4571 datasheet(60/126 Pages) RENESAS

60 / 126 page

Rev.1.02

May 25, 2007

Page 60 of 124

REJ03B0179-0102

4571 Group

2. Connection of bypass capacitor across VSS line

and VDD line

Connect an approximately 0.1

µF bypass capacitor across the

VSS line and the VDD line as follows:

• Connect a bypass capacitor across the VSS pin and the VDD pin

at equal length.

• Connect a bypass capacitor across the VSS pin and the VDD pin

with the shortest possible wiring.

• Use lines with a larger diameter than other signal lines for VSS

line and VDD line.

• Connect the power source wiring via a bypass capacitor to the

VSS pin and the VDD pin.

Fig 65. Bypass capacitor across the VSS line and the

VDD line

3. Wiring to analog input pins

• Connect an approximately 100

Ω to 1 kΩ resistor to an analog

signal line which is connected to an analog input pin in series.

Besides, connect the resistor to the microcomputer as close as

possible.

• 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 the analog input pin and the Vss pin at equal length.

Signals which is input in an analog input pin (such as an A/D

converter/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 functions as an antenna which feeds noise into the

microcomputer, which causes noise to an analog input pin.

Fig 66. Analog signal line and a resistor and a capacitor

VSS

VDD

VSS

VDD

N.G.

O.K.

Thermistor

Analog

input pin

(Note)

N.G.

O.K.

VSS

Note : The resistor is used for dividing

resistance with a thermistor.

Microcomputer

Noise

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