Datasheet

Section 17 A/D Converter
Rev.7.00 Mar. 18, 2009 page 820 of 1136
REJ09B0109-0700
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 the circuit
constants.
AV CC
*
1
*
1
Vref
AN0 to AN15
AV SS
Notes: Values are reference values.
1.
2. R
in
: Input impedance
R
in
*
2
100Ω
0.1 µF
0.01 µF10 µF
Figure 17.7 Example of Analog Input Protection Circuit
Table 17.6 Analog Pin Specifications
Item Min Max Unit
Analog input capacitance — 20 pF
Permissible signal source impedance — 10 kΩ