mb95f118awpv2 Fujitsu Microelectronics, Inc., mb95f118awpv2 Datasheet - Page 56

• Manufacturer Part Number: mb95f118awpv2
• Description: 8-bit Proprietary Microcontrollers
• Manufacturer: Fujitsu Microelectronics, Inc.

56
MB95110A Series
(2) Notes on Using A/D Converter
• About the external impedance of analog input and its sampling time
• About errors
• The relationship between external impedance and minimum sampling time
• Analog input equivalent circuit
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. Also,
if the sampling time cannot be sufficient, connect a capacitor of about 0.1 µF to the analog input pin.
As |AV
Note : The values are reference values.
Analog input pin
(External impedance = 0 kΩ to 100 kΩ)
CC
100
90
80
70
60
50
40
30
20
10
0
− AV
0
Minimum sampling time [µs]
SS
5
| becomes smaller, values of relative errors grow larger.
AVcc ≥ 2.7 V
10
15
During sampling
20
AVcc ≥ 1.8 V
25
30
:
35
ON
40
2.7 V ≤ AVcc ≤ 3.6 V
1.8 V ≤ AVcc < 2.7 V
R
C
(External impedance = 0 kΩ to 20 kΩ)
20
18
16
14
12
10
8
6
4
2
0
0
Comparator
Minimum sampling time [µs]
1.7 kΩ (Max)
84 kΩ (Max)
1
R
2
AVcc ≥ 2.7 V
14.5 pF (Max)
25.2 pF (Max)
3
C
4