
MB90330 Series
109
Notes :
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 presicion.
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.
If the sampling time cannot be sufficient, connect a capacitor of about 0.1
μ
F to the analog input pin.
About errors
As
|
AVRH
|
becomes smaller, values of relative errors grow larger.
R
C
Analog input
Comparator
Analog input circuit model
During sampling : ON
Note : The values are reference values.
MB90333A
MB90F334A
MB90V330A
R
1.9 k
(Max)
1.9 k
(Max)
1.9 k
(Max)
C
32.3 pF (Max)
25.0 pF (Max)
32.3 pF (Max)
100
90
80
70
60
50
40
30
20
10
0
0
5
10
15
20
25
30
35
MB90333A/
MB90V330A
MB90F334A
20
18
16
14
12
10
8
6
4
2
0
0
1
2
3
4
5
6
8
7
MB90F333A/
MB90V330A
MB90F334A
(External impedance
=
0 k
to 100 k
)
E
]
Minimum sampling time [
μ
s]
(External impedance
=
0 k
to 20 k
)
E
]
Minimum sampling time [
μ
s]
The relationship between the external impedance and minimum sampling time