Did anybody ever figure out anything regarding battery life and
the RTC ?? In my LPC2103 application, I'm seeing the battery voltage
coming down 0.2 volts in just a few days. 3.1 something to around
2.7 something today.
I wonder also, if maybe if there is a particular 32.769 kHz xtal that
might be recommended ? I can certainly see the RTC operating off
of the normal 3.3 volt supply instead of battery, but I would
think there would be either diodes and/or an extra external transistor
to switch from one supply to the other (battery) when non-coin cell
power is removed. Maybe a little SOT23 FET gating on from 5 volts
on the board. Hmmmm.... Might be a solution I suppose.
boB
--- In l..., "Grant Sullivan" wrote:
>
> Hi,
>
> You can run the LPC2138 RTC from Vbatt with Vdd = 0volts.
>
> The only draw back I see is the size off battery to keep the RTC alive
> for a long period of time when Vdd = 0. I have not been able to
> find current comsumption numbers for the RTC. It would
> be interesting however to compare them with the current draw
> of an external RTC solution.
>
> I can only get about 4months before may RTC battery goes flat.
> The battery I use is Renata CR1025FV-LF 30mAh.
>
> I was thinking of going to a external RTC solution but it is so
> handy from a programming and manufacturing stand point to have
> the RTC in the Micro.
>
> Grant
> NZ
>
>
>
> -----Original Message-----
> From: l... [mailto:l...]
> On Behalf Of Darcy Williams
> Sent: Wednesday, 2 May 2007 8:34 a.m.
> To: l...
> Subject: [lpc2000] LPC2138 and RTC running from vBatt
>
>
>
> Is it possible to run the RTC from vBatt while Vdd is sitting at
> 0V?
> There seem to be mixed opinions of this on the forum and the
> data
> sheet is anything but specific. There are details about how many
> uA
> the RTC draws from vBatt when the LPC is in power-down mode, but
> nothing about the current draw when the only thing being powered
> is
> the RTC with power removed from everything else.
>
> Can this be done or are we doing to need an external RTC? Are
> there
> any dirt-cheap SPI RTCs around?
>
> Thanks!
>
>
>
>
>
>
>