ltc1598l Linear Technology Corporation, ltc1598l Datasheet - Page 21

• Manufacturer Part Number: ltc1598l
• Description: 4- And 8-channel, 3v Micropower Sampling 12-bit Serial I/o A/d Converters
• Manufacturer: Linear Technology Corporation

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 F 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
TYPICAL APPLICATIONS
7.5k
R1
20
21
22
23
24
1
2
3
8 COM
C1
0.03 F
LTC1598L
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
7.5k
R2
8-CHANNEL
MUXOUT/ADCIN Pins to Filter Analog Signals Prior to A/D Conversion
Simple Data Acquisition System Takes Advantage of the LTC1598L’s
MUX
C2
0.015 F
MUXOUT
U
18
3
2
N
+
–
1/2 LT1368
17
ADCIN
3.3V
+
8
SAMPLING
–
12-BIT
GND
ADC
16
V
4, 9
REF
1
C8
0.01 F
3.3V
V
CC
15, 19
CSMUX
1594L/98L TA05
CSADC
D
CLK
OUT
D
7.5k
R3
NC
NC
IN
than 1LSB of error due to offsets and bias currents. The
filter’s noise and distortion are less than –72dB for a
100Hz, 2V
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 A
from a single 3V supply.
C3
0.1 F
10
6
5, 14
7
11
12
13
C4
0.03 F
7.5k
R4
C7
1 F
SERIAL DATA LINK
MICROWIRE AND SPI
COMPATIBLE
P-P
offset sine input.
C5
0.015 F
LTC1594L/LTC1598L
5
6
–
+
1/2 LT1368
4
7
C6
0.1 F
21
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