Datasheet

27
LTC2401/LTC2402
APPLICATIO S I FOR ATIO
WUUU
at V
IN
= V
B
= FS
SET
, see Figure 29. Similarly, the offset
errors due to R
P2
are removed by the ground sense input
ZS
SET
. The absolute zero output of the ADC (data out =
000000
HEX
) occurs at V
IN
= V
A
= ZS
SET
. Parasitic resistors
R
P3
to R
P5
have negligible errors due to the 1nA (typ)
leakage current at pins FS
SET
, ZS
SET
and V
IN
. The wide
dynamic input range (–300mV to 5.3V) and low noise
(0.6ppm RMS) enable the LTC2401 or the LTC2402 to
directly digitize the output of the bridge sensor.
The LTC2402 is ideal for applications requiring continu-
ous monitoring of two input sensors. As shown in
Figure 30, the LTC2402 can monitor both a thermocouple
temperature probe and a cold junction temperature sen-
sor. Absolute temperature measurements can be
performed with a variety of thermocouples using digital
cold junction compensation.
The selection between CH0 and CH1 is automatic. Initially,
after power-up, a conversion is performed on CH0. For
each subsequent conversion, the input channel selection
is alternated. Embedded within the serial data output is a
status bit indicating which channel corresponds to the
conversion result. If the conversion was performed on
CH0, this bit (Bit 30) is LOW and is HIGH if the conversion
was performed on CH1 (see Figure 31).
Figure 29. Transfer Curve with Zero-Scale and Full-Scale Set
Figure 30. Isolated Temperature Measurement
00000
H
12.5%
UNDER
RANGE
ADC DATA OUT
FFFFF
H
ZS
SET
FS
SET
V
IN
24012 F29
12.5%
EXTENDED
RANGE
V
CC
F
O
FS
SET
ZS
SET
SCK
CH1 SDO
GND
CS
THERMOCOUPLE
COLD JUNCTION
ISOLATION
BARRIER
PROCESSOR
CH0
–+
110
12k
THERMISTOR
100Ω
9
8
7
6
2
3
4
5
2.7V TO 5.5V
LTC2402
24012 F30