> Van: Spehro Pefhany <speff@INTERLOG.COM>
> Aan: PICLIST@MITVMA.MIT.EDU
> Onderwerp: Re: [EE]: I2C Real Time Clock
> Datum: maandag 16 oktober 2000 14:50
>
> At 11:04 AM 10/16/00 +0200, you wrote:
> >> Van: Jinx <joecolquitt@CLEAR.NET.NZ>
> >> Aan: PICLIST@MITVMA.MIT.EDU
> >> Onderwerp: Re: [EE]: I2C Real Time Clock
>
> >Yes, but I'm switching between two voltages, one for the "active" state
of
> >the whole device (5.0 volts), one for the "dormant" state (device
powered
> >down, only the clock keeps on running off a NICAD or similar).
>
> The only number I see listed in the data sheet related to this is the
> "typical" figure of 0.2ppm/100mV, which would be typically 5ppm if it is
> linear (and I would definitely verify *that* with a good reciprocal
frequency
> meter) for a change from 2.4V -> 5V, maybe double or triple this for a
> realistic "maximum".  Is that the kind of thing you are seeing?

Well, it think it must be related to it.  The real problem is that I'm
providing the RTC with two different voltages: One when the device (the RTC
is in) is ON, one when it's OFF.  Maybe I should just give it 2.4 volts
(off the NiCad, charging it from the main supply), and be done with it.

But it still mistifies me.  I can't say I've seen any schematics (from the
producers of the chip) handling this problem though ...

Regards,
  Rudy Wieser

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