LTC2424 Linear Technology, LTC2424 Datasheet - Page 23

• Manufacturer Part Number: LTC2424
• Description: 4-/8-Channel 20-Bit uPower No Latency ADCs
• Manufacturer: Linear Technology

APPLICATIONS
As a result of the oversampling ratio (256) and the digital
filter, minimal (if any) antialias filtering is required in front
of the LTC2424/LTC2428. If passive RC components are
placed in front of the LTC2424/LTC2428, the input dy-
namic current should be considered. In cases where large
effective RC time constants are used, an external buffer
amplifier may be required to minimize the effects of input
dynamic current.
The modulator contained within the LTC2424/LTC2428
can handle large-signal level perturbations without satu-
rating. Signal levels up to 40% of V
analog modulator. These signals are limited by the input
ESD protection to 300mV below ground and 300mV above
V
The LTC2428’s Resolution and Accuracy Allows You
to Measure Points in a Ladder of Sensors
In many industrial processes, for example, cracking tow-
ers in petroleum refineries, a group of temperature mea-
surements must be related to one another. A series of
platinum RTDs that sense slow changing temperatures
CC
.
Figure 22. Measuring Up to Seven RTD Temperatures with One Reference Resistor and One Reference Current
PLATINUM
100
RTD
PT1
PT2
PT7
U
UP TO SEVERAL
HUNDRED FEET.
WIRE TYPE
ALL SAME
INFORMATION
TO PT3-PT6
U
REF
R1
20.1k
0.1%
W
+
do not saturate the
47 F
300 A
LTC1634-2.5
PROTECTION
RESISTORS
OPTIONAL
5k MAX
U
5V
6
4
R2
5
10
11
12
13
14
15
17
9
5 ZS
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
SET
3
2
R2
can be configured into a resistive ladder, using the LTC2428
to sense each node. This approach allows a single excita-
tion current passed through the entire ladder, reducing
total supply current consumption. In addition, this ap-
proach requires only one high precision resistor, thereby
reducing cost. A group of up to seven temperatures can be
measured as a group by a single LTC2428 in a loop-pow-
ered remote acquisition unit. In the example shown in
Figure 22, the excitation current is 240 A at 0 C. The
LTC2428 requires 300 A, leaving nearly 3.5mA for the
remainder of the remote transmitter.
The resistance of any of the RTDs (PT1 to PT7) is deter-
mined from the voltage across it, as compared to the
voltage drop across the reference resistor (R1). This is a
ratiometric implementation where the voltage drop across
R1 is given by V
the voltage on a representative length of wire. If the same
type and length of wire is used for all connections, then
errors associated with the voltage drops across all wiring
can be removed in software. The contribution of wiring
drop can be scaled if wire lengths are not equal.
+
–
8-CHANNEL
LTC1050
MUX
5V
7
4
MUXOUT
1, 6, 16, 18, 22, 27, 28
R3
OPTIONAL
GAIN
BLOCK
6
7
4
ADCIN
REF
+
–
– V
20-BIT
GND
LTC2428
ADC
3
FS
CH1
LTC2424/LTC2428
SET
. Channel 7 is used to measure
V
0.1 F
CC
2, 8
CSMUX
CSADC
24248 F22
SDO
SCK
CLK
D
F
IN
O
26
23
20
25
19
21
24
5V
V
1 F
CC
23