MB89935B データシートの表示（PDF） - Fujitsu

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MB89935B

8-bit Proprietary Microcontroller

Fujitsu 

MB89930A Series

(3) Notes on Using A/D Converter

• Input impedance of the analog input pins

The A/D converter used for the MB89930A series contains a sample hold circuit as illustrated below to fetch

analog input voltage into the sample hold capacitor for 16 instruction cycles after activating 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 (below 4 kΩ) .

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 Equivalent Circuit

Analog input pin

Sample hold circuit

RC

Comparator

If the analog input

impedance is higher than

4 kΩ, it is recommended to

connect an external

capacitor of approx. 0.1 µF.

Close for 16 instruction cycles after

activating A/D conversion

Analog channel selector

MB89935A/B R = approx. 2.2 kΩ, C = approx. 45 pF

MB89P935B R = approx. 3.2 kΩ, C = approx. 30 pF

• Error

The smaller the | VCC − AVSS |, the greater the error would become relatively.

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