mb95r203a Fujitsu Microelectronics, Inc., mb95r203a Datasheet - Page 40

• Manufacturer Part Number: mb95r203a
• Description: 8-bit Proprietary Microcontrollers
• Manufacturer: Fujitsu Microelectronics, Inc.

MB95R203A
40
• About the external impedance of analog input and its sampling time
• About errors
(2) Notes on Using A/D Converter
• 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
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.
|V
Note : The values are reference values.
CC
− V
[External impedance = 0 kΩ to 100 kΩ]
SS
100
90
80
70
60
50
40
30
20
10
| becomes smaller, values of relative errors grow larger.
0
0
Minimum sampling time [μs]
5
Analog input
10
15
20
25
30
2.7 V ≤ Vcc ≤ 3.6 V : R : = 5.3 kΩ (Max) , C : = 8.5 pF (Max)
35
40
R
During sampling : ON
C
[External impedance = 0 kΩ to 20 kΩ]
20
18
16
14
12
10
8
6
4
2
0
0
Minimum sampling time [μs]
Comparator
1
2
3
DS07-12630-1E
4