Lpc2000

Hi Rich,

for the micro you only need the 1.8V to be stable. So your voltage
regulator has to produce the 1.8V even if the battery is far below 3V.
For the I/O it is possible to run it with less than 3V but driving
capabilities and speed will suffer, don't ask me how much. IMHO you
can go down with the I/O voltage to probably 2.4V before this becomes
n issue as long as the remaining parts of your board don't need the
output voltage of the digital signals to be in the range of 3V.

May be this help, Bob

--- In lpc2000@yahoogroups.com, "Richard" <richas@y...> wrote:
> On second examination of this "chicken and egg" issue I have another,
> simpler solution.  The TPS78918 regulator has very low quiescent
> current, I can feed this directly from the batteries and use the
> charge pump only for the IO.  The core voltage will be directly as the
> battery voltage drops and the charge pump boosts for the IO.
> 
> Rich
> 
>  --- In lpc2000@yahoogroups.com, "Richard" <richas@y...> wrote:
> > Greetings all,
> >      I am designing a battery powered app. and am considering
> > different scanarios with regard to low power modes and charge pumps. 
> > I am considering the TI TPS60213 charge pump to boost the 3V battery
> > voltage as they run down.  The "active mode" quiescent current of the
> > charge pump is too high but there is a "snooze" mode of 2uA.  Snooze
> > mode is entered by bringing a pin low, maximum current supplied by the
> > charge pump in snooze mode is 2mA.
> > The processor (2106) will be drawing much more than this when it
> > triggers snooze mode but I plan to have a large enough cap on the
> > supply so that it will be able to supply enough energy with the
> > asssumption that the micro immediatly goes into powerdown following
> > the line of code that sends the charge pump into snooze mode.  The
> > charge pump has a "power-good" signal that can be used to wake up the
> > micro.
> > When the micro is asleep and the charge pump is in snooze mode a
> > "wake-up" by a button has to wake up the charge pump first by
> > asserting the snooze pin.  the micro will drive the snooze pin through
> > a resistor, the button will over-ride the micro signal.  When the
> > micro wakes up IT asserts the snooze button, latching the signal, and
> > then the finger goes away.
> > 
> > Anyone else have another solution?
> > 
> > Rich