m37905 Renesas Electronics Corporation., m37905 Datasheet - Page 537

• Manufacturer Part Number: m37905
• Description: Mitsubishi 16-bit Single-chip Microcomputer 7700 Family / 7900 Series
• Manufacturer: Renesas Electronics Corporation.

APPENDIX
Appendix 7. Countermeasure against noise
Fig. 6 Countermeasure example against noise for analog input pin using thermistor
20-106
3. Wiring for analog input pins, analog power source pins, etc.
(1) Processing for analog input pins
Notes 1: Design an external circuit for the ANi pin so that charge/discharge is available within 1
Thermistor
Reason: A signal which is input to the analog input pin is usually an output signal from a sensor.
Additionally, connect the resistor to the microcomputer as close as possible.
Connect a resistor to the analog signal line, which is connected to an analog input pin, in series.
Connect a capacitor between the analog input pin and the AVss pin, as close to the AVss pin as
possible.
2: This resistor and thermistor are used to divide resistance.
cycle of
The sensor, which detects changes in status, is installed far from the microcomputer’s
printed circuit board. Therefore, this long wiring between them becomes an antenna which
picks up noise and feeds it into the microcomputer’s analog input pin.
If a capacitor between an analog input pin and the AVss pin is grounded far away from the
AVss pin, noise on the GND line may enter the microcomputer through the capacitor.
Noise
AD
.
Not
acceptable
(Note 2)
7905 Group User’s Manual Rev.1.0
Acceptable
RI
CI
Acceptable
AVss
AN
M37905
i
Reference values
RI : Approximate 100
CI : Approximate 100 pF to 1000 pF
to 1000