MB91350A データシートの表示（PDF） - Fujitsu

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MB91350A

32-Bit Proprietary Microcontroller

Fujitsu 

MB91350A Series

• About the external impedance of the 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.

• Analog input circuit model

R

Analog input

C

During Sampling : ON

Comparator

Note : The values are reference values.

MB91355A

MB91F355A

MB91F356B

R

0.18 kΩ (Max)

0.18 kΩ (Max)

0.18 kΩ (Max)

C

63.0 pF (Max)

39.0 pF (Max)

39.0 pF (Max)

• To satisfy the A/D conversion precision standard, consider the relationship between the external impedance

and minimum sampling time and either adjust the resistor value and operating frequency or decrease the

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

• The relationship between the external impedance and minimum sampling time

(External impedance = 0 kΩ to 100 kΩ)

100

90

80

70

60

50

40

30

20

10

0

0

MB91F355A/MB91F356B

MB91355A

5 10 15 20 25 30 35

Minimum sampling time [µs]

(External impedance = 0 kΩ to 20 kΩ)

MB91F355A/MB91F356B

20

18

16

14

12

MB91355A

10

8

6

4

2

0

012345678

Minimum sampling time [µs]

• If the sampling time cannot be sufficient, connect a capacitor of about 0.1 µF to the analog input pin.

• About errors

As |AVRH-AVSS| becomes smaller, values of relative errors grow larger.

101

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