LTC2983
22
2983fc
For more information www.linear.com/LTC2983
Table 14. Sensor Configuration
(3) SENSOR CONFIGURATION
SGL OC
CHECK
OC CURRENT SINGLE-ENDED/
DIFFERENTIAL
OPEN-CIRCUIT
CURRENT
B21 B20 B19 B18
0 0 X X Differential External
0 1 0 0 Differential 10µA
0 1 0 1 Differential 100µA
0 1 1 0 Differential 500µA
0 1 1 1 Differential 1mA
1 0 X X Single-Ended External
1 1 0 0 Single-Ended 10µA
1 1 0 1 Single-Ended 100µA
1 1 1 0 Single-Ended 500µA
1 1 1 1 Single-Ended 1mA
APPLICATIONS INFORMATION
(3) Sensor Configuration
The sensor configuration field (see Table 14) is used
to select single-ended (B21=1) or differential (B21=0)
input and allows selection of open circuit current
if internal open-circuit detect is enabled (bit B20).
Single-ended readings are measured relative to the
COM pin and differential are measured between the
selected CH
TC
and adjacent CH
TC-1
(see Figure 4).
If open-circuit detection is enabled, B20=1, then the user
can select the pulsed current value applied during open-
circuit detect using bits B18 and B19 . The user determines
the value of the open circuit current based on the size of
the external protection resistor and filter capacitor (typically
10µA). This network needs to settle within 50ms to 1µV
or less. The duration of the current pulse is approximately
8ms and occurs 50ms before the normal conversion cycle.
Thermocouple channel assignments follow the general
convention shown in Figure 4. The thermocouple positive
terminal ties to CH
TC
(where TC is the selected channel
number) for both the single-ended and differential modes
of operation. For single-ended measurements the thermo-
couple negative terminal and the COM pin are grounded.
The thermocouple negative terminal is tied to CH
TC-1
for differential measurements. This node can either be
grounded or tied to a bias voltage.
(4) Custom Thermocouple Data Pointer
See Custom Thermocouples section near the end of this
data sheet for more information.
Figure 4. Thermocouple Channel Assignment Convention
SINGLE-ENDED
+
–
+
–
= CH
TC
(1≤ TC ≤ 20)
COM
CH
TC
0.1µF
CHANNEL
ASSIGNMENT
DIFFERENTIAL
2983 F04
= CH
TC
(2≤ TC ≤ 20)
CH
TC
CH
TC-1
0.1µF
CHANNEL
ASSIGNMENT
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