Lpc2000

Is this really true?  At power-up if I apply 5V for microseconds (or 
milliseconds) before 3.3V the "5V tolerant" I/O feature does not 
work?  What happens, does the part latch-up or do some horrible 
thing?  How serious is this problem?
James



Message: 20        
   Date: Wed, 15 Dec 2004 00:56:37 -0000
   From: "karldalen" <karldalen@...>
Subject: Re: Alternative Circuit, 5v 3,6 v IO pröblem!


--- 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!

>Or set every +5V external IC's in tristate at power on!! Urg!!

>REG
>KD