LTC2421 LINER [Linear Technology], LTC2421 Datasheet - Page 27

• Manufacturer Part Number: LTC2421
• Description: 1-/2-Channel 20-Bit UPower No Latency ADCs in MSOP-10
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
resistance R
removed by the FS
scale output of the ADC (data out = FFFFF
at V
errors due to R
ZS
00000
R
leakage current at pins FS
dynamic input range (– 300mV to 5.3V) and low noise
(1.2ppm RMS) enable the LTC2421 or the LTC2422 to
directly digitize the output of the bridge sensor.
The LTC2422 is ideal for applications requiring continu-
ous monitoring of two input sensors. As shown in
Figure 32, the LTC2422 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.
P3
SET
IN
to R
. The absolute zero output of the ADC (data out =
HEX
= V
P5
Figure 29. Errors Due to Excitation Currents
) occurs at V
B
= FS
have negligible errors due to the 1nA (typ)
I
P1
EXCITATION
P2
in series with the half-bridge sensor are
SET
are removed by the ground sense input
SET
U
, see Figure 31. Similarly, the offset
R
R
input to the ADC. The absolute full-
IN
P1
P2
SENSOR
THERMISTOR
= V
U
SET
+
–
+
–
A
V
V
FULL-SCALE ERROR
OFFSET ERROR
100
= ZS
, ZS
+
–
12k
SENSOR OUTPUT
SET
SET
W
. Parasitic resistors
COLD JUNCTION
THERMOCOUPLE
Figure 32. Isolated Temperature Measurement
and V
+
24212 F29
HEX
IN
) will occur
2.7V TO 5.5V
. The wide
U
–
1
2
3
4
5
V
FS
CH1
ZS
CH0
CC
SET
SET
LTC2422
GND
SDO
SCK
CS
F
Figure 31. Transfer Curve with Zero-Scale and Full-Scale Set
O
10
9
8
7
6
00000
FFFFF
I
EXCITATION
ISOLATION
H
H
Figure 30. Half-Bridge Digitizer with
Zero-Scale and Full-Scale Sense
BARRIER
R
R
V
V
P1
P2
ZS
B
A
SET
PROCESSOR
I
I
I
DC
DC
DC
R
R
R
P3
P4
P5
0
0
0
LTC2421/LTC2422
24212 F32
2
3
5
6
V
FS
V
GND
ZS
IN
IN
SET
LTC2421
SET
V
CC
1
SDO
SCK
CS
F
O
FS
9
8
7
10
SET
24212 F03
3-WIRE
SPI INTERFACE
12.5%
EXTENDED
RANGE
12.5%
UNDER
RANGE
24212 F31
27
24212f