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 k

Ω 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

28

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