When Pin 5 (Vcc) of SN74AHC1G09 is low (or connected to ground), what happens when an external high is put on the inputs or the output?
If there is no supply your gate will be powered over the signal lines (gate protection diodes at input, bulk diodes at output). But: If you tie Vcc to GND the diodes will be in forward direction to GND, hence you will get some hundred mV at the pins, depending on how strong your signal is (plus a little bit of heat, ...).
Best regards,Edwin Krasser
I think you answered my question. Some schematics of the inputs/outputs would be helpful.
I assume the output will look like a pair of anti-parallel diodes. Is this the same as the bulk diodes you are referring to?
You should easily find some literature about CMOS schematics on the websites of TI, NXP, ... . Just look for the different CMOS family guides (HC, AHC, LVC, ...).
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