MB90822 Ver la hoja de datos (PDF) - Fujitsu
Número de pieza
componentes Descripción
Fabricante
MB90822 Datasheet PDF : 100 Pages
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MB90820 Series
7. Notes on Using A/D Converter
• 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. Therefore, 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.
And if the sampling time cannot be sufficient, connect a capacitor of about 0.1 mF to the analog input pin.
• Analog input circuit model
Analog input
R
C
During sampling : ON
Comparator
Note : The values are reference values.
MB90822/823
MB90F822A/F823A
R
2.0 kΩ (Max)
2.0 kΩ (Max)
C
14.4 pF (Max)
16.0 pF (Max)
• The relationship between the external impedance and minimum sampling time
(External impedance = 0 kΩ to 100 kΩ)
100
90
MB90822/
80
823 MB90F822A/F823A
70
60
50
40
30
20
10
0
0
5 10 15 20 25 30 35
Minimum sampling time [µs]
(External impedance = 0 kΩ to 20 kΩ)
20
18
MB90822/
16
823 MB90F822A/F823A
14
12
10
8
6
4
2
0
0
1
2
3
4
5
6
7
8
Minimum sampling time [µs]
• About the error
The accuracy gets worse as | AVR−AVSS | becomes smaller.
94
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