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LTC1569-7

TYPICAL APPLICATION

DESCRIPTIO

APPLICATIO S

FEATURES

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One External R Sets Cutoff Frequency

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Root Raised Cosine Response

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Up to 300kHz Cutoff on a Single 5V Supply

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Up to 150kHz Cutoff on a Single 3V Supply

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10th Order, Linear Phase Filter in an SO-8

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DC Accurate, VOS(MAX) = 5mV

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Low Power Modes

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Differential or Single-Ended Inputs

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80dB CMRR (DC)

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

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Operates from 3V to

±5V Supplies

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.

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Data Communication Filters for 3V Operation

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Linear Phase and Phase Matched Filters for I/Q

Signal Processing

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Pin Programmable Cutoff Frequency Lowpass Filters

Furthermore, its root raised cosine response offers the

optimum pulse shaping for PAM data communications.

The filter attenuation is 57dB at 1.5 • fCUTOFF, 60dB at 2 •

fCUTOFF, and in excess of 80dB at 6 • fCUTOFF. 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 fre-

quency 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.

Frequency Response, fCUTOFF = 128kHz/32kHz/8kHz

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

Linear Phase, DC Accurate,

Tunable, 10th Order Lowpass Filter

FREQUENCY (kHz)

1

0

–20

–40

–60

–80

–100

10

100

1000

1569-7 TA01a

18

27

36

45

1

µF

3V

1/4

1/16

1/1

3V

REXT = 10k

100pF

1

µF

2k

3.48k

3V

LTC1569-7

EASY TO SET fCUTOFF:

fCUTOFF =

128kHz (10k/REXT)

1, 4 OR 16

1569-7 TA01

IN+

IN–

GND

V–

OUT

VIN

VOUT

V+

RX

DIV/CLK