MB2146-301A Fujitsu Microelectronics, Inc., MB2146-301A Datasheet - Page 55

• Manufacturer Part Number: MB2146-301A
• Description: 8-bit Microcontrollers
• Manufacturer: Fujitsu Microelectronics, Inc.

(2) Notes on Using A/D Converter
• External impedance of analog input and its sampling time
• Errors
• Analog input equivalent circuit
• The relationship between external impedance and minimum sampling time
• A/D converter with sample and hold circuit. If the external impedance is too high to keep sufficient sampling
As |AV
Note : The values are reference values.
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.
Analog input
(External impedance = at 0 kΩ to 100 kΩ)
CC
100
− AV
90
80
70
60
50
40
30
20
10
0
0
SS
Minimum sampling time [µs]
| becomes smaller, values of relative errors grow larger.
2
During sampling : ON
AV
4
CC
≥ 4.5 V
6
8
AV
10
CC
≥ 4.0 V
12
R
4.5 V ≤ AV
4.0 V ≤ AV
14
C
CC
CC
≤ 5.5 V
< 4.5 V
(External impedance = at 0 kΩ to 20 kΩ)
Comparator
20
18
16
14
12
10
8
6
4
2
0
MB95130MB Series
0
Minimum sampling time [µs]
2.0 kΩ (Max)
8.2 kΩ (Max)
AV
CC
≥ 4.5 V
1
R
2
16 pF (Max)
16 pF (Max)
AV
CC
3
C
≥ 4.0 V
4
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