PIC18f ADC voltage reference

[amilaachala]

hi guys,

I want to know about 'minimum external voltage references' that can be given to ADC.suppose i give external voltage references as " 0 V and 3.3 V " then a step size would be ( 3.3/1023 ) V rit????

thanks ........

 

[Tahmid]

Step Count = (VREF / (Total No. of Steps)) * ADC result

Step size = VREF/(Max count)
So, the step size would be (3.3/1024)

Be careful, total no. of steps is 1024, not 1023.

The minimum external voltage reference you can use is 3.0V (if VDD ≧ 3.0V) or 1.8V (if VDD < 3.0V).

Hope this helps.
Tahmid.

 

[amilaachala]

are you sure??? i mean to find a step size

step size = (Vmax - Vmin) / 1024

that will give you the voltage difference between 2 steps Right?????????

 

[wp100]

Hi,

Tahmid is correct.

step size = ( vmax 3v3 - vmin 0v) / 1024 = 3v3 / 1024 = 0.003226 v per single step

Also see the chips datasheet, section electrical charactristics, for the operating voltages of the ADC of your particular type of chip F or LF

 

[amilaachala]

Hi,

Tahmid is correct.

step size = ( vmax 3v3 - vmin 0v) / 1024 = 3v3 / 1024 = 0.003226 v per single step

Also see the chips datasheet, section electrical charactristics, for the operating voltages of the ADC of your particular type of chip F or LF

If you look closely you will see that Tahmid has muliplied the equation you posted with an additional Vin.

 

[Tahmid]

The extra VIN was an error that I have fixed.