mb90f378 Fujitsu Microelectronics, Inc., mb90f378 Datasheet - Page 59

• Manufacturer Part Number: mb90f378
• Description: 16-bit Proprietary Microcontroller
• Manufacturer: Fujitsu Microelectronics, Inc.

7. Notes on Using A/D Converter
• About the external impedance of the analog input and its sampling time
• About errors
Note : The values are reference values.
• A/D converter with sample and hold circuit. If the external impedance is too high to keep sufficient sampling
• To satisfy the A/D conversion precision standard, consider the relationship between the external impedance
• If the sampling time cannot be sufficient, connect a capacitor of about 0.1 µF to the analog input pin.
As |AVR − AV
• The relationship between the external impedance and minimum sampling time
• Analog input circuit model
time, the analog voltage charged to the internal sampling and hold capacitor is insufficient, adversely affecting
A/D conversion precision.
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.
[External impedance = 0 kΩ to 100 kΩ]
100
90
80
70
60
50
40
30
20
10
0
0
SS
| becomes smaller, values of relative errors grow larger.
5
Minimum sampling time (µs)
Analog input
10
15
20
MB90F378/V378
During sampling : ON
25
30
↑
35
R
20
18
16
14
12
10
8
6
4
2
0
[External impedance = 0 kΩ to 20 kΩ]
0
C
MB90F378/V378
1
Minimum sampling time (µs)
2
Comparator
3
MB90378 Series
4
1.9 kΩ (Max)
MB90F378/V378
5
R
6
7
25 pF (Max)
8
C
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