3886 datasheet(237/380 Pages) RENESAS

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3886 Group User’s Manual

APPLICATION

2.7 A-D converter

2.7.4 Notes on A-D converter

(1)

Analog input pin

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.

q 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 conversion precision to be worse.

(2)

A-D converter power source pin

The AVSS pin is an A-D converter power source pin. Regardless of using the A-D conversion function

or not, connect them as following :

• AVSS : Connect to the VSS line

q Reason

If the AVSS pin id opened, the microcomputer may have a failure because of noise or others.

(3)

Clock frequency during 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 conversion.

• f(XIN) is 500 kHz or more

• Do not execute the STP instruction

3886 Datasheet(PDF) 237 Page - Renesas Technology Corp