Datasheet

Section 20 A/D Converter
Rev. 4.00 Sep 27, 2006 page 631 of 1130
REJ09B0327-0400
Also, the bypass capacitors connected to AVCC, AVref and the filter capacitor connected to AN0
to AN7 must be connected to AVSS.
If a filter capacitor is connected as shown in figure 20.7, 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 the circuit constants.
AVCC
*
1
AVref
AN0 to AN7
AVSS
Notes: Figures are reference values.
1.
2. R
in
: Input impedance
*
1
R
in
*
2
100 Ω
0.1 µF
0.01 µF10 µF
Figure 20.7 Example of Analog Input Protection Circuit
Table 20.5 Analog Pin Ratings
Item Min Max Unit
Analog input capacitance — 20 pF
Permissible signal source impedance — 10
*
kΩ
Note: * When V
CC
= 4.0 to 5.5 V and φ ≤ 12 MHz.