Notes On Noise Countermeasures; Figure 15.10 Example Of Analog Input Protection Circuit; Table 15.6 Analog Pin Specifications - Renesas H8SX/1520 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.
Notes:

Table 15.6 Analog Pin Specifications

Item
Analog input capacitance
Permissible signal source impedance
Downloaded from Elcodis.com electronic components distributor
2
R *
in
1
*
Values are reference values.
1.
10 µF 0.01 µF
2. R : Input impedance
in

Figure 15.10 Example of Analog Input Protection Circuit

AV and AV
CC0
100 Ω
AN0 to AN15
0.1 µF
AV
SS
Min


Rev. 3.00 Mar. 14, 2006 Page 565 of 804
Section 15 A/D Converter
), an error will arise in the analog
in
CC1
Max Unit
20 pF
5 kΩ
REJ09B0104-0300