7220 datasheet(227/303 Pages) RENESAS

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APPENDIX

6.3 Notes on use

7220 Group User’s Manual

6-8

6.3.6 Notes on A-D comparator

(1)

Signal source impedance for analog input

Make the signal source impedance for analog input low, or equip an analog input pin with an external

capacitor of 0.01

µF to 1 µF. Further, be sure to verify the operation of application products on the

user side.

Reason

An analog input pin includes the capacitor for analog voltage comparison. Accordingly, when signals

from signal source with high impedance are input to an analog input pin, charge and discharge noise

generates. This may cause the A-D comparison precision to be worse.

(2)

Note during an A-D conversion

The comparator consists of a capacity coupling, and a charge of the capacity will be lost if the clock

frequency is too low. Thus, make sure the following during an A-D comparison.

qf(XIN) is 500 kHz or more

qDo not execute the STP instruction and WIT instruction

6.3.7 Note on RESET pin

In case where the RESET signal rise time is long, connect a ceramic capacitor or others across the RESET

pin and the VSS pin. And use a 1000 pF or more capacitor for high frequency use. When connecting the

capacitor, note the following :

qMake the length of the wiring which is connected to a capacitor as short as possible.

qBe sure to check the operation of application products on the user side.

Reason

______

If the several nanosecond or several ten nanosecond impulse noise enters the RESET pin, it may cause

a microcomputer failure.

7220 Datasheet(PDF) 227 Page - Renesas Technology Corp