LMP8358MA NSC [National Semiconductor], LMP8358MA Datasheet - Page 28

• Manufacturer Part Number: LMP8358MA
• Description: Zero-Drift, Programmable Instrumentation Amplifier with Diagnostics
• Manufacturer: NSC [National Semiconductor]

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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
* The values shown for a degraded input line will vary de-
pending on the resistance in the line. This table uses the value
in
LMP8358
Register
00 82x
00 C2x
50 00x
50 03x
50 82x
58 C2x
50 82x
58 C2x
Figure 12
and
V
2.5V
2.5V
0.61V
4.97V
2.55V
2.55V
2.55V
2.55V
No Faults
OUT
Figure
13, 1kΩ.
V
V
V
V
V
V
V
2.65V*
2.55V*
2.55V*
2.65V*
OUT
OUT
OUT
OUT
OUT
+
+
< CMVR or
> CMVR
< CMVR or
> CMVR
Table 16. Fault Detection
Table 16. Fault Detection Matrix
Possible Cause
Input is out of
CMVR
Input is out of
CMVR
+IN Open
−IN
Degraded +IN
line
Degraded +IN
line
Degraded −IN
line
Degraded −IN
line
28
Matrix. If the circuit shown in
shown in column 2 of
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.
V
V
V
0.07V
0.7V
Possible Faults
OUT
+
+
Possible Cause
+IN shorted to V
−IN shorted to V+ 0V
Inputs shorted
Inputs shorted
Table 16. Fault Detection Matrix
+
Figure 7
V
0V
OUT
is used the values
Possible Cause
+IN shorted to
GND
−IN shorted to
GND
would