SH7125_08 Datasheet, PDF (521/774 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH™ RISC engine Family

Section 13 A/D Converter (ADC)
13.7.6 Notes on Noise Countermeasures
A protection circuit should be connected in order to prevent damage due to abnormal voltage, such
as an excessive surge at the analog input pins (AN0 to AN7), between AVcc and AVss, as shown
in figure 13.8. Also, the bypass capacitors connected to AVcc and the filter capacitor connected to
AN0 to AN7 must be connected to AVss.
If a filter capacitor is connected, the input currents at the analog input pins (AN0 to AN7) 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 circuit
constants.
R_in ^*2
100 Ω
*1
0.1 µF
Notes: Values are reference values.
1.
10 µF
0.01 µF
AV_cc
AN0 to AN7
AV_ss
2. Rin: Input impedance
Figure 13.8 Example of Analog Input Protection Circuit
Table 13.7 Analog Pin Specifications
Item
Analog input capacitance
Permissible signal source impedance
Min.



Max. Unit
20
pF
3
kΩ
1
kΩ
Condition

Conversion time ≥ 4.0 µs
Conversion time < 4.0 µs
Rev. 4.00 Jul. 25, 2008 Page 501 of 750
REJ09B0243-0400