Datasheet

36
LTC2420
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PART NUMBER DESCRIPTION COMMENTS
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ON
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LTC2413 24-Bit No Latency ∆Σ ADC Simultaneous 50Hz to 60Hz Rejection 0.16ppm Noise
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2420f LT/LCG 1000 4K • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2000
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone]
●
FAX: [phone]
●
www.linear-tech.com
TYPICAL APPLICATIO
U
The circuit shown in Figure 41 enables pseudodifferential
measurements of several bridge transducers and abso-
lute temperature measurement. The LTC1391 is an
8-to-1 analog multiplexer.
Consecutive readings are performed on each side of the
bridge by selecting the appropriate channel on the
LTC1391. Each output is digitized and the results digitally
subtracted to obtain the pseudodifferential result. Several
bridge transducers may be digitized in this manner.
In order to measure absolute temperature with a thermo-
couple, cold junction compensation must be performed.
Channel 6 measures the output of the thermocouple while
channel 7 measures the output of the cold junction sensor
(diode, thermistor, etc.). This enables digital cold junc-
tion compensation of the thermocouple output. The tem-
perature measurement may then be used to compensate
the temperature effects of the bridge transducers.
CH1
CH0
THERMOCOUPLE
THERMISTOR
CH3 OUT
GND
LTC1391
LTC2420
2420 F41
V
REF
V
IN
GND
V
CC
V
CC
F
O
SCK
SDO
CS
CH4
CH5
CH6
CH7
CH2
Figure 41. Pseudodifferential Multichannel Bridge Digitizer
and Digital Cold Junction Compensation