Datasheet

4V
4V
1.5k
3V
+
-
+5V
1k
1k
1k
1k
+IN
-IN
OUT
+5V
V
+
+
-
+5V
1k
1k
1k
1k
2.5V
2.5V
+IN
-IN
OUT
+5V
V
+
LMP8358
SNOSB09B –APRIL 2010–REVISED MARCH 2013 www.ti.com
The Fault Detection Current bit, CUR[2:0] controls the amount of current that sent to the input pin as shown in
Table 15.
Table 15. Fault Detection Current Source (Register bits 14:12)
CUR2 CUR1 CUR0
0 0 0 disconnected and powered down *
0 0 1 10 nA
0 1 0 100 nA
0 1 1 1 μA
1 0 0 10 µA
1 0 1 100 µA
1 1 0 disconnected, but powered *
1 1 1 Do Not Use
* Leaving the fault detection current source powered allows it to switch between current levels faster, particularly
when supplying currents less than 1 µA.
FAULT DETECTION METHODS
Using the Multiplexer, Polarity, and Current features the end user can detect faults in the system between the
sensor and the LMP8358. These examples will use the set up shown in Figure 54 which shows a bridge sensor
connected through some cabling to a supply and the LMP8358. The fault detection methods are described
below.
Figure 54. Bridge Connected to the LMP8358 With No Problems
Common Mode Out of Range
Figure 55 shows an example of a degraded connection between the bottom of the bridge and ground. This fault
is shown by the 1.5 kΩ resistor placed between the bridge and ground. This will raise the common mode at the
inputs of the LMP8358 to 4V, which is out of the CMVR. To determine the common mode voltage at the input
pins, use the 1/50 feature by setting MUX[1:0] to 10b to test the +IN pin or to 11b to test the −IN pin, POL to 0b,
and G[2:0] to 010b for a gain of 50 (0082x or 00C2x). This will give an overall gain of 1 and the output will read
4V for either MUX setting.
Figure 55. Degraded Connection Between the Bottom of the Bridge and Ground
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