Atmel SAM4L Xplained Pro Evaluation Kit Atmel ATSAM4L-XPRO ATSAM4L-XPRO Data Sheet

42023ES–SAM–07/2013

The analog voltage source must be able to charge the sample and hold (S/H) capacitor in the
ADC in order to achieve maximum accuracy. Seen externally the ADC input consists of a resis-
tor (

) and a capacitor (

). In addition, the source resistance (

) must be

taken into account when calculating the required sample and hold time. 

 shows the

ADC input channel equivalent circuit.

ADC Input

To achieve n bits of accuracy, the 

 capacitor must be charged at least to a voltage of 

The minimum sampling time 

 for a given 

can be found using this formula:

for a 12 bits accuracy : 

where

PSRR

(1)

fvdd=1Hz, ext ADVREFP=3.0V 
VDDIO=3.6V

100

dB

fvdd=2MHz, ext 
ADVREFP=3.0V VDDIO=3.6V

50

DC supply current

(1)

VDDANA=3.6V, 
ADVREFP=3.0V

1

1.8

mA

VDDANA=1.6V, 
ADVREFP=1.0V

1

1.3

1.

These values are based on simulation. These values are not covered by test limits in production or characterization.

2.

These values are based on characterization and not tested in production, and valid for an input voltage between 10% to 90% of 
reference voltage.

Unipolar mode, gain=1

R

SOURCE

R

SAMPLE

Analog Input 

ADx

C

SAMPLE

V

IN

VDDANA/2

≥

1

2

1

+

(

)

–

–

(

)

×

+

(

)

(

)

×

1

+

(

)

2

( )

ln

×

×

≥

+

(

)

(

)

×

9

×

02

,

≥

1

2

×

------------------------

=