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If an output terminal receives current externally, e.g. for
bidirectional inputs and outputs, the output rail must not
be floating (i.e. open-circuit)
Reason
The supply voltage is fed back to the output rail via the
integrated protective diode in the output. If a second output
connected to the same potential is switched, the load of this
output is fed through the transistor of the first output thus
causing the first output to overload and fail.
This needs special attention when unit and output voltage
supply are fused separately and when the output rail VBB
R
is
switched off by the software via the integrated relay. If
necessary, the supply voltage should be monitored via the
appropriate hardware and software measures.
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