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opinion on 74HCT05 open drain to high voltage level shift

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xaccto

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74HCT05 hex inverter with open drain

I want to tied the drain through pull-up resistor to ~15V+

I have read the 74HCT05 spec sheet many times and I'm not sure if it rules it out....
I don't need much pull-up current ~20uA more than enough
should the output mosfet in the chip fail from this ? a drain-source breakdown presumably...

The goal is to buffer the control inputs to CD4066, which at 15V VDD need minimum VIH 8.4V
which need to be controlled from PIC outputs.....

if I can't use 74HCT05 then need to resort to using transistors+resistors which would use up
a lot of PCB real-estate
 

Unfortunately it will not work. That particuar type has a diode betwen it's open drain output and VCC connection will will conduct if you pull up to higher than VCC. I'm not sure if high voltage HCT parts are available but if you can change to an LS type instead, you can use either the 74LS06 or 74LS07 which are functional equivalents with 30V and 15V rated outputs respectively.

Brian.
 
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