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7542 Group
2. Connection of bypass capacitor across V
Connect an approximately 0.1 µ F bypass capacitor across the V
line and the V
line as follows:
CC
• Connect a bypass capacitor across the V
at equal length.
• Connect a bypass capacitor across the V
with the shortest possible wiring.
• Use lines with a larger diameter than other signal lines for V
line and V
line.
CC
• Connect the power source wiring via a bypass capacitor to the
V
pin and the V
pin.
SS
CC
V
CC
V
SS
N.G.
Fig. 88 Bypass capacitor across the V
Rev.3.02
Oct 31, 2006
REJ03B0006-0302
line and V
line
SS
CC
pin and the V
SS
CC
pin and the V
SS
CC
V
CC
V
SS
O.K.
line and the V
SS
CC
Page 69 of 134
3. Wiring to analog input pins
• Connect an approximately 100 Ω to 1 kΩ resistor to an analog
SS
signal line which is connected to an analog input pin in series.
pin
Besides, connect the resistor to the microcomputer as close as
possible.
pin
• Connect an approximately 1000 pF capacitor across the Vss pin
and the analog input pin. Besides, connect the capacitor to the
Vss pin as close as possible. Also, connect the capacitor across
SS
the analog input pin and the Vss pin at equal length.
<Reason>
Signals which is input in an analog input pin (such as an A/D con-
verter/comparator input pin) are usually output signals from
sensor. The sensor which detects a change of event is installed far
from the printed circuit board with a microcomputer, the wiring to
an analog input pin is longer necessarily. This long wiring func-
tions as an antenna which feeds noise into the microcomputer,
which causes noise to an analog input pin.
Noise
line
Thermistor
Fig. 89 Analog signal line and a resistor and a capacitor
• The analog input pin is connected to the capacitor of a voltage
comparator. Accordingly, sufficient accuracy may not be ob-
tained by the charge/discharge current at the time of A/D
conversion when the analog signal source of high-impedance is
connected to an analog input pin. In order to obtain the A/D con-
version result stabilized more, please lower the impedance of an
analog signal source, or add the smoothing capacitor to an ana-
log input pin.
(Note)
Microcomputer
N.G.
O.K.
V
Note : The resistor is used for dividing
resistance with a thermistor.
Analog
input pin
SS
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