ADUCM360/361 ADC input or external reference short/open detection

Document created by analog-archivist Employee on Feb 23, 2016
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Can an open/short on an ADC input or external reference input be detected?  I
want to be  sure that wiring issues can be detected in my application.

 

The ADuCM360/361 provides 2x 50uA diagnostic current sources.  When switched
on, these current sources can be selected to output current on any ADC input.

a.To detect a short:
Enable the current source to connect to one of the inputs.(For example,
ADC1CON[11:10] = [01]) Normally the ADC result should be 50uA*R1. If a short is
present,
the ADC result will be ~0V.

b.To detect an open connection to an ADC input:
Enable the current source to two Analog input pins: (For example,
ADC1CON[11:10] = [11])
Normally, the ADC result should be 50uA*(R1.-R2)
If the ADC result is larger than even the worst case matching of R1 and R2, an
open  connection is detected.

c.An error on the external reference inputs is detected using the DETSTA[4]
status bit.
This bit is set to 1 if the external reference source connected to VRFE+/VREF-
is <= 400mV.
Note, this bit is not valid for the EXTREF2IN+/EXTREF2IN- inputs.

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