Datasheet

Section 24 A/D Converter
REJ09B0465-0300 Rev. 3.00 Page 847 of 982
Sep 17, 2010
H8S/20103, H8S/20203, H8S/20223, H8S/20115, H8S/20215, H8S/20235 Group
24.8.6 Notes on Noise Countermeasures
A protection circuit connected to prevent damage due to an abnormal voltage such as an excessive
surge at the analog input pins (AN0 to AN11, AN0_2 to AN3_2) should be connected between
AVcc and AVss as shown in figure 24.12. Also, the bypass capacitors connected to AVcc and the
filter capacitor connected to AN0 to AN11 or AN0_2 to AN3_2 must be connected to AVss.
If a filter capacitor is connected, the input currents at the analog input pins (AN0 to AN1, AN0_2
to AN3_2) are averaged, and so an error may arise. Also, when A/D conversion is performed
frequently, as in scan mode, if the current charged and discharged by the capacitance of the
sample-and-hold circuit in the A/D converter exceeds the current input via the input impedance
(R
in
), an error will arise in the analog input pin voltage. Careful consideration is therefore required
when deciding the circuit constants.
AV CC
* 1
AN0 to AN11, AN0_2 to AN3_2
AV
SS
Notes:
1.
2. R
in
: Input impedance
R
in
* 2
100 Ω
0.1 µF
0.01 µF10 µF
Values are reference values.
Figure 24.12 Example of Analog Input Protection Circuit