参数资料
型号: MB90F803SPF-G
厂商: FUJITSU LTD
元件分类: 微控制器/微处理器
英文描述: 16-BIT, FLASH, 25 MHz, MICROCONTROLLER, PQFP100
封装: 20 X 14 MM, 3.35 MM HEIGHT, 0.65 MM PITCH, PLASTIC, QFP-100
文件页数: 81/92页
文件大小: 2178K
代理商: MB90F803SPF-G
MB90800 Series
82
DS07-13733-6E
(2) Notes on Using A/D Converter
About the external impedance of analog input and its sampling time
A/D converter with sample & 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 relation-ship
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
μF to the analog input pin.
About errors
As | AVCC
AVSS | becomes smaller, values of relative errors grow larger.
Analog input circuit model
R
C
Comparator
Analog input
RC
MB90803 (S)
1.9 k
Ω (Max) 32.3 pF (Max)
MB90F804-201(101)/F803(S)/F809(S)
1.9 k
Ω (Max) 25.0 pF (Max)
MB90V800
1.9 k
Ω (Max) 32.3 pF (Max)
Note : The values are reference values.
During sampling : ON
100
90
80
70
60
50
40
30
20
10
0
5
10
15
20
25
30
35
MB90803(S)/
MB90V800
MB90F804-201(101)/
MB90F803(S)/
MB90F809(S)
20
18
16
14
12
10
8
6
4
2
0
012
3
45
7
MB90803(S)/
MB90V800
8
MB90F804-201(101)/
MB90F803(S)/
MB90F809(S)
6
(External impedance
= 0 kΩ to 100 kΩ)
(External impedance
= 0 kΩ to 20 kΩ)
Minimum sampling time [
μs]
Minimum sampling time [
μs]
External
impedance
[k
Ω
]
External
impedance
[k
Ω
]
The relationship between external impedance and minimum sampling time
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