Lpc2000

--- In lpc2000@yahoogroups.com, "karldalen" <karldalen@y...> wrote:
> 
> --- In lpc2000@yahoogroups.com, "lp2000c" <lp2000c@e...> wrote:
> > 
> > There's that little gotcha of these parts being 5V tolerant only 
> when 
> > 3.3V is present on the i/o supply.
> > 
> > Since in most designs with 5V and 3.3V, one would likely generate 
> the 
> > 3.3V from the 5V supply, there will likely be a period of time 
when 
> > 5V is present and 3.3V is not.
> > 
> > Unless one adds a bunch of hardware to prevent this, it sort of 
> makes 
> > the 5V tolerant feature worthless.
> 
> Tip!
> 
> Run the regulators(zener+resistor+charge cap) in paralell,
> (not in series)then use a larger charge cap on +5V or if
> a variable regulator are used use a (voltage settling delay)
> cap on adjust pin. It will also add for increased performance
> by filtering noise on the adjust pin!

That's not always an option.  Let's say 5V is coming from a switcher.
Also, what happens on power down.  Depending on drain currents, 3.3V 
(with smaller cap) might discharge before the 5V (with large cap).