MB95F133JS datasheet(54/63 Pages) FUJITSU

54 / 63 page

MB95130M Series

(2) Notes on Using A/D Converter

• External impedance of analog input and its sampling time

• A/D converter with sample and hold circuit. If the external impedance is too high to keep sufficient sampling

time, the analog voltage charged to the internal sample and hold capacitor is insufficient, adversely affecting

A/D conversion precision. Therefore to satisfy the A/D conversion precision standard, consider the relationship

between the external impedance and minimum sampling time and either adjust the register value and operating

frequency or decrease the external impedance so that the sampling time is longer than the minimum value.

Also, if the sampling time cannot be sufficient, connect a capacitor of about 0.1

µF to the analog input pin.

• Errors

As |AVCC

− AVSS| becomes smaller, values of relative errors grow larger.

Analog input

Note : The values are reference values.

• Analog input equivalent circuit

4.5 V

≤ AVCC ≤ 5.5 V

2.0 k

Ω (Max)

16 pF (Max)

4.0 V

≤ AVCC < 4.5 V

8.2 k

Ω (Max)

16 pF (Max)

Comparator

During sampling : ON

100

(External impedance

= at 0 kΩ to 100 kΩ)

(External impedance

= at 0 kΩ to 20 kΩ)

Minimum sampling time [

µs]

Minimum sampling time [

µs]

AVCC

≥ 4.0 V

• The relationship between external impedance and minimum sampling time

AVCC

≥ 4.5 V

AVCC

≥ 4.5 V

AVCC

≥ 4.0 V

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