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Subject: Vcc pin disconnection in CMOS ICs.

Date: 08/16/00 at 12:09 AM
Posted by: SC Mishra
E-mail: dsig5@rdso.railnet.gov.in
Message Posted:

In CMOS ICs, it is found that when external power ( 5 volts) is disconnected due to disconnection at pin or at PCB even then IC continues to work if one of its input is at logic HIGH ( 5 volts). This is due to surge diodes in side the ICs which connect input to ground/Vcc. When all input to such IC at logic LOW ( 0 volts) the IC does not work. Thus functioning of IC under such defect becomes unpredictable. Moreover it becomes deficult to identyfy such faults in working system.

Thus if such ICs are used in Safety Systems , it becomes impossible to dectect such faults where as system safety gets drastically reduced. I request all to suggest any means to handle such situation.


SC Mishra

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