Table of Contents
Advertisement
Also, digital circuitry must be isolated from the analog input signals (AN0 to AN11), analog
reference power supply (V
Also, the analog ground (AV
on the board.
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 AN11) and analog
reference power supply (V
figure 16-7.
Also, the bypass capacitors connected to AV
to AN11 must be connected to AV
If a filter capacitor is connected as shown in figure 16-7, the input currents at the analog input pins
(AN0 to AN11) 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
), an error will arise in the analog input pin voltage. Careful consideration is therefore required
in
when deciding the circuit constants.
*1
*1
Notes:
Values are reference values.
*1
10 µF
*2 R
: Input impedance
in
Figure 16-7 Example of Analog Input Protection Circuit
), and analog power supply (AV
ref
) should be connected at one point to a stable digital ground (V
SS
) should be connected between AV
ref
CC
.
SS
100 Ω
in *2
R
0.1 µF
0.01 µF
) by the analog ground (AV
CC
and AV
CC
and V
and the filter capacitor connected to AN0
ref
AV
CC
V
ref
AN0 to AN11
AV
SS
).
SS
SS
as shown in
SS
)
605
Advertisement
Table of Contents
