Lpc2000

OK that's fine, but it doesn't solve the problem - RTC will be powered
from battery all the time (even if main power supply is OK). I don't
think that a small battery will last long (I can't find any
information about current on VBAT).

Darek

--- In lpc2000@yahoogroups.com, "valdef78" <valdef@s...> wrote:
> 
> --- In lpc2000@yahoogroups.com, "drybak2000" <d.rybak@j...> wrote:
> > 
> > I don't understand the idea of VBAT in LPC2138. 
> > 
> > I want to have RTC running in case of main power supply failure. 
> > 
> > I didn't find any information about a battery backup switch in 
> LPC. So
> > if I connect a battery to VBAT, RTC is powered from the battery 
> all the
> > time. I'm afraid that the life of my battery will not be long. 
> > 
> > I can add an external battery switch (one of ADM.. or MAX..) but
> > Li-Ion batteries are 3.0V or 3.6V. In case of a 3.0V battery the
> > voltage drop on the switch causes that VBAT is outside of
> > specification. In case of a 3.6V battery the switch doesn't work
> > (battery voltage is higher then main power voltage!). 
> > 
> > Have anybody solved this problem?
> > 
> > Darek
> 
> Use a simple 1.2V battery with a low quiescent current 3.3V step-up 
> from Maxim or other..?