Lpc2000

At 01:00 PM 4/20/05 +0000, drybak2000 wrote:
>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?

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/