Lpc2000

Robert,
I've found in the older posts that the current on VBAT is 15-20uA
(very, very much! Standalone RTCs consumes 250-500nA in broad range of
voltage). 
OK, I estimated the life time of the RTC using 1F cap. It is about 5
hours only. And it should be let's say a couple of weeks! Such long
breaks are normal in my application. My customers wouldn't be happy if
I make them to set the time after any power-up.

I can see that the best solution is using the external RTC chip. 
Darek


--- In lpc2000@yahoogroups.com, Robert Adsett <subscriptions@a...>
wrote:
> 
> Have you considered a supercap?  A couple of Farads may be all you
need 
> depending on how long a power outage you want to withstand.  A
simple 
> resistor diode combination will then keep it charged when the power
is on.
> 
> Robert
> 
> " 'Freedom' has no meaning of itself.  There are always
restrictions,   be 
> they legal, genetic, or physical.  If you don't believe me, try to
chew a 
> radio signal. "  -- Kelvin Throop, III
> http://www.aeolusdevelopment.com/