MB89480 Datasheet, PDF (42/55 Pages) Fujitsu Component Limited. – 8-bit Proprietary Microcontroller

MB89480/480L Series
(3) Notes on Using A/D Converter
• Input impedance of the analog input pins
The A/D converter used for the MB89480 series contains a sample and hold circuit as illustrated below to
fetch analog input voltage into the sample and hold capacitor for 16 instruction cycles after activation A/D
conversion.
For this reason, if the output impedance of the external circuit for the analog input is high, analog input
voltage might not stabilize within the analog input sampling period. Therefore, it is recommended to keep
the output impedance of the external circuit low.
Note that if the impedance cannot be kept low, it is recommended to connect an external capacitor of about
0.1 µF for the analog input pin.
Analog Input Circuit Model
Sample hold circuit
If the analog input
impedance is higher
than 10 kΩ, it is
recommended to
connect an external
capacitor of approx.
0.1 µF.
Analog input pin
Comparator
R
C
Close for 16 instruction cycles after
activating A/D conversion.
Analog channel selector
R: analog input equivalent resistance
C: analog input equivalent capacitance
MB89485
MB89PV480
2.2 kΩ
45 pF
MB89485L
2.8 kΩ
46 pF
MB89P485
2.6 kΩ
28 pF
MB89P485L
7.1 kΩ
48.3 pF
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