7480 datasheet(255/337 Pages) RENESAS

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7480 Group and 7481 Group User's Manual

2-40

2.8 Countermeasures against Noise

APPLICATIONS

2.8.2 Connection of Bypass Capacitor across VSS

Line and VCC Line

Connect an approximately 0.1

µF bypass capacitor

across the VSS line and the VCC line as follows:

• Connect a bypass capacitor across the VSS pin

and the VCC pin at equal length.

• Connect a bypass capacitor across the VSS pin

and the VCC pin with the shortest possible wiring.

• Use lines with a larger diameter than other signal

lines for VSS line and VCC line.

• Connect the power source line to VSS pin and

VCC pin through a bypass capacitor.

2.8.3 Connection of Bypass Capacitor across VSS

Line and VREF Line

Connect an approximately 0.01

µF bypass capacitor

across the VSS line and the VREF line as follows:

• Connect a bypass capacitor across the VSS pin

and the VREF pin at equal length.

• Connect a bypass capacitor across the VSS pin

and the VREF pin with the shortest possible wiring.

• Use lines with a larger diameter than other signal

lines for VSS line and VREF line.

2.8.4 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 0.1 to 1

µF 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.

REASON

Signals which is input in an analog input pin (such

as an A-D converter 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.

If a capacitor between an analog input pin and the

VSS pin is grounded at a position far away from the

VSS pin, noise on the GND line may enter a

microcomputer through the capacitor.

Figure 2.8.4 Bypass Capacitor across VSS Line and

VCC Line

Figure 2.8.5 Bypass Capacitor across VSS Line and

VREF Line

Figure 2.8.6 Analog Signal Line and Resistor and

Capacitor

N.G.

O.K.

VSS

Analog

input pin

Microcomputer

(Note)

Thermistor

Noise

Note:The resistor is used for dividing

resistance with a thermistor.

VSS

VCC

VSS

VCC

N.G.

O.K.

VSS

VREF

VSS

VREF

N.G.

O.K.

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