

0.996

NORMALIZED FILTER CUTOFF

0.994

0.992

0.990

Figure 5. Filter Cutoff vs Temperature, Divide-by-4 Mode, R

VS = 3V

= 5V

= 10V

–25

0 25 50 75 100

TEMPERATURE (°C)

= 10k

EXT

16.32 R

= 5k

EXT

= 10k

EXT

= 20k

EXT

= 40k

16.16

DIVIDE RATIO

16.00

15.84

EXT

4 6 810

(V)

SUPPLY

Figure 6. Typical Divide Ratio in the Divide-by-16 Mode, TA = 25°C

1569-7 F07

1569-7 F06

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, R

= 20k, VS = 3V, divide-by-16

EXT

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 f

= 128kHz • (10k/20k)

CUTOFF

• (1/16) = 4kHz. For a more precise f

a value of f

CUTOFF

when R

estimate, use Table 1 to get

CUTOFF

= 20k and use the graph

EXT

in Figure 6 to find the correct divide ratio when VS = 3V and R

= 20k. Based on Table 1 and Figure 6, f

EXT

CUTOFF

= 64kHz • (20.18k/20k) • (1/16.02) = 4.03kHz.

From Table 1, the part-to-part variation of f

CUTOFF

will

be ±2%. From the graph in Figure 7, the 0°C to 70°C drift of f

Example 2: LTC1569-7, R

will be –0.2% to 0.2%.

CUTOFF

EXT

= 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 f

= 128kHz • (10k/5k)

CUTOFF

• (1/1) = 256kHz. For a more precise f

frequency for R

CUTOFF

estimate, use Table 1 to get

CUTOFF

= 5k and use Figure 2 to

EXT

correct for the supply voltage when VS = 5V. From Table␣ 1 and Figure 2, f

= 256k • (5.01k/5k) •

CUTOFF

0.970 = 249kHz.

Page 8

LTC1569-7

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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 be- tween 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 and Output Range

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 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

–

– GND

i =

125k

GND

125k

–

125k

1569-7 F08

Figure 8

–

OUT

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.

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.

Refer to the Typical Performance Characteristics section to estimate the THD for a given input level.

Dynamic Input Impedance

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

input impedance when the cutoff frequency is 128kHz. For other cutoff frequencies replace the 125k value with 125k • (128kHz/f

When driven with a single-ended signal into IN– with IN

CUTOFF

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/ f

), as shown in the Typical Applications section. The

CUTOFF

typical variation in dynamic input impedance for a given clock frequency is ±10%.

Wideband Noise

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.

Page 9

LTC1569-7

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APPLICATIONS INFORMATION

Table 2. Wideband Noise vs Supply Voltage, Single 3V Supply

Bandwidth Total Integrated Noise

DC to f

CUTOFF

DC to 2 • f DC to f

Table 3. Wideband Noise vs Supply Voltage, f

Power Supply DC to 2 • f

3V 125µV 5V 135µV ±5V 145µV

CUTOFF

CLK

Clock Feedthrough

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 R

= 10k, DIV/CLK (Pin 5) open (divide-by-4 mode). The

EXT

clock feedthrough can be reduced with a simple RC post filter.

Table 4. Clock Feedthrough

Power Supply Feedthrough

3V 0.4mV 5V 0.6mV ±5V 0.9mV

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 V vs V shows that V

for a typical LTC1569-7, a linear regression

IN(DC)

OUT(DC)

= V

• 0.99854 + 0.00134V is the

IN(DC)

straight line that best fits the data. The DC accuracy describes how much the actual data deviates from this straight line (i.e., DCERROR = V

OUT(DC)

+ 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

105µV

RMS

125µV

RMS

155µV

RMS

= 128kHz

CUTOFF

Total Integrated Noise

CUTOFF

RMS

OUT(DC)

– (V

IN(DC)

• 0.99854

12-bit DC accuracy. Figure 9 illustrates the typical DC accuracy of the LTC1569-7 on a single 5V supply.

488

244

000

DC ERROR (µV)

–244

VS = 5V

= 10k

EXT

= 25°C

–488

–1.5 –1.0 –0.5 0 0.5 1.0 1.5

VIN DC (V)

1569-7 F09

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 (R

EXT

= 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

Page 10

LTC1569-7

WUU

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 • f ± f

will be aliased to the passband of the filter and

CUTOFF

CLK

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

TYPICAL APPLICATIO S

Single 3V Operation, AC Coupled Input,

128kHz Cutoff Frequency

0.1µF

3.48k

CUTOFF

1µF

–

LTC1569-7

GND

–

DIV/CLK

128kHz

()

n = 1

n = 1, 4, 16 FOR PIN 5 AT

GROUND, OPEN, V

OUT

10k

EXT

OUT

= 10k

EXT

1569-7 TA02

1µF

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.

Single 3V, AC Coupled Input,

128kHz Cutoff Frequency

16µs 14µs

1569-7 TA02a

12µs

140k0 20k 80k 100k40k 60k 120k

0 –10 –20 –30

GAIN (dB)

–40 –50 –60 –70 –80 –90

80k 100k 160k 180k 240k 260k120k 140k 200k 220k 280k

0 300k

FREQUENCY (Hz)

GROUP DELAY

Single 3V Supply Operation, DC Coupled,

32kHz Cutoff Frequency

3.48k

1µF

CUTOFF

–

LTC1569-7

GND

–

DIV/CLK

128kHz

()

n = 4

n = 1, 4, 16 FOR PIN 5 AT

GROUND, OPEN, V

OUT

10k

EXT

OUT

= 10k

EXT

100pF

1µF

1569-7 TA04

Single 5V Operation, 300kHz Cutoff Frequency,

DC Coupled Differential Inputs with Balanced Input Impedance

1460-2.5

GND

(SOT-23)

OUT

–

LTC1569-7

27k

GND

1µF

–

DIV/CLK

128kHz

CUTOFF

()

n = 1

4.1k

n = 1, 4, 16 FOR PIN 5 AT

GROUND, OPEN, V

OUT

10k

OUT

EXT

= 4.1k

1µF

1569-7 TA03

Page 11

TYPICAL APPLICATION

LTC1569-7

Dual 5V Supply Operation,

DC Coupled Filter with External Clock Source

0.1µF

–5V

–

LTC1569-7

GND

–

DIV/CLK

1µF

OUT

CUTOFF

PACKAGE DESCRIPTION

Single 5V Supply Operation, DC Coupled Input,

128kHz Cutoff Frequency

= f

CLK

/32

0.1µF

≤ 10MHz

1569-7 TA05

5V 0V

2.49k

1.65k

CUTOFF

GND

1µF

128kHz

()

n = 1

n = 1, 4, 16 FOR PIN 5 AT

GROUND, OPEN, V

OUT

–

LTC1569-7

–

DIV/CLK

10k

()

EXT

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)

OUT

= 10k

EXT

1µF

1569-7 TA06

0.228 – 0.244

(5.791 – 6.197)

0.010 – 0.020

(0.254 – 0.508)

0.008 – 0.010

(0.203 – 0.254)

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.

× 45°

0°– 8° TYP

0.016 – 0.050

0.406 – 1.270

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

0.150 – 0.157** (3.810 – 3.988)

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270)

TYP

SO8 0996

Page 12

LTC1569-7

TYPICAL APPLICATIO S

Pulse Shaping Circuit for Single 3V Operation, 300kbps

2 level data, 150kHz Cutoff Filter

+3V

20k

300kbps

DATA

4.99k

20k

+3V

3.48k

–

LTC1569-7

GND

1µF

–

DIV/CLK

OUT

EXT

2-Level, 300kbps Eye Diagram

OUT

= 8.56k

+3V 1µF

1569-7 TA09

Pulse Shaping Circuit for Single 3V Operation, 400kbps

(200ksps) 4 Level Data, 128kHz Cutoff Filter

200ksps

DATA

4.99k

10k

+3V

20k

+3V

3.48k

OUT

–

LTC1569-7

GND

1µF

–

DIV/CLK

4-Level, 400kbps (200ksps)

Eye Diagram

EXT

OUT

= 8.56k

+3V 1µF

1569-7 TA10

0.25V/DIV

1µs/DIV

1569-7 TA07

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LTC1064-3 Linear Phase, Bessel 8th Order Filter f LTC1064-7 Linear Phase, 8th Order Lowpass Filter f LTC1068-x Universal, 8th Order Filter f LTC1069-7 Linear Phase, 8th Order Lowpass Filter f LTC1164-7 Low Power, Linear Phase Lowpass Filter f LTC1264-7 Linear Phase, 8th Order Lowpass Filter f LTC1562/LTC1562-2 Universal, 8th Order Active RC Filter f

CLK/fCUTOFF

CUTOFF(MAX)

0.3V/DIV

1µs/DIV

1569-7 TA08

= 75/1 or 150/1, Very Low Noise = 50/1 or 100/1, f

CUTOFF(MAX)

= 25/1, 50/1, 100/1 or 200/1, f = 25/1, f

CUTOFF(MAX)

= 100kHz

CUTOFF(MAX)

= 200kHz, SO-8 = 50/1 or 100/1, IS = 2.5mA, VS = 5V = 25/1 or 50/1, f

CUTOFF(MAX)

= 200kHz

= 150kHz (LTC1562) = 300kHz (LTC1562-2)

= 200kHz

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

●

www.linear-tech.com

15697f LT/TP 0300 4K • PRINTED IN THE USA

 LINEAR TECHNOLOGY CORPORATION 1998