SH7080 Datasheet, PDF (1032/1644 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer SuperH™ RISC engine Family

Section 19 A/D Converter (ADC)
19.7.6 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 AN15), between AVcc and AVss, as shown
in figure 19.8. Also, the bypass capacitors connected to AVcc and the filter capacitor connected to
AN0 to AN15 must be connected to AVss.
If a filter capacitor is connected, the input currents at the analog input 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_in), an error will arise in
the analog input pin voltage. Careful consideration is therefore required when deciding circuit
constants.
*1 *1
R_in ^*2
100 Ω
0.1 µF
Notes: Values are reference values.
1.
10 µF
0.01 µF
AV_cc
AV_ref
AN0 to AN15
AV_ss
2. Rin: Input impedance
Figure 19.8 Example of Analog Input Protection Circuit
Table 19.7 Analog Pin Specifications
Item
Analog input capacitance
Permissible signal source impedance
Min.


Max.
Unit
20
pF
3
kΩ
1
Condition

Pφ ≤ 20 MHz
Pφ > 20 MHz
Rev. 3.00 May 17, 2007 Page 974 of 1582
REJ09B0181-0300