Lpc2000

At 11:35 PM 3/5/2006 +0000, rtstofer wrote:
>--- In lpc2000@yahoogroups.com, "Sutton Mehaffey" <sutton@...> wrote:
> > I expect to put a tantalum cap of perhaps 1uf or so on the voltage
> > divider junction and sample very infrequently, perhaps once per
> > second. Perhaps it is "no worries" about what the analog input leakage
> > current  is  in such circumstances.  If it is 4ua then the offset on a
> > 100k  source  Z  would be only about 40mv and reflected up the divider
>
>Other manufacturers (notably Microchip) specify that the source
>impedance of analog signals must be below 10k ohms.  I certainly
>wouldn't be driving the converter with 100k.

He won't driving the input with 100K (from what I read of his description 
anyway), he'll be driving it with a 1uF cap.  It presumably has a 
resistance well below 100KOhms.  That should also swamp the input 
capacitance on the sample and hold.  Now, he just needs to concerned about 
the leakage across the cap as well.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
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