Datasheet
100 PA
1k
2.55V
2.5V
+
-
+5V
1k
1k
1k
1k
2.5V
+IN
-IN
OUT
+5V
V
+
100 PA
1k
2.65V
2.55V
+
-
+5V
1k
1k
1k
1k
2.5V
+IN
-IN
OUT
+5V
V
+
LMP8358
SNOSB09B –APRIL 2010–REVISED MARCH 2013
www.ti.com
Degraded Input Line
Figure 59 shows an example of a degraded connection between the bridge and the +IN pin of the LMP8358.
This fault is shown by the 1 kΩ resistor placed between the bridge and the LMP8358. To detect this fault use the
1/50 feature by setting MUX[1:0] to 10b to test the +IN pin, POL to 0b, and G[2:0] to 010b for a gain of 50. This
will give an overall gain of 1. Set CUR[2:0] = 101b to inject a 100µA current and read the output voltage (5082x).
Next set MUX[1:0] to 11b and PIN to 1b to test the −IN pin as shown in Figure 60 and read the output (58C2x). If
the voltages of these two measurements are different a degraded input fault exists.
Figure 59. Degraded Input Line, Step 1
Figure 60. Degraded Input Line, Step 2
Fault Detection Example
Using the fault detection features of the LMP8358 an end product, such as a scale, can periodically test that no
damage has occurred to the system. A routine can be written that could, for example, run on start up, that will
step through the fault detection features shown above and compare the output voltage to a table like that shown
in Table 16. If the circuit shown in Figure 54 is used the values shown in column 2 of Table 16 would show that
the system is working correctly, the values in the columns under the Possible Faults heading would show that
there is a potential problem and that operator attention is needed.
Table 16. Fault Detection Matrix
No Faults Possible Faults
LMP8358 V
OUT
V
OUT
Possible Cause V
OUT
Possible Cause V
OUT
Possible Cause
Register
00 82x 2.5V V
OUT
< CMVR or Input is out of V
+
+IN shorted to V
+
0V +IN shorted to
V
OUT
> CMVR CMVR GND
00 C2x 2.5V V
OUT
< CMVR or Input is out of V
+
−IN shorted to V+ 0V −IN shorted to
V
OUT
> CMVR CMVR GND
50 00x 0.61V V
+
+IN Open 0.07V Inputs shorted
50 03x 4.97V V
+
−IN 0.7V Inputs shorted
50 82x 2.55V 2.65V* Degraded +IN line
58 C2x 2.55V 2.55V* Degraded +IN line
50 82x 2.55V 2.55V* Degraded −IN line
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