How to have an accurate ADC?(STM32)
Just putting this here in case anyone is still wondering
Ts: 1.5
Radc: 1
Fadc: 14
Cadc: 8
N: 12


And after calculation, this is what I get = -0.9986 A negetive number? why? There are a table below the discription of this equation. table 60. Rain max for Fadc=14MHz . For Ts=1.5 Rain is 0.4kOhm and I expect to get a value close to this but what I get so far is a negetive value.

Well, you got the right values but not units.
Ts: 1.5 [dimensionless]
Radc: 1 [kilohms]
Fadc: 14 [megahertz]
Cadc: 8 [picofarads]
N: 12 [dimensionless]

If you then plug in everything as standard SI units you'll get a standard SI unit as a result. So, instead of 1 for Radc you have to substitute 1000, instead of 8 for Cadc you have to substitute 8e-12 or 8*10^(-12).
If you do that, for the values you provided, you get a result of around 380 and it's in ohms, so it matches the table value of 0.4kΩ.