Lpc2000

--- 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..?