Atmel SAM4S Series, Предварительный информационный лист

Страница: 1117 / 1163

1117
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
During the tracking phase the ADC needs to track the input signal during the tracking time
shown below:
• 10-bit mode: t
TRACK
= 0.042 x Z 160
• 12-bit mode: t
TRACK
= 0.054 x Z 205
With t
TRACK
expressed in ns and Z
SOURCE
expressed in Ohms.
Two cases must be considered:
1. The calculated tracking time (t
TRACK
) is lower than 15 t
CP_ADC
.
Set TRANSFER = 1 and TRACTIM = 0.
In this case, the allowed Zsource can be computed versus the ADC frequency with the hypothe-
sis of t
TRACK
= 15 × t
CP_ADC
:
Where t
CP_ADC
= 1/f
ADC
.
2. The calculated tracking time (t
TRACK
) is higher than 15 t
CP_ADC
.
Set TRANSFER = 1 and TRACTIM = 0.
In this case, a timer will trigger the ADC in order to set the correct sampling rate according to the
Track time.
The maximum possible sampling frequency will be defined by t
TRACK
in nano seconds, computed
by the previous formula but with minus 15 × t
CP_ADC
and plus TRANSFER time.
• 10 bit mode: 1/f
S
= t
TRACK
- 15 × t
CP_ADC
+ 5 t
CP_ADC
• 12 bit mode: 1/f
S
= t
TRACK
- 15 × t
CP_ADC
+ 5 t
CP_ADC
Note: Csample and Ron are taken into account in the formulas
f
ADC
= ADC clock (MHz) Z
SOURCE
(kOhms) for 12 bits Z
SOURCE
(kOhms) for 10 bits
20.00 10 14
16.00 14 19
10.67 22 30
8.00 31 41
6.40 40 52
5.33 48 63
4.57 57 74
4.00 66 85
3.56 74 97
3.20 83 108
2.91 92 119
2.67 100 130
2.46 109 141
2.29 118 152
2.13 126 164
2.00 135 175
1.00 274 353