ST STM8S

AN2752 Rev 6 11/40
AN2752 Analog-to-digital converter (ADC)
39
Equation 1:
where:
• C
VIN
is the total equivalent capacitor on the path of V
IN
• C
SAMP
is the equivalent sampling capacitance
• C
EXT
is the total external capacitance on the path of V
IN
to the macro pin. This includes
parasitic routing capacitance, pad and pin capacitance and external capacitance. To
ensure proper and accurate sampling the following equation must be satisfied
Equation 2:
where:
• R
SW
= 30 kΩ
• R
EXT
is the total external resistance on the path of V
IN
• C
SAMP
= 3 pF
• T
S
= 0.5 µs (for 2 MHz input CLK)
Equation 2 is specific for R
EXT
and C
EXT
when designing an analog input interface for the
ADC.
Refer to the STM8S or STM8AF datasheets and/or to reference manual RM0016 (available
on www.st.com) for more details.
C
VIN
C
SAMP
C
EXT
+=
R
SW
R
EXT
+()C
SAMP
C
EXT
+()×
3
10
------
⎝⎠
⎛⎞
T
S
×<