LTC2408CG#TR Linear Technology, LTC2408CG#TR Datasheet - Page 27

• Manufacturer Part Number: LTC2408CG#TR
• Description: IC ADC 24BIT 8CH MICROPWR 28SSOP
• Manufacturer: Linear Technology

Specifications of LTC2408CG#TR

• Number Of Bits: 24
• Sampling Rate (per Second): 7.5
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP (0.200", 5.30mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
quently, these resistors should be low temperature coef-
ficient devices. The use of higher resistance RTDs is not
recommended in this topology, although the inclusion of
one 1000 RTD at the top on the ladder will have minimal
impact on the lower elements. The same caveat applies to
fast changing temperatures. Any fast changing sensors
should be at the top of the ladder.
The LTC2408’s Uncommitted Multiplexer Finds Use in
a Programmable Gain Scheme
If the multiplexer in the LTC2408 is not committed to
channel selection, it can be used to select various signal-
processing options such as different gains, filters or at-
tenuator characteristics. In Figure 25, the multiplexer is
shown selecting different taps on an R/2R ladder in the
feedback loop of an amplifier. This example allows selec-
tion of gain from 1 to 128 in binary steps. Other feedback
networks could be used to provide gains tailored for
specific purposes. (For example, 1x, 1.1x, 1.41x, 2x,
2.028x, 5x, 10x, 40x, etc.) Alternatively, different bandpass
PLATINUM
Figure 24. Measuring Up to Seven RTD Temperatures with One Reference Resistor and One Reference Current
100
RTD
PT1
PT2
PT7
UP TO SEVERAL
HUNDRED FEET.
WIRE TYPE
U
ALL SAME
TO PT3-PT6
INFORMATION
U
R1
20.1k
0.1%
+
47 F
W
300 A
LTC1634-2.5
PROTECTION
RESISTORS
OPTIONAL
5k MAX
5V
6
4
R2
U
5
10
11
12
13
14
15
17
9
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
3
2
R2
+
–
8-CHANNEL
LTC1050
MUX
characteristics or signal inversion/noninversion could be
selected. The R/2R ladder can be purchased as a network
to ensure tight temperature tracking. Alternatively, resis-
tors in a ladder or as separate dividers can be assembled
from discrete resistors. In the configuration shown, the
channel resistance of the multiplexer does not contribute
much to the error budget, as only input op amp current
flows through the switch. The LTC1050 was chosen for
its low input current and offset voltage, as well as its
ability to drive the input of a
Insert Gain or Buffering After the Multiplexer
Separate MUXOUT and ADCIN terminals permit insertion
of a gain stage between the MUX and the ADC. If passive
filtering is used at the input to the ADC, a buffer amplifier
is strongly recommended to avoid errors resulting from
the dynamic ADC input current. If antialiasing is required,
it should be placed at the input to the MUX. If bandwidth
limiting is required to improve noise performance, a filter
with a –3dB point at 1500Hz will reduce the effective total
5V
7
4
MUXOUT
1, 5, 6, 16, 18, 22, 27, 28
R3
OPTIONAL
GAIN
BLOCK
6
7
4
ADCIN
24-BIT
GND
LTC2408
ADC
3
V
REF
LTC2404/LTC2408
V
0.1 F
CC
2, 8
CSMUX
CSADC
2404/08 F24
SDO
SCK
CLK
D
IN
F
O
26
23
20
25
19
21
24
ADC.
5V
V
1 F
CC
27