LTC1594LCS datasheet(21/24 Pages) LINER

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LTC1594L/LTC1598L

TYPICAL APPLICATIONS N

MULTICHANNEL A/D USES A SINGLE

ANTIALIASING FILTER

This circuit demonstrates how the LTC1598L’s indepen-

dent analog multiplexer can simplify design of a 12-bit

data acquisition system. All eight channels are MUXed into

a single 1kHz, 4th order Sallen-Key antialiasing filter,

which is designed for single supply operation. Since the

LTC1598L’s data converter accepts inputs from ground to

the positive supply, rail-to-rail op amps were chosen for

the filter to maximize dynamic range. The LT1368 dual rail-

to-rail op amp is designed to operate with 0.1

µF load

capacitors (C1 and C2). These capacitors provide fre-

quency compensation for the amplifiers and help reduce

the amplifier’s output impedance and improve supply

rejection at high frequencies. The filter contributes less

than 1LSB of error due to offsets and bias currents. The

filter’s noise and distortion are less than –72dB for a

100Hz, 2VP-P offset sine input.

The combined MUX and A/D errors result in an integral

nonlinearity error of

±3LSB (maximum) and a differential

nonlinearity error of

±3/4LSB (maximum). The typical

signal-to-noise plus distortion ratio is 68dB, with approxi-

mately –78dB of total harmonic distortion. The LTC1598L

is programmed through a 4-wire serial interface that is

compatible with MICROWIRE, SPI and QSPI. Maximum

serial clock speed is 200kHz, which corresponds to a

10.5kHz sampling rate.

The complete circuit consumes approximately 600

µA

from a single 3V supply.

Simple Data Acquisition System Takes Advantage of the LTC1598L’s

MUXOUT/ADCIN Pins to Filter Analog Signals Prior to A/D Conversion

1594L/98L TA05

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

–

8-CHANNEL

MUX

COM

GND

4, 9

5, 14

CSADC

CSMUX

CLK

DIN

DOUT

12-BIT

SAMPLING

ADC

SERIAL DATA LINK

MICROWIRE AND SPI

COMPATIBLE

ADCIN

MUXOUT

3.3V

15, 19

µF

VREF VCC

LTC1598L

0.1

µF

–

0.015

µF

0.01

µF

7.5k

0.03

µF

0.1

µF

0.015

µF

0.03

µF

1/2 LT1368

–

1/2 LT1368

LTC1594LCS Datasheet(PDF) 21 Page - Linear Technology

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