Notes On Noise Countermeasures; Figure 15.10 Example Of Analog Input Protection Circuit; Table 15.6 Analog Pin Specifications - Renesas H8SX/1500 Series Hardware Manual

15.7.6

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 AN15) should be connected between AVcc0, AVcc1 and
AVss as shown in figure 15.10. Also, the bypass capacitors connected to AVcc0 and AVcc1 and
the filter capacitor connected to pins AN0 to AN15 must be connected to AVss.
If a filter capacitor is connected, the input currents at pins AN0 to AN15 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
input pin voltage. Careful consideration is therefore required when deciding the circuit constants.
1
*
Notes: Values are reference values.
1.
2. R

Figure 15.10 Example of Analog Input Protection Circuit

Table 15.6 Analog Pin Specifications

Item
Analog input capacitance
Permissible signal source impedance
100 Ω
2
R *
in
0.1 µF
10 µF 0.01 µF
: Input impedance
in
), an error will arise in the analog
in
AV and AV
CC0 CC1
AN0 to AN15
AV
SS
Min Max

20

5
Rev. 3.00 Mar. 14, 2006 Page 565 of 804
Section 15 A/D Converter
Unit
pF
kΩ
REJ09B0104-0300