[time-nuts] Modeling vs reality question re my TIC

[Bob Stewart]

Fellow Timenuts:


I'm trying to square reality with the modeling that I did, and nothing makes 
sense.  When I modeled the result of just my 2.4K resistor with the caps and resistor the PIC datasheet says it has in it, there's no relationship.  The model says 
I'll get millivolts out.  Here's how I calculate what I'm actually 
getting:

ADC VRef is 2.5V
10-bit ADC = 1024 positions


Max ADC from TIC = 975
975/1024*2.5 = 2.38V Max TIC value


Min ADC from TIC = 293
293/1024*2.5 = 0.715V Min TIC value

A range of 0.715V-2.38V is totally outside my expectations.  The only way I can get close to these values is if the internal CHOLD in the PIC is only a fraction of the 120pf they say it has - say 20pf.  Any thoughts would be appreciated.

Bob - AE6RV