Datasheet

21
LTC1594/LTC1598
15948fb
TYPICAL APPLICATIONS N
U
MULTICHANNEL A/D USES A SINGLE ANTIALIASING
FILTER
This circuit demonstrates how the LTC1598’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
LTC1598’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 0.1μF 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, 2V
P-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 71dB, with approxi-
mately –78dB of total harmonic distortion. The LTC1598
is programmed through a 4-wire serial interface that is
compatable with MICROWIRE, SPI and QSPI. Maximum
serial clock speed is 320kHz, which corresponds to a
16.8kHz sampling rate.
The complete circuit consumes approximately 800μA
from a single 5V supply.
Simple Data Acquisition System Takes Advantage of the LTC1598’s
MUXOUT/ADCIN Pins-to-Filter Analog Signals Prior to A/D Conversion
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
CH5
CH6
CH7
GND
CLK
CSMUX
D
IN
COM
GND
CSADC
D
OUT
NC
CH4
CH3
CH2
CH1
CH0
V
CC
MUXOUT
ADCIN
V
REF
V
CC
CLK
NC
LTC1598
ANALOG INPUTS
0V TO 5V
RANGE
7.5k
7.5k
1μF
5V
1594/98 TA05
DATA IN
CHIP SELECT
CLOCK
DATA OUT
–
+
1μF
0.015μF
0.03μF
C2
0.1μF
7.5k 7.5k
0.03μF
0.015μF
–
+
C1
0.1μF
5V
1/2
LT1368
1/2
LT1368