LTC1594 Linear Technology, LTC1594 Datasheet - Page 21

• Manufacturer Part Number: LTC1594
• Description: 4- and 8-Channel/ Micropower Sampling 12-Bit Serial I/O A/D Converters
• Manufacturer: Linear Technology

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 0.1 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
ANALOG INPUTS
0V TO 5V
RANGE
10
11
12
1
2
3
4
5
6
7
8
9
CH5
CH6
CH7
GND
CLK
CSMUX
D
COM
GND
CSADC
D
NC
IN
OUT
MUXOUT/ADCIN Pins-to-Filter Analog Signals Prior to A/D Conversion
LTC1598
Simple Data Acquisition System Takes Advantage of the LTC1598’s
MUXOUT
ADCIN
U
V
CH4
CH3
CH2
CH1
CH0
CLK
V
V
REF
NC
CC
CC
24
23
22
21
20
19
18
17
16
15
14
13
N
5V
DATA OUT
DATA IN
CHIP SELECT
CLOCK
1 F
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 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 800 A
from a single 5V supply.
7.5k
C2
0.1 F
P-P
0.03 F
1 F
0.015 F
7.5k
offset sine input.
LT1368
1/2
5V
+
–
–
+
LTC1594/LTC1598
LT1368
7.5k
1/2
0.015 F
0.03 F
7.5k
1594/98 TA05
C1
0.1 F
21