ST STM8S Application Note page 11

AN2752
Equation 1:
C = C
VIN
where:
●
C
VIN
●
C
SAMP
●
C
EXT
parasitic routing capacitance, pad and pin capacitance and external capacitance. To
ensure proper and accurate sampling the following equation must be satisfied
Equation 2:
(
R R
+
SW
where:
●
R
SW
●
R
EXT
●
C
SAMP
●
T = 0.5 µs (for 2 MHz input CLK)
S
Equation 2
ADC.
Please refer to the Root part number 2 datasheet and/or the corresponding family reference
manual (RM0016) for more details.
+ C
SAMP EXT
is the total equivalent capacitor on the path of V
is the equivalent sampling capacitance
is the total external capacitance on the path of V
) × ( )
C C
+
EXT SAMP EXT
= 30 kOhm
is the total external resistance on the path of V
= 3 pF
is specific for R and C
EXT
Doc ID 14651 Rev 3
⎛ 3 ⎞
< ×
----- -
T
⎝ ⎠
S
10
when designing an analog input interface for the
EXT
Analog-to-digital converter (ADC)
IN
to the macro pin. This includes
IN
IN
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