[time-nuts] Clock level conversion 5V -> 3.3V

Hal Murray hmurray at megapathdsl.net
Tue Sep 30 23:10:50 EDT 2014


vesoares at deea.isel.ipl.pt said:
> I would suggest some 3.3V logic (inverter) gate with 5V tolerant inputs
> from Little Logic TI portfolio. There are buffered and unbuffered gate
> available. 

What's the advantage of a chip over a pair of resistors?

haunma at keteu.org said:
> I have seen a resistive divider used in a similar application, but wondered
> if I could save the couple dozen mA they were spending. 

Power might be one.  If it's a long enough run that you need a termination, 
then the power doesn't cost anything extra.  If it's only a few inches, you 
can use higher values of resistance to save the power.

For a given value of resistance and a specific chip, there should be some 
crossover frequency where the power of the chip matches the power of the 
resistors.  It might be fun to play with the numbers.



-- 
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